- Parts List
- Getting Started
- Install Piston Rings
- Install Piston in Cylinder
- Oiling Cams, Followers, Connecting Rod, Piston Skirt
- Apply Gasket Cement
- Install Push Rod Tube Rubber Gaskets
- Installing Cylinder and Wrist Pin
- Install the Head Gasket, Head and Rocker Arm Assembly
- Installing the Other Side
OTtrical work I did in these write-ups.
- 11 BMW R75/5 Refinish Cylinders and Refinish & Rebuild Heads
- 11 BMW R75/5 Measure Cylinders and Install Pistons & New Rings
- 11 BMW R75/5 Install the Engine In the Frame
- 61 BMW R75/5 Install Electrical System
My resources are primarily from Oak Okleshen and Bob Fleischer. Oak publishes “Manual 1: Boxer Top End Disassembly, 1970-1975” and “Manual 2: Boxer Top End Reassembly 1970-1975” in a single bound booklet.
Oak died in April 2017. Consequently I don’t know if this manual will continue to be available any longer or by what means.
Bob has content on top end assembly and other details at his web site:
- Disassembly & Assembly of heads, pistons & rings to cylinders
- Pistons, rings, etc.
- Chemicals, Oils, etc.
- Setting Valves, Alignment of the rockers, End clearance
I also read through Anton Largiader’s material on rocker arms.
Here are the new parts I used.
|11 12 1 338 426||Valve cover gasket||2|
|11 12 1 338 716||Head gasket||2|
|11 11 1 255 001||Base gasket, Normal||2|
|07 11 9 934 460||C-clip, Wrist spin||4|
|11 32 1 250 267||Push Rod Tube, seal||4|
Here are the special tools and base gasket cement I used.
NOTE: I chose to use Hylomar gasket cement. Bob and Oak no longer recommend it. They have various “recommendations” for cement, and recommendations have changed over time with Hylomar being recommended at one time. See Oak and Bob’s material for more details. I bought Hylomar for my Silver Ghost build so I’ll get to see how well it holds up on both bikes.
The other tools are a ring expander (left side) and ring compressor (right side). Neither are required. In the previous top end work I’ve done, I used my fingers to install the rings into the grooves in the pistons and the pistons into the cylinders. But for this project, I added some new tools to the tool box.
I also tried some Permatex Engine Assembly Lube on the cam, cam followers, push rod ends and wrist pins. In the past, I had just oiled them.
This is how the bike looks when I start.
Find The Cylinder on Compression Stroke
Following Oak’s method, I determined which side is on compression when the engine is at top dead center and that’s the side I will assemble. Looking at the cam shaft I can see which side has the cam followers on the heel of the cam. The heal is the end of the cam lobe that is circular without the bump, or nose, which is on the other side of the cam lobe.
The shiny metal surfaces on the horizontal cam shaft are the cam lobes. The cylinders at 90 degrees to the cam shaft are cast sleeves the cam followers fit inside of: exhaust (left side) and intake (right side). The blurry bar in the middle is the connecting rod.
NOTE: The cam follower is NOT centered on the cam lobe and that is the CORRECT orientation of the cam follower on the cam lobe. The cam shaft is installed correctly and is NOT out of alignment.
BMW locates the cam shaft so the cam follower rides on one side of the cam lobe. The friction between the rotating cam lobe and the cam follower riding on top of the lobe creates a torque on the cam follower causing it to spin. In turn, the spinning cam follower spins the push rod riding on top. This evens the wear on the cam follower and the ball ends of the push rod.
In the picture below, you can clearly see the end of the cam follower sticking our of the cast sleeve riding on the cam lobe is offset from the center line of the cam lobe.
Install Piston Rings
Earlier, I ground the ends of the rings to set the end gap and stored the rings in the cylinders for safe keeping. Here is the bottom, or oil control ring, which is the first to go on the piston.
I install the rings starting with the bottom ring ending with the top ring. Note that each ring is different as it is designed for a different job. Each is marked with “Top” to show the side of the ring that faces up.
In the past, I used my fingers to spread the ring ends to get them to slide down the piston into the correct groove. But, I have a new ring expander tool and I use it this time. Here is how the ring fits in the jaws of the expander.
WARNING: Rings are very hard and that means they are brittle. They don’t like being bent. As I was “playing” with the expander and the oil control ring, I found out it is very easy to expand the ring too far and snap it in two :-(.
When you put a ring on the piston, expand it just enough to slip down the piston and into the groove. Don’t give a mighty squeeze on the ring expander or you, like I, get to buy another set of rings. Lesson learned, and reinforced, with a current retail price of $65.00 for a ring set and a week and a half to wait for a new ring set.
Here is the piston with all three rings installed. I confirm that “Top” is visible on all three.
NOTE: The picture below is NOT the correct orientation of the rings and the ring gaps. Keep reading to see how they are oriented on the left and right pistons.
I rotate the rings so the gaps are about 120 degrees apart. In the picture below of the left piston, you can see the orientation of the top ring (4:30) and middle ring (10:30) while the bottom ring (not visible) is at 1:30.
Oak uses different orientations for the left side and right side to help get them placed correctly to keep the gaps away from the thrust side (top and bottom) of the piston. By the way, I have read that rings “flutter” and rotate in their grooves so orienting them so the gaps are 120 degrees apart doesn’t mean they stay that way. Nonetheless, they are oriented to avoid the gaps lining up so they should seal well when the engine first starts up.
Install Piston in Cylinder
Now that the rings are installed in the piston, I install the piston in the cylinder. I wash the cylinder in hot soapy water and the rinse and dry it. I use a couple drops of engine oil to wet my fingers and wipe the cylinder walls so they have a very light coating of oil. A light coat will provide some lubrication at first start and ensure the rings seat into the new cross-hatching in the cylinder wall for a good seal to minimize oil consumption.
Correct Piston Orientation
I’m working with the left cylinder and piston and I want to ensure the piston is facing in the correct direction in the cylinder. The top of the piston has an arrow and “VORN” stamped into it. The arrow points to the front of the bike, and Vorn is German which loosely translates to “This Way Stupid!!”, or more formally, “Forward” :-).
I use the ring compressor tool to compress the rings into the grooves so I can gently push the piston and rings into the cylinder from the top. My compressor is a band of thin gauge metal that can be contracted or expanded using a wrench so it fits a range of piston sizes. There is a small lever on the take up reel that loosens the band a bit so the piston is easier to slide out of the band into the cylinder. The bottom of the band has some dimples that help hold the band inside the cylinder while the top of the band is smooth.
I open up the compressor and slide the piston and rings inside being careful not to catch a ring on the edge of the band. Then I use the wrench to tighten the band compressing the rings into the grooves.
I adjust the tightness so the piston just slides when I move the lever that loosens the band. I put the piston skirt into the cylinder and slide it down until the dimples on the bottom of the compressor band fit inside the cylinder.
Then I gently push the piston into the cylinder until the bottom ring touches the top of the cylinder. I gently rock the piston side to side with gentle pressure until the ring slides into the cylinder. The edge of the ring catches the edge of the cylinder a tiny bit and if I just force the piston into the cylinder I will break the ring. I continue this technique for the middle and top piston until I have the piston and rings inserted into the top of the cylinder. I remove the ring compressor and push the piston through the cylinder until the holes for the wrist pin are showing at the bottom of the cylinder.
Oiling Cams, Followers, Connecting Rod, Piston Skirt
I used the engine assembly lube and a toothbrush to get it on the cam lobes.
I put some on the cam followers and the dimple on the top of the follower where the push rod rides. I used it on the push rod ball ends.
I oiled the main journal bearings and I put two drops of oil on the piston skirt and spread it across the skirt with my finger
Apply Gasket Cement
I’m ready to apply the gasket cement on the base gasket, the cylinder base and the engine case. The idea is to apply a uniform, light layer of cement on these surfaces. I use Acetone to clean all these surfaces so the cement will stick well.
I heat the Hylomar in front of my workshop heater and then put it in glass of very hot water to keep it warm. This helps keep it fluid so I can get a thin even coat.
I start with the engine case and get a uniform coating including around the cylinder studs using my finger to[ to smooth out the cement.
I coat one side of the base gasket and install it with the coated side facing the engine case. I’ll coat the other side of the base gasket after I get the wrist pin installed on the piston.
I coat the base of the cylinder.
Install Push Rod Tube Rubber Gaskets
I put the push rod tube rubber gaskets on the push rod tubes on the bottom of the cylinders. The rubber gaskets have a top and bottom. The bottom has a vertical line from the mold and is wider than the top.
The ridges on the outside of the rubber gasket fit into the engine case as shown here.
The gaskets need to slide on the push rod tubes which move as the tubes heat up. I put a light smear of silicone grease on the inside of the rubber gasket and then put them on the push rod tubes.
Then I oil the ridges on the outside of the push rod tubes.
Installing Cylinder and Wrist Pin
I’m ready to put the cylinder on the engine by sliding it on the four cylinder studs. To make it easy to slide the wrist pin through the piston and connecting rod bushing, I freeze the wrist pin for several hours. It is secured by two C-rings that go into grooves in the piston wrist pin holes.
I put rags in the engine case around the connecting rod so it is supported. I slide the cylinder with the piston sticking out of the bottom on to the cylinder studs. Then I make sure the arrow on the top of the piston is pointing to the front of the bike and gently slide the cylinder and piston down the cylinder studs. I guide the connecting rod inside the piston and align the connecting rod bushing with the wrist pin holes in the piston. I oil the outside of the wrist pin and then I push the wrist pin into the wrist pin hole on one side of the piston, through the connecting rod bushing until it passes through the other piston wrist pin hole. I center the wrist pin on the connecting rod so it doesn’t cover the grooves on either end of the wrist pin.
I make sure rags fill the hole in the engine case because putting the C-ring into the groove will take several tries with the C-ring flying out of the wrist pin hole when I can’t quite get it to seat. I don’t want it fly into the engine 🙁
I put one end of the C-ring into the groove and with a pair of pliers I bend the other end of the ring down and toward the groove forcing more of the C-ring into the groove until I get to the end of the C-ring where I use the screw driver to push the end inside the wrist pin hole and then back inside the hole until it to seats into the groove. The 6th time, it seats correctly :-). Then I put the another C-ring into the other wrist pin hole.
Now I put the Hylomar on the top side of the base gasket and I’m ready to push the cylinder toward the engine.
I make sure the transmission is in 2nd gear so I don’t turn the crankshaft as the piston is pushed up the cylinder. I make sure the push rod tube rubber gaskets are aligned correctly.
Then I slide the cylinder toward engine and align the push rod tube rubber gaskets into the holes in the engine case. I want them to be aligned in the holes, but they won’t be fully seated yet.
Install the Head Gasket, Head and Rocker Arm Assembly
At this point the cylinder is still loose but close to the engine block with the base of the cylinder inside the hole in engine case. I install the head gasket being sure the printing and the blue rings around the holes face me. At the bottom with the holes for the push rods, I make sure the hole in the gasket lines up with the hole in the cylinder and does not obstruct any part of the hole. If the gasket is installed backwards, the push rod tube holes in the cylinder are obstructed by the edge of the holes in the head gasket.
When I removed the rocker arms and push rods, I labeled them so they I know which are the left and right side and which are exhaust and intake.
There four dark colored nuts with a boss on one side secure the rocker arm assembly on the cylinder studs in the head and also to tighten the head and cylinder onto the engine block. The boss goes against the rocker block.
There are two thick washers with nuts that are used to secure the head to the cylinder using the short studs in the cylinder at the 12:00 and 6:00 positions.
The head has a mark indicating if it is left or right (shown) and of course, the spark plug hole goes on top and the threaded spigot for the exhaust pipe is on the front. I use the left head as I’m assembling the left side first.
Some heads use an O-ring under the rocker block and some don’t. Bob’s material has a picture of both style heads. My heads have the passage for the cylinder studs enclosed in the aluminum casting, so I DON’t need the O-rings. You can see the cast aluminum cylinder behind the metal pin through the cooling fins in the picture below.
I insert the push rods into the tubes and make sure they are in the indentation in the top of the cam follower.
I use the rocker arm nuts to help draw the cylinder and head down to the engine case but I don’t install the rocker arms yet.
I want the cylinder to be drawn evenly into the engine and not get it cocked to one side. I tighten each of the four nuts in a cross wise pattern about 3/4 of a turn on the bottom nuts and 1/2 turn on the top watching the base of the cylinder and adjusting how much I turn each nut so the cylinder is drawn into the engine case evenly. There is resistance from the push rod tube rubber gaskets so the cylinder tends to get cocked if you aren’t paying attention.
I keep an eye on the push rod rubber gaskets and when they are fully seated I stop.
I see that the cylinder is uniformly snug against the engine case with a small amount of gasket cement squeezed out around the base gasket.
I remove the rocker arm nuts from the cylinder studs so I can install the rocker arms. Each of the arms has a block at the top and bottom. The top block has a disk in the center while the bottom block doesn’t. Each block is split with a cut on one side. The cut faces toward the outside of the head.
It’s important to install the rocker arms with the top block at the top and the split in the blocks facing to the outside of the head as shown below.
I put the four rocker block nuts on the cylinder studs and tighten them to just snug (maybe 5 FOOT/pounds) while pinching the top and bottom blocks of the rocker arm assembly together. I want the rocker arm to rotate easily but I don’t want the arm to be able to move up and down. Based on Oak’s guide, I want the push rods to be vertically just above the center line of the push rod tube holes and horizontally in the center of the hole to prevent the rods rubbing on the inside of the tubes. Oak provides an extensive and detailed description of precisely aligning the rocker arms and push rods in an addendum included at the back of his top end reassembly guide.
Here is the proper orientation of the split in the block and the rocker block nuts as seen from the front. The split faces me and the boss on the nut is against the face of the rocker block.
Then I install the large washers on the short cylinder studs at the 12:00 and 6:00 positions. The washers have a beveled edge on one side that faces you.
The holes are deeply recessed in the head. I use a magnetic telecoping rod to push the washer into the hole on the stud and then hold it with a finger as I remove the magnet.
To get the nut to start on the stud, I use the magnet to hold it in place, put a finger on the nut and remove the magnet and then with the tip of the finger on the face of the nut, I spin it a 1/2 turn or so to get it threaded. I use a socket with extension to get it snug.
Oak provides measurements to help align the rocker blocks. These are based on the thickness of the blocks which can vary. The “standard” width is 22 mm which is what I have went I measure mine.
Oak provides a table for the distance between the inside and outside faces of the rocker blocks. I adjust the blocks with the nuts snugged up lightly tapping on the blocks with a rubber mallet. For the 22 mm wide blocks, I want 71 mm distance between the inside faces of the blocks while I ensure the push rods stay in the correct orientation.
Torquing the Head
Their are six nuts to torque: the four rocker arm nuts and the two nuts on the short cylinder studs at 12:00 and 6:00. The head is torqued down in stages and in a cross wise pattern. Facing the head, the six nuts layout in a 12:00, 2:00, 4:00, 6:00, 8:00 and 10:00 position. The sequence I tighten the nuts in is 2:00, 8:00, 4:00, 10:00, 6:00 and 12:00. The stages I tighten the nuts are 10 FOOT/pounds, 15 FOOT/pounds, 20 FOOT/pounds, 27 FOOT/Pounds.
As I increase the torque, I make sure the push rod is not moving in the tube and there is no vertical movement of the rocker arm and the rockers still rotate easily. I’ll let the head sit over night, check the torque again and then set the valve clearance.
When I’m done, I use some Acetone to clean up the little bit of gasket cement that has squeezed out around the base gasket and put an old spark plug into the hole and clean shop rags into the intake and exhaust spigots to keep anything from getting into the cylinder.
Here is the left side top end assembled. I put the valve cover on just to show how it will look, but since I need to set the valves after rechecking the torque the next day, I didn’t tighten the cover yet.
And, here is what I started with just about a year ago. Not a lot of difference except for the missing barn straw. 🙂
Installing the Other Side
Now, I carefully use the rear wheel to bump the engine until the “OT” mark on the flywheel is again centered in the hole so the right side is on the compression stroke. And I repeat the procedure on the right side. Here is the right side installed.
Here is the final result with the top end assembled with new spark plugs that I set to 0.025 inches of gap.
I’ll add the exhaust, carburetors and cables later and I’ll document that in another write-up.
2017-04-30 Note about Oak Okleshen passing away.
2017-12-22 Correct error of Top Dead Center identified by “S” mark, it’s the “OT” mark, of course.
Pingback: 1973 BMW R75/5 Rebuild: Install Engine Top End | Motorcycles & Other Musings
I’m sure many, many of us appreciate your good documentation and pictures. Makes me BOLD ! Hey, I could do this too.
The nice thing about airhead top ends is that they are pretty simple to work on. The only special tool that I would recommend is the vernier caliper to get the rocker arm spacing correct, but a decent one is less than $50. So, get BOLD 🙂
Just want to drop a note and say your site is beyond helpful. I haven’t even started to really tear into my 78 r100/7 and 78 r80/7 and i already feel like i know the bikes based off your blog and photos. Thanks again!!!
Thank you very much for the kind words. Your comment about what the content has done for you is exactly what I am trying to achieve.
Best of success on your airhead project. It is always cool to hear from someone invested in getting or keeping one of these machines on the road.
Thank you so much for posting Brook. My 75/5 is just starting to smoke a little on the left side and I am planning on doing the cylinders and heads next winter. Your descriptions and pictures will be very helpful. Ben Zehnder, Orleans, MA
Thanks for visiting. I’m pleased that this material will help you keeping your R75/5 running well.
Hi Brook, I am beginning to put my 74 R90S back together after stripping it down and painting the frame. Besides cleaning and new parts as nessasary I did the top end with 1st over rings, valve job and new pushrods and seals. I am reviewing your blog every step of the way. Your blog is excellent, and I thank you for the time and effort you put into it. Big Thanks, Richard
I’m pleased to hear this material is helping you with your R90S project. Should you need an “independent road test in the Colorado mountains”, don’t hesitate to drop the bike off at my place :-).
Wow what a great article. I have become the owner of a 72 R75/5 with about 30,000 miles on it and has set for many years. It seems to be free. Do you think I should tear it down anyway? Any advise?
Thank you for the kind words. To the question of “Do you think I should tear it down anyway?”, it depends. If the bike runs well, has good compression, passes a leak down test, idles well and smoothly accelerates, does not have oil leaks around the front cover (leaking front crankshaft seal), the rear of the engine where the transmission mounts (leaking rear crankshaft seal), the clutch works smoothly, the front forks aren’t leaking, and the steering head bearings are smooth when you move the handlebars lock-to-lock, then there’s nothing to worry about that routine maintenance won’t fix. If any of the above is evident, then you can correct whatever is wrong without doing a complete tear down.
That said, if the idea of doing a tear down, a new paint job for the frame, tank, and fenders, and replacing engine seals, oil pump cover and seals, doing a carburetor rebuild, etc. appeal to you, then why not? Well, one answer is the cost of “preventive maintenance” all at once, and the time the bike will be unavailable for riding.
I hope the above is helful.
I have no formal mechanic training, but have been able to follow your instruction to:
set valve gap clearance
replace front and rear brakes
replace front brake cable
rebuild both carbs
Next on the agenda is to replace push rod gaskets, top end gaskets, oil pan gaskets. It is a 1970 R75/5.
Cool beans. You are taking on, and completing, a lot of the routine items necessary for the “care and feeding” of an airhead.
I have installed right side top end successfully and am moving to the other side.
Why do you bump the timing mark to “S” rather than “OT” to install the other side?
Thanks / Dennis
Short answer: I made a typographical mistake. Thanks for catching it. I’ve made the change.
Thanks for the clarification.
Your documentation has been invaluable in my undertaking of the restoration of my ‘71 R75/5.
Going down the backstretch after 2 years and I’m getting excited to wrap it up by Spring.
Regards / Dennis
Thank you so much for this entire series. This is my first Airhead. 1973 r75/5. In your opinion could someone rebuild the entire engine and transmission with the Cycle Works tools.
Thank you for leaving this comment. I want to separate having tools from having experience and skills. All three are necessary to completely rebuild an engine. I have slowly gained some experience and skill over the past 12 years of progressively rebuilding four bikes. On each project, I took on one or two projects to expand my experience and skill. That said, there are skills I lack and for that work, I have professionals do it.
Among the higher skill and experience work is transmission rebuilding. Right behind that is crankshaft main bearings followed by connecting rod bushings. I would also put rear drive rebuilding in the category requiring high skill and experience. In all those projects, significant experience is important to a happy outcome.
So how do you get experience? Well, you do the work, of course, but its helpful to have advice from professionals and very experienced amateurs to guide you. I rely on the micapeak airhead list to get reliable answers to my questions along with expert advice. If you haven’t joined it yet (it’s free) click here and climb on board.
I hope this helps.
I will join and thank you.
I retired from Delta Airlines after 30 years as an Aircraft Mech. I have my A & P license. I have work many years in the engine shop and in the hangar. For the past 10 years I have worked at Lockhead Martin. Most recently building the F35. You are right about knowing the tricks of the trade and the right way to do the job. I have my first order in to Cycleworks. Just wondering if an engine and transmission can be rebuilt with Cycleworks tools. I have rebuilt many motorcycle engines but this is my first BMW. I would love to meet you someday.
Well, you have far more experience and skills than I do. 🙂
The cycle works engine tools will allow you to replace the main bearings, but not the rod small end bushing which requires reaming. The transmission tool-measurement plate-is just the beginning of what you need if you are going to replace the seals and bearings. There are some special tools that I use to do that work that I borrow from a long time retired airhead mechanic. You can see what goes on with the transmission and what the other tools look like in these documents on my site:
-> 23 BMW 1977 R100RS Remove, Disassemble and Inspect Transmission
-> 23 BMW 1977 R100RS Transmission Refresh and Assembly
I hope that helps.
Thank you sir
I hope this note finds you well. I was able to complete the r90s rebuild that I have been working on. The project has consisted of a complete rebuild due to the broken rod which punctured the crank case.
The good news is it fired right up, and the top end seemed to function as it should.
the bad news is I immediately had a considerable leak from either the rear main seal or the oil pump.
I replaced both the o ring in the oil pump and the rear main seal, however i did not replace the oil pump cover as i just used the one off my old engine, which inspection showed me was functioning as it should.
the “donor” crank case did have quite a bit of gasket sealant around the oil pump, so i figured my oil pump cover would fix that problem, but now I am worried that the donor case has a problem with the oil pump on the crank case side, and not the cover side…
so i am at a crossroads, my first inclination is to buy the “new style” oil pump cover with the recessed bolts (you may remember my previous mistake using the square bolts on the old style oil pump cover, thus jamming my fly wheel) and hoping this fixes the oil leak.
from inspecting the area after the short run, I cannot clearly tell where the oil is coming from but it has splattered up the inside of the flywheel so i assumed it is squirting out from the oil pump.
or i may have messed up my rear main seal during install.
any advice or guidance that may help me assess my situation would be appreciated.
If it was my bike, I would go back in to investigate what’s going on. I would verify the clutch plates didn’t get oiled. I would replace the old style cover with the new that uses the hex bolts. As I took things apart I’d look for the oil leaking from the oil pump cover and/or from the rear main seal. That maybe difficult due to the ail getting thrown around. It I couldn’t make a positive determination, I’d clean inside the bell housing to remove all the oil. Then I’d try cranking the engine with the transmission removed and see if I find any oil leaking from the main seal or the new oil pump cover with new O-ring.
I hope that helps.
very helpful. great idea cranking with trans removed. hadnt thought of that…. no harm in doing it. i think the amount of oil that leaked in the very short amount of time i ran it (about 20 seconds) would make me think it is the main seal. in inspecting the oil pump cover, unless that generates a high amount of pressure, i cant see that much oil leaking from that small of a gap… i would assume oil pump leaks would weep and not “run” this was a steady leak of oil…
as far as cranking with trans removed, should i install the clutch or just the flywheel?
and thank you for your suggestion… very helpful to diagnose before i run to the parts store.
best, and happy labor day.
Just try the flywheel and leave the clutch off.
Thank you Brook.
question about stretch bolts. i have purchased new sets for crank / clutch / driveshaft, even though the other ones are brand new, they were torqued prior to the engine leak.
i am questioning the pros and cons of installing the new rear main seal, the new oil pump cover and testing these parts with old flywheel bolts or use the new set… and risk having to buy a third set if the engine leak is not fixed with these two new parts…
any thoughts on reusing the old crank bolts for a quick test or is the real danger in them snapping during the torque to spec…
thanks in advance,
If the bolts are the older 10 mm bolts (part# 11 22 1 257 796) then I would replace them. It they are the newer 11 mm bolts (part# 11 22 1 262 060), I would reuse them.
The clutch bolts are not stretch bolts. The four drive shaft bolts are reusable, but I always use the newer slightly shorter ones that do not require the lock washers (part# 26 11 1 242 297).
I hope this helps.
also, i cannot think of any other source of the oil, other than the rear seal or the oil pump cover and if these two parts dont fix the problem, then my bell housing would be the only other culprit and in that case I am in trouble 😉
Just stay focused on your initial hypothesis until you prove it right, or wrong. It’s easier that way and helps me stay focused on what I need to do. 🙂