- Top End Rebuild Work
- Install Push Rod Tubes and Cylinder Head Studs
- Install Connecting Rods
- Replace Pitted Cam Followers
- Preparation for Top End Assembly
- Install Pistons in Cylinders
- Install Push Rod Tube Rubbers
- Install Cylinder Stud O-rings and Gasket Sealant
- Install Gudgeon Pin Through Piston and Connecting Rod
- Install Cylinder and Head on Engine Block
- Adjust Valves
Previously, I removed the heads, cylinders, pistons, rings and connecting rods. I installed new rocker arm needle bearings to replace the broken bearing cages. I disassembled the heads and inspected the valves and seats. You can read how I did that work here.
- 11 BMW 1977 R100RS Remove Pistons, Connecting Rods & Inspect
- 11 BMW 1977 R100RS Replace Rocker Needle Bearings, Remove Valves & Inspect
Top End Rebuild Work
I had the Nikasil cylinders replated and honed to match the new high compression (9.5:1) pistons. I had the connecting rods refurbished and I had the heads rebuilt.
Refurbish Connecting Rods
I had the connecting rods inspected and refurbished to ensure they are straight and the big end and small end holes are true and aligned via Tom Cutter at Rubber Chicken Racing Garage.
Tom recommends reconditioning the connecting rods. The big end (crank journal) and small end (gudgeon pin) holes can become oval and the rods can stretch so the hole centers are no longer aligned or the correct distance apart. He has them reconditioned so the rods are true in both planes and the big and small end holes are round with the hole centers at the correct distance from each other.
The reconditioned rods show machining of the end caps so some adjustment was necessary.
New High Compression Pistons and Replate Nikasil Cylinders
I decided to replace the USA stock 8.2:1 pistons that come with the Nikasil cylinders with high compression 9.5:1 pistons available in Europe. Tom recommends having the cylinders replated with Nikasil, not because it is worn or damaged, but to ensure correct clearance between the pistons and the cylinder. He believes the piston manufacturing tolerances do not ensure the proper fit with the cylinder. Since both the cylinder and piston are aluminum, the clearance is very tight, 0.001″ or less. So stripping the Nikasil from the cylinders, honing them to the correct clearance for the new pistons and replating them with Nikasil ensures a correct fit and long engine life.
I was concerned about the exhaust valve seats being original and subject to recession and excessive wear caused by our no-lead gas. Several of the valve faces were worn close to, or past, the minimum face thickness. I had the heads rebuilt with new exhaust valve seats, valves, valve seats, springs and keepers by Randy Long at Long’s Mechanical Services. The new valves and seats were cut and lapped for a gas tight seal.
I use a machinist flat to help set the push rod tube height.
I use a piston ring compressor to install the pistons from the top of the cylinder.
Since the cylinders were bored out, there is no ridge at the top of the cylinder. If the cylinders did not have the top ridge removed, I would not install the rings from the top of the cylinder, but from the bottom. This avoids the possibility of breaking a ring on the ridge.
The connecting rods bolts have a 12 sided head called a serrated head. I got the wrench that fits it at my local NAPA store, a 10 mm wrench. I used a long 13 mm socket and put the serrated wrench inside the socket to torque the rod bolts.
I use an M12 x50 Torx head bolt as a drift to drive the push rod tubes into the cylinder.
These are the parts I used for this work. In addition, Tom Cutter, who had the the head work done, supplied new valves, springs, exhaust seats, valve guides and keepers.
|11 12 1 338 715||CYLINDER HEAD GASKET ASBESTOS-FREE||2|
|11 12 1 338 426||GASKET – ASBESTFREI||2|
|11 11 1 337 567||O-RING – 93X2,2 (from 08/80)||2|
|11 32 1 262 995||PUSHROD SEAL (from 08/80)||4|
|11 24 1 258 460||BEARING SHELL||4|
|11 24 1 337 553||CONNECTING ROD BOLT||4|
|11 32 1 262 638||CAM FOLLOWER (USED)||2|
|11 25 1 337 176||PISTON – 93,98 E=9,5 + (INCLUDES RINGS, GUDGEON PIN, CIR-CLIPS)||2|
|11 24 0 618 100||CONNECTING ROD BUSH||2|
- Robert Fleischer: Replacing Pushrod Tubes & Seals
- Robert Fleischer: Disassembly & Assembly of Heads
- Oak Okleshen: “Manual 1: Boxer Top End Disassembly, 1970-1975” and “Manual 2: Boxer Top End Reassembly 1970-1975” in a single bound booklet. Sadly, Oak died in April 2017, so I don’t have any information about future availability of this booklet
I read through Anton Largiader’s material on rocker arms.
I did this same work on the 1973 R75/5 and you can find that write-up here:
The procedure for the 1973 R75/5 is similar to what I did for the 1977 R100RS, but there are some differences for the 1977 R100RS:
- The rocker arm pillow block was redesigned so it centers on the cylinder studs
- There is no base gasket
- There are two small o-rings that fit on the upper cylinder studs to seal the oil passage along the top studs into the heads. The top cylinder stud holes are machined for these o-rings.
Install Push Rod Tubes and Cylinder Head Studs
To perform the Nikasil plating and machining, the push rod tubes and the two short cylinder studs that help secure the head to the cylinder located at the 12:00 and 6:00 position were removed, so I have to install them.
Install Push Rod Tubes
On the earlier push rod tubes (before 1981 I think), the fork tube rings are a shrink fit and often slipped on the tube. Replacing those tubes makes sense as they will not reliably seal the rubber boot to the engine block. My push rod tubes came with the Nikasil cylinders and have the fork tube ring brazed to the tube and won’t migrate. Mine are in good condition so I opted to reuse them, but it’s common to replace these with stainless steel tubes.
To make installation as easy as possible I heat the cylinders to 275 F for 2 hours prior to installing them. Since the tubes are very thin, I insert a paper towel plug inside the tubes where they mount in the cylinder and soak the towel with water before putting the tubes into the freezer over night. The added mass of the water in the paper towel will help keep the end of the tube cold.
I use an M12 x 15 Torx bolt that fits inside the tube and just covers the OD of the tube as a mandrel.
I pull the hot cylinder out of the oven, and one tube out of the freezer. To help seal the tubes, I apply a thin smear of high temperature RTV to the outside of the tube before driving it into the cylinder. I align the tube in the hole with a few light taps on the head of the bolt and then hit it sharply and watch how far it goes into the hole in the cylinder. I want the top of the ring on the tube to be about 1.75 -2.00 mm below the face of the cylinder block. I use a machinist flat and a Popsicle stick (it’s 2.0 mm) to set the depth.
I could also have used a couple feeler gauges sandwiched to 0.067″, but the Popsicle stick is easier to handle with the hot cylinder. It’s pretty easy to eye ball the top of the push rod ring against the edge of the stick so it doesn’t quite fit over the top of the push rod ring. I checked with my feeler gauges afterward and the tops of the ring are very close to 0.067″.
I can do both push rod tubes without reheating the cylinder. After the cylinders cool down, I put some green wicking loctite along the top edge of the tube where it fits against the hole in the cylinder. The RTV extruded a bit out of the bottom of the tube creating a seal there, so I don’t need to add any loctite there.
Install Cylinder Head Studs
The heads are secured by the four long studs in the engine block that go through the pillow blocks on the ends of rocker arm shafts. There are also two short studs at the 12:00 and 6:00 position of the heads. These two studs are screwed into the top of the cylinders.
I was told the proper way to install these cylinder studs is to use red loctite. I use a Permatex “equivalent”, #27100.
I use both nuts and double them up on each stud so I can turn the top nut to screw the stud into the head.
To install the studs, I put some red loctite on the threads and screw the stud in using the doubled top nuts. I use a depth gauge set to 28 mm to measure the height of the stud above the top of the cylinder and stop tightening them when the exposed stud is 28 mm above the head gasket flange.
A little loctite pools above the threads and I remove all of it with a shop towel so the head gasket will fit flush on the top of the cylinder.
Install Connecting Rods
Since the bearing shell in one of the rods was scored, I installed new standard size bearing shells. Here (left to right, top to bottom) are the rods, the two bearing shell halves that fit into the big end, the deep 13 mm socket, the special 12-point serrated wrench that fits into the 13 mm socket, the new new rod bolts and moly-graphite assembly lube.
The bottom of the rod has two locating pins on one side that fit into the end cap. The side of the rod with the pins faces to the front, so I mark the small end with an arrow so I don’t install them backwards. When I removed the rods, I marked them and the end caps “L” and “R” so I would install them on the same crankshaft journal they came from.
The bearing half shells have a locating rectangular pin that fits into a corresponding notch in the rod big end and the end cap.
I install one half-shell by putting the rectangular pin into the notch in the rod big end so the edge of the shell is flush with edge of the rod flat. Then I push down on the other end to seat the bearing into the bore. I make sure the ends of the bearing are flush with the edge of the rod big end.
The same procedure installs the other half-shell into the rod end cap.
Here are the rod and rod end cap with the new bearing half-shells installed.
I coat the bearing surfaces with the moly-graphite assembly lube. Then I liberally coat the bearing shell with motor oil and also liberally coat the crankshaft journal with oil.
The new rod bolts should be shiny with no rust anywhere.
Never use rod bolts more than once. When they are torqued they stretch and can not be used a second time without risk of failing.
I put some 3-in-One oil on the threads of the new rod bolts and the threads in the rod end cap.
When I install the rods on the crankshaft journals, I verify the rod is for the correct rod journal and the rod is oriented with the correct side facing forward.
I start by inserting the end cap and holding it onto the backside of the crankshaft journal with one hand.
In retrospect, it would be a good idea to put a rag or two under the crankshaft journal so it you drop the end cap you won’t have to fish it out of the oil pan with a magnet.
Then I install the rod so the pins on the end fit into the holes of the end cap and finger tighten one rod bolt to loosely to secure the rod to the end cap.
I put a shop rag under the connecting rod so I don’t nick the engine case and then I insert the top rod bolt and finger tighten it.
I use a long socket extension to snug up the rod bolts evenly in an alternating pattern until they just become snug.
I secure the rod using wire so it won’t drop onto the engine case and nick it when I torque the rod bolts.
I back off the rod bolts a quarter turn and then use the torque wrench to tighten each bolt in one smooth motion to 36 FT-Lbs.
Replace Pitted Cam Followers
I found the left side intake and exhaust cam followers had pits. Inspection of the cam lobes did not show damage or pitting. I’ve found rust in various places during this project. I suspect these pits were caused by corrosion.
The right side cam followers are fine.
I got two used ones from Matt Parkhouse and lubed them with engine assembly lube and oil.
Preparation for Top End Assembly
I layout the parts I need to assembly the top end. Here are the new gaskets and the push rod tube rubbers.
starting in 1976 when the engine block cylinder bore was increased to 99 mm, the engine no longer has a base gasket.
I use engine assembly lube, silicon grease, Suzuki 1207B sealant and engine oil to prepare the parts for assembly.
I layout the parts for one side at a time as shown below.
In the picture above, left to right, top to bottom: left intake rocker assembly, long cylinder stud pillow block nuts, push rod tube rubber seals, top cylinder stud oil seal o-rings, intake and exhaust push rods (tape is on top end of rods), exhaust rocker assembly, long cylinder stud pillow block nuts, and the new head gasket.
Below is the piston with the rings installed. I received the pistons back from Tom Cutter who installed the rings. His advice is to minimize the number of times the rings get flexed so he installs them once and leaves them on the pistons when he ships them back. I marked the crown of this piston with the side (R-Right) and an arrow pointing to the front where the stamped arrow with “Vorn” was pointing so it’s easy to see which is the front of the piston when assembling the top end.
I also mark the cylinders with the side they go on.
The picture below shows the left cylinder, but of course I used the “R” cylinder with the “R” piston during assembly. I guess didn’t take a picture of the right cylinder marking.
Below is the gudgeon pin (wrist pin) with cir-clips, one is installed on the pin and the other is installed after the pin is inserted through the piston and rod bearing. I freeze the pin prior to installation so it will slide easily through the holes in the piston and the rod bushing.
Install Pistons in Cylinders
I prepare the cylinders with two drops of oil on my finger that I wipe around the inside walls of the cylinder. I want a light film but not too much oil on the wall. This will help the rings bed into the cross hatching of the cylinder the first time the engine starts.
I install the piston ring compressor on the pistons and compress the rings using the square wrench supplied with it to tighten the compressor band. The small lever on the cylinder can be used to slightly loosen the band to help slide the piston out of the compressor into the cylinder. I didn’t need to use it to slide these pistons into the cylinders.
If the piston starts to slide out of the compressor band when you push it with your hand and then stops, a ring is catching the edge of the cylinder. DON’T FORCE IT OR HIT THE PISTON WITH A HAMMER. I had to remove the piston a couple times and tighten the band again paying attention to where the edges of the band over lap and ensuring the edges lined up. That seemed to help keep the rings fully compressed and avoid catching on the edge of the cylinder. If you force it you can break a ring.
Install Push Rod Tube Rubbers
The push rod tube rubbers are oriented on the push rod tubes so the vertical line on the outer edge of the rubber points to the bottom. The hole in the rubber seal the push rod tube slides into is off center to accommodate the angle of the tube to the engine block. If you install the seal upside down (line pointing up) it will split.
The push rod tube rubbers must be able to move as the cylinder heats up and cools down or the rubbers won’t seal and leaks will develop. I use a small dab of silicone grease on the inside of the rubber and then slip them over the push rod tube. I put a couple drops of engine oil on the outer ridges of the rubber seal that slide into the holes in the engine block.
Install Cylinder Stud O-rings and Gasket Sealant
The Nikasil cylinders have a groove in the top holes for the top cylinder studs. The holes hold a small rubber o-ring to help seal these holes. The top cylinder stud passages in the cylinder deliver oil to the rocker assembly in the heads which drains back to the oil pan through the push rod tubes. They also have a large groove in the bottom sleeve for the large o-ring to help seal the cylinder in the engine block.
I clean the sealing surface of the engine block and the cylinder base with acetone to remove any traces of dirt and oil.
Then I sparingly apply the Suzuki 1207B sealant on the cylinder base and then spread it evenly in a thin layer with my nitrile gloved finger. I’m careful to keep it out of the o-ring groove on surrounding the top two cylinder stud holes that are on the left side of the cylinder in the picture below.
Then I put a tiny dab of silicone grease on the two small o-rings that fit over the top cylinder studs to help keep them in place being careful not to get any on the sealant. I install the large o-ring in the groove of the cylinder base being careful not to disturb the sealer on the cylinder base.
Then I apply another thin coating to the engine block and move the o-rings out of the way as I apply it so they don’t get any sealant on them. Again I am careful to keep the sealant out of the area where the o-rings go so it won’t obstruct the oil flow around the top cylinder studs.
I slide the correct cylinder with the piston inside on the four long cylinder studs. I make sure the piston is oriented with the arrow I drew facing forward.
These Nikasil cylinders have small “L” and “R” stamps on the bottom of the cylinder casting.
Install Gudgeon Pin Through Piston and Connecting Rod
It’s easier to install the pin if it’s put in the freezer for 30 minutes to shrink it. It should slide in smoothly.
If the gudgeon pin won’t slide smoothly through the piston bushing, there could be a burr on the bushing. You can polish the edge of the piston bushing with 600 grit paper and then clean completely with solvent and paper towels. Then try inserting the pin again. If it still hangs up the piston bushing, you can use a heat gun to warm that area to expand it. The combination of a frozen gudgeon pin and hot piston bushing should have sufficient clearance to push the pin through.
Before I slide the piston over the end of the connecting rod I oil the rod bushing with engine oil. Then I slide the cylinder toward the engine block carefully until the connecting rod slides between the bosses in the piston.
I pull the frozen gudgeon pin from the freezer and insert it through the piston boss and gudgeon pin until the cir-clip on the pin is against the piston boss. The groove for the cir-clip on the on other side of the gudgeon pin is now available to install the second cir-clip
The cir-clip has a side with a sharp edge and a side with a rounded edge for the hole the pin goes through. When I install the them, I put the sharp side facing outward. In the pictures below, looking at the hole toward where the tabs with the pin holes for the pliers are, you can see the edge of the hole is rounded on one side and sharp on the other.
I install the other cir-clip on the gudgeon pin with snap ring pliers. When the cir-clip is in the groove on the end of the gudgeon pin, I make sure it is seated in the groove by spinning it with a screw driver.
Install Cylinder and Head on Engine Block
Now I make sure the push rod tube rubbers are correctly aligned before pushing the cylinder carefully toward the engine block until the rubber seals just fit into the holes in the engine block. There is a small gap between the cylinder base and the engine block at this point.
The rubber seals may interfere with the frame tube. Rocking the cylinder toward the top will help them pass over the tube. However, this can cause the seal to rotate on the push rod tube, so confirm the line on the rubber seals is still centered and pointing down.
Install Head Gasket, Rocker Assembly and Push Rods
The head gasket can be installed backwards as shown below so the holes at the bottom of the gasket don’t align with the push rod tubes and the push rods will rub on the edge of the gasket.
The correct orientation of the holes will not cover any portion of the push rod tubes.
The head slides on the four long cylinder studs with the threaded exhaust spigot facing forward.
I put some engine assembly lube on the balls on the ends of the push rods and insert them into the push rod tubes.
It is possible for the lower ball to not seat into the recess in the cam follower. So I look to be sure the lower ball is centered on the cam follower.
Then I put each rocker assembly on the upper and lower cylinder studs. I make sure the rocker shaft end with the three rectangular indents around the circumference of the shaft is on top and the split in the pillow blocks is facing to the outside. I install the nuts so the small ring on one face is against the pillow block and flats face outward.
Before I tighten the cylinder nuts I make sure the ball on the end of the push rod is seated in the cup on the end of the tappet adjusting bolt in the rocker arm.
I tighten the nuts carefully so I pull the cylinder evenly toward the engine block. There is resistance from the push rod rubber seals as they are drawn into their holes so I tighten the lower nuts a bit more than the upper ones so the cylinder won’t get cocked.
I stop when the cylinder is just snug against the engine block.
Torque Cylinder Stud Nuts
I insert a large washer on the two short cylinder studs at the 12:00 and 6:00 position of the head, The washer has a beveled face that goes against the face of the nut and a flat face that goes against the head.
I torque the head down in stages: 10 FT-Lbs, 15 FT-Lbs, 20 FT-Lbs, 23 FT-Lbs and 25 FT-Lbs. The pattern is the top left nut, bottom right nut, bottom left nut, top right nut, 6:00 nut and 12:00 nut.
I let the heads sit over night and then retorque them to 25 FT-Lbs again. They will compress the head gasket and loosen so they need to be torqued the next day before setting the valves.
Here is the engine with the top end assembled.
After I re-torque the heads to 25 FT-Lbs, I can adjust the valves. I use a looser intake adjustment of 0.006″ instead of the published 0.004″ for the intake and 0.10″ instead of the published 0.008″ when I install rebuilt heads. I will check the valve clearance at 100, 500 and 1,000 miles and it they are holding steady, I will set them to the standard 0.004″ inlet and 0.008″ exhaust clearances from then on.
I want to remove end play of the rocker arm between the pillow blocks of the rocker arm shaft. I don’t want the rocker arm assembly to be loose enough that I can move it up and down between the pillow blocks. I work on one valve at a time loosening the two nuts that secure its rocker arm. I squeeze the top and bottom pillow blocks until there is no play in one rocker arm and tighten the nuts and then torque them to 25 FT-Lbs.
Then I do the same for the other rocker arm assembly, loosening it’s two nuts and removing the end play in the rocker arm.
I rotate the engine until the “OT” mark aligns with the reference notch in the timing inspection hole on the left side engine block. I try to spin the push rods in the head on one side and the other. One side should allow me to spine the push rods and that’s the side I can set the valve clearance on as the push rods are off the high part of the cam and on the base circle.
To set the valve clearance, I loosen the lock nut on the threaded end of the rocker arm bolt that sits on top of the push rod. I use a feeler gauge to set the clearance between the tappet arm and the valve stem. I like to use the next larger feeler gauge and if it won’t fit but the correct size one will, the clearance is good. I tighten the lock nut and recheck the clearance to be sure it didn’t change.
When I’m done on one side, I rotate the engine one revolution until the “OT” mark is again visible in the timing hole and adjust the valves on the other side the same way.
I put the valve covers on loosely to protect the rocker arm assembles. After I fill the crank case with oil I want to crank the engine to verify oil flows from the splits in the top pillow blocks before I start it. But I won’t get to a first engine start for awhile yet.