- Remove Connecting Rod Bolts
- Inspecting Connecting Rod Bearings
- Measure Connecting Rod Journals
- Preparing The Connecting Rods
- Install Connecting Rods
Since this bike has over 64,000 miles on it and sat for over 25 years, I want to replace the connecting rod bearings. I did find water in the crankcase when I drained the oil, which can damage the rod bearings. I’m hopeful I won’t find significant damage to them, but you never know until you take a look.
To get to the rod bearings, I remove the top end of the engine. You can read about how I do that here:
The crankshaft, connecting rods and connecting rod bearings in the 1983 R80ST are the same as the ones used in the 1983 R100RS I previously rebuilt. So I’m going to reference sections of the documents I posted about removing and installing new connecting rod bearings in the 1983 R100RS.
The rod bolts are “use once” as they are designed to stretch when installed and cannot be reused. The bearing shell comes in two pieces per connecting rod, so I need four of them. Euro MotoElectrics supplied all the parts for this charity rebuild project at no cost. EME provides a set of four bearing shells as a single part number, EME Part# CSBearing460.
|11 24 1 258 460||BEARING SHELL, Standard Size||4|
|11 24 1 337 553||CONNECTING ROD BOLT||4|
The connecting rod is secured to the crankshaft with two special bolts. They are designed to stretch when torqued, so they are “use once”, and they have a special head requiring a 10 mm “serrated wrench” I got from my local NAPA store, Part# SER 2305, for about $11.00.
I use a 13 mm socket and slip it over the head of the serrated wrench so I can use my breaker bar to loosen the rod bolts.
I use my long socket extension and a breaker bar to loosen the bolts. The long extension allows the breaker bar to clear the cylinder studs protruding from the engine block.
Here is a short video summarizing how I do the work on the 1983 R80ST.
VIDEO: 1983 BMW R80ST Replace Connecting Rod Crankshaft Bearings
Remove Connecting Rod Bolts
This link shows how I did this on the 1983 R100RS.
As was the case on the 1983 R100RS, I had to use a flat screwdriver blade on the lip of the connecting rod back shell and tap it to get the rear shell to separate from the connecting rod. Here are some pictures from the 1983 R80ST.
Inspecting Connecting Rod Bearings
The connecting rod and the rear shell have bearings inserted. Unlike the ones on the 1983 R100RS that had a lot of scoring due to the oil filter high pressure valve having come apart allowing dirty oil to circulate, the R80ST bearings are in good condition. There is one score in the left side bearings, but they look to be in good condition.
Measure Connecting Rod Journals
I use a 1-to-2 inch micrometer that can measure to one ten-thousandth (0.0001) of an inch to measure the diameter of the connecting rod journals. I use a one inch gauge block to calibrate the micrometer. I find that it is long of one inch by 0.0002 inches, so I will subtract 0.0002 inches from my raw measurements to get the final corrected measurement.
As shown in the picture below, the horizontal line on the micrometer is just above the “0” line on the barrel which means the micrometer measurement of the gauge block is a bit longer than 1 inch.
I look for the vertical line on the barrel that aligns with one of the numbered lines at the bottom. Since it’s the line with “2” at the bottom, the micrometer is off by 0.0002″, or two ten-thousandths of an inch.
I note which micrometer I use. I note the acceptable “range” of connecting rod journal diameter, 1.8888-1.8894 inches. I also note the error in the micrometer reading when I calibrated it. In this case, the micrometer reads 0.0002 inches longer than it should, so I will subtract 0.0002 inches to the raw measurements to get the corrected measurement.
How To Take The Measurement
Here is how I determine the diameter of the crankshaft connecting rod journal. I set the micrometer to about 1.9 inches which is in the range of the journal diameter. Then I slowly tighten the micrometer using the clutch as I move it up and down against the journal feeling for the tight spot. I keep doing this until it feels like I am against the tightest spot and then tighten the clutch until it clicks. Then I push the locking lever and remove the micrometer to take the reading.
How To Read The Micrometer
The following three pictures show how I read the measurement from the micrometer. First I note how many tick marks are exposed past the “8”. Each is 0.025 inches, or 25 thousandths of an inch. And, since this is a 1-to-2 inch micrometer, the “0” is at 1 inch, so I record 1.875 for the micrometer value in the spreadsheet.
The horizontal line is between the “14” and “15” marks on the barrel, which means the measurement is somewhere between 0.014 and 0.015 inches. I record the lower value, 0.014 inches for the Barrel in the spreadsheet.
The last value is the Vernier on the micrometer. I look for the value at the bottom whose vertical line matches one of the numbers on the Barrel. In my case, that’s “4”, which means 0.0004″, or four ten-thousandths which I add for the Vernier in the spreadsheet.
Recording Measurements In Spreadsheet
Below is a picture of the spreadsheet I use to record the measurements and to compute the final, corrected value of the crankshaft connecting rod journals.
At the top, I note which micrometer I use. I note the acceptable “range” of connecting rod journal diameter, 1.8888-1.8894 inches. I also note the error in the micrometer reading when I calibrated it. In this case, the micrometer reads 0.0002 inches longer than it should, so I will subtract 0.0002 inches from the raw measurements to get the corrected measurement.
The “Mic” column records the micrometer reading. The “Barrel” records the barrel reading and the “Vernier” column records the Vernier reading. The “Raw” column sums the three readings and the “Corrected” column adds in the “Calibration” correction of -0.0002 inches.
I average the three Corrected values and use that as the measured value of the diameter of the crankshaft connecting rod journals.
I found both journals were 1.8892 inches, so there is no appreciable wear on the journals after 64,000 miles. 🙂
Preparing The Connecting Rods
I show how I prepare the connecting rods for installation with new bearing shells in the 1983 R100RS document.
The bearing shells in the 1983 R80ST were in good condition. There was one scratch in the right side bearing shells, but there was no evidence of metal particles having circulated in the oil, unlike what I found in the 1983 R100RS whose oil filter high pressure relief valve had failed allowing unfiltered oil to circulate.
Here are some pictures from the 1983 R80ST.
Install Connecting Rods
Checking If The Connecting Rod Binds On The Crankshaft Journal
As you tighten the connecting rod bolts, check that the connecting rod rotates freely on the crankshaft journal. As I found on the right side connecting rod, mine bound up when I snugged up the connecting rod bolts. So, I did not torque the bolts, but removed them and the connecting rods to try and figure out what was wrong.
I checked that the shells fit the rod and end cap correctly and that the tab on the bearing shells was fully seated in the notch in the rod and end cap. I checked that the rod bolts screwed in easily and found that the bottom bolt got hard to turn but not the top bolt, I could screw in the top bolt by hand, but had to use the special wrench to turn the bottom bolt. Hmmm …
After spending some time trying to figure out what was going on, with no success, I called a friend and independent BMW mechanic, Matt Iles, owner of Iles Motorsports in Denver, CO. Matt is also the one who alerted me to the availability of this R80ST in Clem Cykowski’s estate when I was searching for one to restore and auction for the benefit of the Motorcycle Relief Project.
Matt suggested some things to check, including to look for a burr in the bolt hole in the connecting rod or in the screw threads in the end cap. I found no burrs, He offered to come over and take a look.
Matt figured out the the locating pin on the bottom of the right connecting rod was catching in the hole in the end cap which caused that end of the end cap to not seat flat against the connecting rod. After some playing around, he saw that if he tightened the lower connecting rod bolt first, he could get the end cap to be flush against the connecting rod.
So, he installed the right connecting rod, snugged up the lower bolt first and then the top bolt. The right connecting rod rotated smoothly on the crankshaft journal with no binding of the connecting rod on the crankshaft journal. This was a great learning experience and I really appreciated Matt’s willingness to come over and help identify and solve this problem.
Now, both connecting rods drop under their own weight after the connecting rod bolts are torqued to 36 Ft-Lbs. 🙂