I have a compression test related question. I did a search on the Forum but can't find an answer to my question. Also, part of the question deals with incomplete information in the Service Manual (imagine that)

im going to do a compression test on my 87 FLSTC. The reason is I just want to get an indication how the top end is doing. I have always gotten a little oil out the air cleaner breather hose but just want to verify the rings are still okay. Now on to the question.

The service manual says to crank the engine over 7 times. The manual says to note the compression on the 1st and 2nd strokes but never specifies what to do with the documented compression numbers for the first two strokes. The manual only says that the finished compression for the two cylinders have to be within 10% of each other and above 90 psi.

I'm in no way a mechanic. However, I have done well over the years just using the manual or people's suggestions and doing tests and work on my bikes myself. I have found out many answers to questions about my bikes by searching for answers on this Forum. That's why I finally signed up. So if anybody can educate me what to do with the compression values on stroke 1 and 2 I'd appreciate any help or advice.

Greg M

 

We go 8 complete cranks, throttle wide open with air cleaner off, battery fully charged, and battery charger in place.
Hope this helps.
Scott

 

Follow Scott's procedure and don't worry about the readings from the first cranks; the final reading is the only one you need for a baseline check.

 

Thanks Scott. Good idea about keeping charging in place. My guess is so you get constant cranking speed without any variability between cylinders. After I do the test this weekend and if I end up with poor results, I'll revisit the thread.

Greg M

 

I would decarbon it with seafoam first to get a better reading.