I was told today by my HD mechanic that the compression of both front and rear is 210. He told me that normal is around 150. He is going to contact HD and find out what the plan of action should be. He thinks that the pistons and rings need to be replaced. Since the bike is under warranty, I am not worried. I have been having trouble starting the bike after it is hot, and after running a bunch of tests, he discovered this issue. What causes compression problems?

 

Is that really that much higher than normal?

 

Yes. I do not know what the numbers really mean, but he stated he never seen the compression, in both front and back, so high.

 

If it was me I would look at the cams before the pistons and rings.

 

go with mike07 have the cams checked first....and your rocker arms

 

At 210 PSI, a match a good cam to that and you'll have a great running machine on your hands.

Hard hot-restarts are a real pain in the ***, compression releases will fix that.

Steve

 

Your HD mechanic is no mechanic. If the rings were bad you would have lower not higher compression. If anything your something in your valve train is screwed up and not opening the valves soon enough. Could even be the oil pump not making enough pressure/volume to keep the lifters operating properly. When did the hard starting begin??

 

This is definately not a piston/rings issue. If they were faulty in any way, you would have the opposite.....low compression. Unless there is so much carbon build-up it is raising the compression. I doubt it. Both Cyls are the same. 210 is what I like to see with the builds I do, it's high for a stock motor. A leak down test will confirm that too, and would be mandatory in this troubleshooting sequence. You would think qualified personel would be checking the easy stuff first? KISS principle.... (Keep It Simple Stupid) I would be checking all that would/can affect compression, cams/cam timing/pushrods/rockers etc. All done without "opening up" the engine. Start easy, work up.......but then again I'm not into unnessessary extra work???
Copter

 

Agreed, not likely to be rings and pistons UNLESS it has some racing pistons with high compression. It ought to be a very strong runner; if the only problem is hard starting when hot, get the auto compression release (for each cylinder head).

 

There is nothing wrong with the rings or pistons. As everyone has said you will have low compression if there was a problem with them. Look into valve train for your problem. Don't touch the rings or pistons.

Your tech is not very good if he thinks to much compression is the problem.