was traveling on the highway running ~70 when the bike started slowing then just shut completely off so i coasted to the side of the road and start to restart her. bike was cranking but not firing. had just filled up not even a mile away. bike was getting fuel so i pulled the plugs to check them out as i just replaced them about 1k miles ago. reinstalled then and tried to restart. bike started but was only a sputter for a brief moment then it shut off. it would not restart. while cranking there was an odd sound from the rear cylinder as it didnt sound like the front. pulled the plugs and put my thumb over the front cylinder spark plug hole while cranking and the compression almost blew my thumb off. tried the same with the rear and i barely felt and pressure. i was about 200 miles from home and was with a few other riders and a truck with a trailer so I trailered the bike home. just pulled both cylinders but do not see what the issue is. I was going to go 107 kit this winter so looks like I will do this now. however, I have no idea what went wrong and would like to know before I put it back together. cylinders look great...pistons have carbon buildup but I don't think that would cause a loss of compression. could there be a hole in the piston under the carbon. what are some of the reasons for loss of cylinder compression.
bike is 2012 flhx with 18k.
any ideas what I should be looking for at this stage.
thanks

 

Need more information. What was the last modification made? Have you checked the heads? What pushrods are you running? How do the rings look?

 

last modifications were cams about 4k miles ago. adjustable pushrods. don't see a difference in the heads but I don't have a trained eye. what should I be looking for. I can take pics of any part you need to see. rings look good on both pistons. I cleaned the carbon off the pistons but the combustion chambers are caked a little also .
thanks

 

uhoh...looks like i jumped the gun..just checked the lock nut on the intake pushrod on that cylinder and its loose and has moved up the threads..damn..that would cause the loss of compression on that cylinder won't it. damn..should have posted first.

 

That is where I was headed with the pushrods; loose jam nut.

 

Gotta love adjustable push rods. Tried them once, pita, last three bikes pulled the rockers instead. Less trouble when all was said and done but that's just me.

 

I gather its all good to reinstall everything with new gaskets and button her up or no.
thinking about having the cylinders bored, heads and throttle body ported and possibly changing cams to match since im this far.
thoughts?

 

Glad you found the problem. When you button her back up, add a External Breather System to your A/C, or get and A/C that already has an EBS, that way you won't get all the performance robbing hot, oily, oxygen depleted air into your combustion chambers, which is also causing that carbon build-up you saw.

LINK to info on EBS's.

LINK to Performance A/C's.

Feel free to come down and visit us...we're just down the 78 from you.

 

Yup, put her back together, no worries. Might consider a dab of red thread locker on the jam nut. I don't put it on the threads but use a toothpick to put a drop between the jam nut and pushrod base just before tightening; haven't had one come loose since I started that practice.

If you have the wants and funds, why not bore to 107? Machine work, new pistons and most importantly, head work is really all you need. The 222 cams should respond well to the compression increase but if you want more lift, there are many cam options and Cyclerama has some good ones in their lineup. No need to bore the T/B unless you just want to. Replace the FP3 with the Power Vision, dyno tune and done. See how the exhaust responds to the upgrade; you can always change pipes.