Hi,

I own a 97 Road King and since some time ago it's getting more noisy than usual and some extrange noises makes me suspect that something in the valves isn't ok so I want to make a compression test and I have some doubts.

My first doubt is if is necessary that the compression test tool be expensive to get wright results or if any tool that I could buy in an autostore will do the job. I know that I have to look for a 14mm tool.

My second doubt is about what a compression test can detect. I've read that it can detect problems in valves and in the piston rings but I don't know if in a compression test can be detected any other problem that the bike could have.

Thank you very much. Ride safe and enjoy!!!

 

IMHO, no. Just be sure to use the "screw into the spark plug hole" kind, not the "hold the rubber thingy into the spark plug hole" kind, but it sounds like you already knew that.

Yes.

Only things compression related, which would include some but not all valve train problems.

Based on your description, I'd see if you can find someone local to you to give it a listen. Or maybe post a video here to see if one of the experts has a thought.

Cheers!

 

Thank you very much 0maha. I'm going to get the tool to do the test but first I'm going to get information about how to do the test in the better way and I'll post the results here.

I can try to make a video and post it here too, that is a good idea. In a first time I thought that it may be a lifters or pushrods question but I've disassemled them and they are OK so I think that it can be a cam bushing trouble or a valves trouble (maybe some bad spring).

The sound is like anything is not good inside the motor but it's very hard to listen where does the sound comes from, because I can hear everywhere. The worst is when the bike revs up where I can hear like a hammer knocking from the motor.

Thanks again.

 

Get a mechanics stethoscope or use a screwdriver to your ear. The stethoscope is great though, worth the price. you can pinpoint a noise very quickly. I had this weird sound I couldn't identify or find and someone guessed it correctly and recommended I get one. I bought it and within 30 seconds was able to confirm and locate exactly where it was coming from.

 

As for testing compression on one.

I like to start and warm up the motor a bit, pull the air cleaner to be able to hold the throttle plate wide open and pull the plugs. Either hole first and record results. 10% difference or less is ok between the two cylinder results. If seemingly low, add a teaspoon or so of oil and recheck each cylinder. If it goes up significantly, rings are not great and could be replaced.

Griz

 

Comp test should be done at full operating temp with the throttle wide open.

Bad valves don't make a noise, they just leak....bad noises from the valve area would usually be worn out rockers or rocker shafts, loose rocker assembly bolts or even the bottom end.

Low oil pressure or stuffed lifters would also be in the list of usual suspects.

A loose crank nut can sound like it's coming from the rocker gear too.

Comp test will tell you how the bike is ageing but most of what it tells you is not related to the noises.

Post the comp test results on here but I maintain 2 old Super Glides that have only 90psi and they run well, are mechanically quiet and use very little oil.

If the noises are getting worse over time then you need to think about putting some time and money into the bike. Post the mileage as it will give us a better idea of what the noises could be.

Kees had 100,000 miles on his RK and it sounded great but had shot rings and chunks missing from the valve seats.

If it was my bike I would do the comp test, if that is OK (comps within 5-10% of each other) I would (depending on mileage) check the crank nut, check the rocker gear and inspect the cam and lifters.

If all that was OK and I would think about pulling the jugs but unlike many of my American cousins I am an advocate of doing the minimum and not just hosing money at the problem.

 

How many miles on the beast?

 

Compression test tells you a few things. 1: you have compression 2: if thereally is a difference between your cylinders and 3: possibly worn rings. I prefer cylinder leakage test because you can find the source of the compression loss and attack it that way

 

You shouldn't have to spend a lot of money on a compression tester, I bought a craftsman many moons ago when I used to build car engines, came with three sizes one fits the evo. Don't know how much $ but not much.

 

I'll tell ya"ll something, a little back yard mechanicing if ya will.

Find the compression stroke on a cylinder, then put about 20 psi compressed air into the cylinder via the plug hole using an adapter for your air hose. Next use your ears....meaning, go listen at the end of your pipes, your intake and at the bottom of your crankcase. What you are listening for is air at these locations. If you hear air escaping at the breather you have an intake valve problem....hear air at the exhaust, you have an exhaust valve problem..and if you hear air at the bottom of the engine or the oil pan you have a ring problem....

$0.02