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Discussion Starter #1
Just wondering what brand / style / adapter size are people using for a compression tester.

After so many threads/posts where certain person/s (yes Hubz, I'm looking at you!) have recommended a compression test as a starting basis for trouble shooting, I'm thinking it sounds like a fair enough idea.

So, what are the recommendations?

Don.
 

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Compression test is a waste of time. Imo.
A leak down test is only alittle more involved but tells you so much more.
A good leak down tstr will be alittle more money but not much.
Leak down tells you:
1.Bad/weak intake valves.
2.Bad/weak ex valves.
3.Rings.
Compression test you have to turn the engine over. You get one value.
If you deem it low, you still don't know why.

LD you make sure the cyl. is TDC, both int and ex valves are closed. ( valve cover needs to be off) someone is holding the crank.(ign rotor bolt) charge the cly with air through the plug. The LD will:
1. Tell you the % of air leaking.(0-20% good)
2. You will be able to hear the air leaking in the case(rings)
3. In the exhaust.(ex valves)
4. Frame (intake valves) (hav v-stack cover off)
You now hav a very good view of your internals as far as pistons and valves are concerned.

cmg
 

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Just wondering what brand / style / adapter size are people using for a compression tester.

After so many threads/posts where certain person/s (yes Hubz, I'm looking at you!) have recommended a compression test as a starting basis for trouble shooting, I'm thinking it sounds like a fair enough idea.

So, what are the recommendations?

Don.
Lets say both, Don. CMG has it right. A leak-down tester pinpoints. A compression tester gives the overall.

I use snap-on [brand] as a compression tester. They have all the plug adapters needed between engine sizes. I also have a hand held [blue-point], but our head holes are too deep, because they kept on closing the degrees of the valve angle almost straight up. So this makes the plug hole reach with a hand held a mute point. That's why you need a flex hose so it clears the frame: the hose is sitting horizontal more so the gauge can slide flat between head and frame.

With the leak tester, you need an air compressor for the blow down and follow cmg's list. With the compression tester, you can run dry first. Then, wet with ATF/any oil, so either the rings seal, you see a bump in compression, or it does not change, which means the valves leak.

Leak numbers run like this:

1-2% = New engine
6-7% = Race engine worn ~ Rebuild to be competitive back to 1% leak
9-10% = Production engine worn ~ Rebuild, she is clapped out

Compression numbers run like this:

We are looking at the same sort of proportion of the 10% leak. Say we check all 4 cylinders and they run... 200-200-180-200. The 180 psi is going to upset the idle sync for one. There is a 10% difference between the others = Tear down. You want an even wear pattern, right? Something got sucked in once, and it caused it to snowball. Look at the others still high in numbers, so something took a shit in the one chamber [there's a leak] somewhere?

You look in the book for this compression range. There is a wide range the bike will run in, but the cutoff is pretty high looking as well. I'm going to take the 14's book 149 ~ 228 psi. Look at how high the low number is for tear-down? I've seen some bikes 'run' at near 100 psi, but hard starting, idling and all that is the problem.

That 148 psi is saying this is your low performance number, we are done = Tear down, you went past the serviceable limit. The other is the 10% spread between cylinders.
Snap-on also has a self contained leak-down tester. All you need is a compressor, and if this plug is tiny like they use on the 14's, then it's a 10mm spark plug adapter.

Now, if you buy just a good quality 10mm adapter, you can alter the other end for a compression gauge. Because snappy time is big time money, you can see if motion pro has anything close?
 

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Discussion Starter #5
Thanks Hubz, good run down of how it works.

CMG, didn't think of a leak down tester, and also good info, still learning all about this kind of system checking.

Hagrid, I'm guessing 10mm?

Gives me something to think about. My bike is running fairly well, at the moment a bit rough / vibrations on acceleration and fuel economy not as good. I replaced plugs and cleaned / recharged K&N filters. Was thinking may be bad synch at moment; I have bought a Motion Pro Synch tool but it has the non-mercury fluid, and I have used it once (first time ever!). Problem was I noticed the fluid would get a small bubble in the top of one or two tubes when revving (even slowly), so not sure if mercury would have been better?

Nothing serious with the bike but as usual just making sure.

Don.
 

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YW, Don. The merc will bubble as well. The trick to that is to blow into the hose so the bubbles are out of the line, reattach, fire off, continue the sync.
 
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