compression test result - opinion needed

[Joce]

As some of you know, I'm looking to buy a kawa zl900 nearby.

The bike has been sitting for the last 2 years without starting.

The carbs need a good clean up mainly the #4 that dont seem to run.

Done a compression test last tonight. Cold motor, all plug out and open throtle.

Result are #1: 160 #2:165 #3:120 #4:150

Put oil in #3 and went up to 175.

Would it be possible that that this is a stuck ring on#3?

I know i would have better number with a hot engine but wasnt set up to have it run for long enough.

Thanks for your opinion.

[WillyD]

A jump in the compression like that with oil, would indicate rings worn in that cylinder...Being that the bike sat for a while I would say those numbers are all pretty good....With a warm engine, you would probably get a better all around compression reading...

Willy

[Blagadán]

I cant take the credit for the following info, I cut n pasted it from another website some time back and saved it to a folder for future use...

Interesting info on determining the results of a comp test...

"A good compression test result will show a quick build up of pressure, around 66% by the second revolution, 80% pressure on the fourth revolution and maximum pressure on the sixth revolution, with no more than a 10% variance across all cylinder (some prefer to use 1 Bar (15 psi) for the variance figure). The higher the figures, providing they don’t exceed the maximum pressure figure, and the lower the variance across all cylinders the better. If that’s the case all’s well, re-fit the spark plugs, connect the HT leads, ignition module plug or LT lead and re-fit the fuel pump fuse and your done.

An acceptable borderline compression test result will show a slow build up of pressure, less than 66% pressure on the second revolution and/or less than 80% pressure on the fourth and sixth revolutions, and 80% or more by the tenth revolution, with no more than a 10% variance across all cylinders. This is a sign of piston ring/cylinder bore wear or camshaft lobe wear, a wet compression test will confirm which – see below. Providing there is no tapping, chattering or knocking from the cylinder head/block and that the engine normally runs smoothly there’s probably not too much to worry about. Do another test next time you change the spark plugs, or if the engine starts running rough or losing power.

If any cylinder shows more than the maximum pressure suspect a build up of carbon in the combustion chamber, head removal and de-carbonising may be required. If ignored excessive pressure could lead to a blown head gasket or a cracked cylinder head, check the spark plug condition before deciding if the cylinder head needs to come off. Note on a good engine you could see as much as maximum pressure +20% by the tenth revolution this is due to the non-return valve on the tester preventing the pressure from dropping within the gauge.

If adjacent cylinders show low pressure (greater than a 10% variance) this could be due to an internally cracked cylinder head or an internally blown head gasket between those cylinders. This can be confirmed by the presence of coolant in the oil and will be recognised by a whitish colouring to the engine oil (check the dip stick) and a build up of suds (a whitish oil and water mix, sometimes referred to as froth or mayo) inside the oil filler cap.

If any cylinder shows less than 80% maximum pressure a major engine overhaul is on the way, but don’t panic too soon, many engines have been known to run fairly well with 70% or less pressure, just don’t race them. Carry out a wet compression test.

Wet compression test

A wet compression is carried out the same way as a normal test except that you pour 5ml of engine oil down each spark plug hole just prior to fitting the compression tester, allow about 30 seconds or so for the oil to settle around the piston rings and form a seal. Don’t forget to write down all three or four pressure readings for each cylinder. Compare the wet compression test results with the first set of test results.

An increase in pressure indicates worn piston rings and/or worn cylinder bores, as the additional oil has acted as a seal.

No increase in pressure points towards the camshaft or the valve gear and could mean any combination of: pitted or worn valve/valve seat, bent valve, worn valve guide, burnt valve or a worn camshaft lobe.

No increase in pressure may also be due to an externally cracked cylinder head or externally blown head gasket this would be a little obvious though, as you should be able to hear it hissing/popping or see it bubbling.

When your done re-fit the spark plugs, connect the HT leads, ignition module plug or LT lead and re-fit the fuel pump fuse."

Blag

[texas-ss-tornado]

If it's been sitting for a while, I wouldn't trust the readings at all. True story. Bought a Bandit 1200 on Craigslist a few months ago, was basically lied to and was told the bike was fresh out of a dry storage. Truth was, it was fresh out of a flood of some sort, 3 out of 4 cylinders were FULL of water, it was a mess. The first compression test I did showed 0, that's right 0 pressure on 3 of the 4 cylinders!!!!! I was told to give it up, bike would never run again. But I persisted! There must have been rust or something on the valves keeping them from closing, but believe it or not, I dried the thing out with my air compressor and got it to start eventually, and after it blew all the water out, (water shot 12 feet out of the exhaust), the compression results were 150, 160, 140, 145........and it runs like a top! I wouldn't trust any results until the bike has been restarted and ran for awhile, that's all I'm saying...........

[lowlife]

Agree with everything said above. Motor has got to be warm to be accurate ....however I also agree that for what you had to work with the measurements are tolerable, but #3 suspect. Did you add oil to the other cylinders? Was the throttle open on all? You are looking for a variation, not necessarily the number itself as gauges can vary.....quit a lot.... What did #3 plug loook like. Any different than the other 3? Did you pump the cylinder that same revolutions on all 4 cylinders as Blags article said. BTW good article blag... How many miles on the clock?

My recommendations are to go back and try it again if there is any doubt following all guidelines given. Warm is always better as we want the cylinder round when warm and really don't give a crap what shape they are while cold. If all you have to work with is cold.......then I would just realize I may have a weak cylinder....possibly....also seen engines come "out of it' with a slow wake up from their 2 year nap. Personally I would use it as a bargaining chip and not let it scare me away depending on price.

[paulfun]

I would simply buy it and run it!
Bet after a few days of normal rideing the compression test comes out way better!

[lowlife]

I would simply buy it and run it!
Bet after a few days of normal rideing the compression test comes out way better!
Hmmm took me 3 paragraphs to say what you did in one........... :pottytrain1:

[Joce]

Thanks for your comments.

I'm gonna take a chance on the bike. It's'comming home this week end.

The bike have 42000m and the price is 1500$.

Second owner and he was doing good maintenance on the bike. Just did'nt had time to run it last summer.

I'll start with a good clean up, replacing all fluids, probably try something in the cylinder to free the ring if its the problem (heard of pb blaster). Have the carbs rebuilt (by one of the member here providing that service) and then how is the mecanic.

Hope it will be ready for may.

Joce