engine compression

[BlueRex]

ok following on from my introduction viewtopic.php?f=12&t=18579

the figures i received from the mechanic were as follows
Motor very tired 75-85% leak down
Ht comp test #1 122 #2 90 #3 95 #4 120

who knows a reputable mechanic who can confirm or call bullshit on these figures in the western suburbs or city. roughly how much would it cost to test this as the bike only cost me 2k so don't want to start spending huge amounts of money on it.

Thnks
Scott

[mike-s]

You can do it yourself, get a generic compression tester from supercheap for $20 or so and you can check the figures and you now have a comp tester to use at a whim. Or someone else here with one could do it for you if they have one (or even help you use yours if your not that confident on doing the test yourself).

If you were in sydney i'd offer my help as i bought that very tester to check out my project bikes compression stats.

[ozten]

Its dead easy to do yourself, after you check all your cylinders out put some oil in there then check them again, if the compression goes up your rings are farked

[Slow and wobbly]

Its dead easy to do yourself, after you check all your cylinders out put some oil in there then check them again, if the compression goes up your rings are farked

But I doubt from the kilometers traveled this would be the case. Probably more like lack of valve clearance which can be easily resolved. But it's only a guess. If your interested you can drop by here and I would be happy to look at it for you.

[ozten]

Its dead easy to do yourself, after you check all your cylinders out put some oil in there then check them again, if the compression goes up your rings are farked

But I doubt from the kilometers traveled this would be the case. Probably more like lack of valve clearance which can be easily resolved. But it's only a guess. If your interested you can drop by here and I would be happy to look at it for you.

Lack of valve clearance will have no effect on compression, and that is why you do a leak down compression test, to rule out the rings which would be the most likely suspect

[Rossi]

What S & W meant was poorly lapped valve seatings or an excessive carbon build up on the exhaust valves.
Did the mech do this before or after the "full" service ( which should have included
re-shimming the valves) ??

I seem to remember another member being told he had poor compression from the same place a while ago and it's still running good
Do you intend racing this bike in top flight competition ?
If not ride it and enjoy

[Slow and wobbly]

Its dead easy to do yourself, after you check all your cylinders out put some oil in there then check them again, if the compression goes up your rings are farked

But I doubt from the kilometers traveled this would be the case. Probably more like lack of valve clearance which can be easily resolved. But it's only a guess. If your interested you can drop by here and I would be happy to look at it for you.

Lack of valve clearance will have no effect on compression, and that is why you do a leak down compression test, to rule out the rings which would be the most likely suspect

But if there the clearance has closed right up then the valve or valves will remain open and show low compression when performing a compression test. Yes the oil test will indicate ring wear but you have only provided the one outcome;

if the compression goes up your rings are farked

But what if does not? Then this would point to valve clearance issues yes?
To perform a Leak down test more than a compression tester is required. Each cylinder needs to be tested by pressurising it at TDC with valves closed using compressed air and an appropriate leak down tester.

[Rossi]

Each cylinder needs to be tested by pressurising it at TDC with valves closed using compressed air and an appropriate leak down tester.

Sounds like summat me and you could knock together in half an hour if needed

[Slow and wobbly]

Oh and to be sure I was right I googled your comment
"Lack of valve clearance will have no effect on compression" to see how many others agreed with you
And came back with this from here - http://en.wikipedia.org/wiki/Four-stroke_cycle" target="_blank" target="_blank
"Lack of valve clearance will prevent valve closure causing leakage and valve damage."


I'm right nah nah nah

[Slow and wobbly]

When you say - back in the other post - it was in for a full service was this major or minor?
Big difference. Did they actually check the clearances?

[ozten]

To perform a Leak down test more than a compression tester is required. Each cylinder needs to be tested by pressurising it at TDC with valves closed using compressed air and an appropriate leak down tester.

Jeez im just talkin bout the backyard method of going about things which works quite fine, lets not get too technical its not a race bike.
One more thing shims wear out they dont grow so no your valves will not remain open

[ozten]

My bad, dam me and my skim reading, its pretty unlikely that the valve clearances were set incorrectly, you have to be a fair numpty

[Slow and wobbly]

To perform a Leak down test more than a compression tester is required. Each cylinder needs to be tested by pressurising it at TDC with valves closed using compressed air and an appropriate leak down tester.

Jeez im just talkin bout the backyard method of going about things which works quite fine, lets not get too technical its not a race bike.
One more thing shims wear out they dont grow so no your valves will not remain open

No but valves stretch and seats become recessed which is why the valve clearances need to be checked periodicaly. When this happens the gap between the cam lobe and the bucket closes up and can cause the valve to remain open. To re-open the gap a smaller shim than what is already fitted is required. Shims don't wear out as they are nothing more than a spacer between the valve stem and the bucket, hence the name shim.

[BlueRex]

When you say - back in the other post - it was in for a full service was this major or minor?
Big difference. Did they actually check the clearances?

It was checked in for a major service but when they called to tell me it had half the compression it should and would cost ball park figure of 2k to fix i said forget it for the moment i am not prepared to spend that much at this stage.

When i got the bill they said they did half way between a minor and major service this included.

replace spark plugs
oil filter
oil
valve clearance
HT comp test

[mike-s]

and just how much did that cost you?


btw, leakdown test, might have to look into doing that on my 250,then again ive not even done a comptest on my 900, might do it once i cbftaking the tank off, which requires taking the top of the ducktail off