GS1000ET, compression test, new gasket!?

[cleiper]

Hi folks,

When I first stripped down my motor a couple of years ago I noted that the bike had the original Suzuki GS head gasket, with the black oil pathway seals fitted in the 4 outer mounting stud holes.
The first time I rebuilt it I used a cheapo gasket, which later leaked oil, but before it failed the leak down and compression test results were very good/high.

Since then I decided to go to Suzuki for the next head gasket and they said the originals were no longer available, but had been superseded by a 3 layer metal gasket affair. 11141-49410 GASKET Note: this part is superseded by 1114149410.

After re-assy with the new gasket I did a leak down test which showed good results, but the compression test is now down in the 80-90 psi range.
Have any of you folks fitted this newer style Suzuki gasket and found the same issue?
What are your PSI readings for comp test?

Cheers!

[salty_monk]

Checked the valves recently? Made sure the camchain is on right?

It surely can't be so much thicker it affects compression that much...

Are you testing compression hot With throttle wide openin both cases? If 2nd test is cold and first hot that would explain it.

[cleiper]

Thanks for the reply,

The leak down test failed to show any issues with the valve's seal or any other leaking, no noises heard from carb, exhaust, oil filler or between cylinders.
Although I don't remember if the original compression test was hot or cold, the latest one was done cold. It was done with throttle wide open. Do you think I coud get an extra 30 PSI just due to engine temp?

Anyone else fitted this new layered metal type gasket to their GS?

Cheers.

[Nessism]

I don't know exactly how much compression will increase with a hot engine but I know it will. And those MLS head gaskets are good so no worry there.

[hampshirehog]

You might get a compression increase with a hot engine - you usually do but not always (no idea why / why not - just happens).

And yes a thicker head gasket can knock quite a bit off your compression figures, even if it's only slightly thicker. In the same way, valve reseating can lower the numbers. The reason is that the combustion chamber is a pretty low volume (I did know the rough figures at some time for several bikes but I can't remember them now) and making that small volume only slightly bigger with a thicker gasket or with the valves slightly more recessed can make a big difference relative to the original.

Having said that, 30psi does seem a lot to lose. Someone on here will know the combustion chamber volumes and be able to help you do the maths.

[chef1366]

If you have not had the motor machined then the compression should be stock with a stock gasket.
Did you replace the rings?

[Big Jay]

Did you do a leakdown test with a real tester that shows precentage of leakage? If so, what was the leak number?

[cleiper]

Thanks for the answers.

The barrels were honed and new rings fitted and valves re-ground in on the first rebuild.
If these had been an issue the leak test should have showed it up.
My leak tester does show percentage of leak but all I remember is the 4 quadrants of the gauge, red-very bad, orange-Bad, Yellow-poor and green-good to excellent.
All cylinders were somewhere in the green range.
I am almost certain that the new metal gaskets are thicker, but since the old one is long gone I can't be sure.

All shims and valve timing are by the book, so I can only guess that If I want to get the numbers up I will have to have the head skimmed to compensate for the (Possibly) thicker gasket.

What are your guess's as to the difference in running with 90PSI comp as opposed to 110-120PSI. Much??

Cheers

[Nessism]

The gasket is NOT the reason for the low compression; I very seriously doubt the thickness difference of the two OE gaskets, as installed and torqued on the engine, is significantly different from each other. If the engine work was performed properly last time you shouldn't have anything to worry about. Ride the crap out of the bike for a few hundred miles and then recheck the compression, this time with a hot engine and throttle wide open, and then judge. Needless to say the valves need should always be checked after a rebuild, and make sure you retorque the cylinder head a couple of different times within the first several hundred miles to make sure everything is snug.

[tkent02]

Ride the crap out of the bike for a few hundred miles and then recheck the compression, this time with a hot engine and throttle wide open, and then judge.

+1, ride it hard!