Compression Check on a 2 stroke

[DeanMember]

I have just done a compression check on my 3Hungey Gasser Throttle wide open and kick the bejeezus out of it 10 times. The average was 172psi I did it again with some oil down the spark plug hole and got 180psi.

My bike is setup with a .3mm base gasket,standard is .8 so compression should be higher than a bike with standard gasket. Is this a good reading?

The standard piston on the 07 Gasgas is a vertex, I have a new set of Wiseco rings for it,This shouldnt be an issue should it? The bike has done close to 5000 kays now,so maybe a complete top end is due? what are peoples thoughts?

Ollie

[drewMember]

not too sure ollie ol mate.

but i’d check piston to bore tolerances, inspect barrel to see how much it is out of round and for scuffing/ scoring etc.?

then work out what it needs from there.

[DeanMember]

yeh I might have to get me one of those bore gauges as I have to check the RMX dimensions as well.

Ollie

[murph the surfMember]

We used to use those bore gauges a lot at work
Would be perfect (as the name implies) for measuring cylinder dimensions
Cheers
Murph

[DavidMember]

Ollie I am not 100% sure but that does sound a little low for the thin gasket, how noisy was it,
I would be happy if it was 200-220
Where are you now, still at Kempsey

[DeanMember]

Ktmrat wrote:

Quote:

Ollie I am not 100% sure but that does sound a little low for the thin gasket, how noisy was it,
I would be happy if it was 200-220
Where are you now, still at Kempsey

No Rat back in Sydney

I thought 170 was not to bad :unsure: I will have to pull the topend off and have a Squizz. The bike didnt seem to noisy on the last ride. I have a new wiseco Piston kit here as well might have to put that in her.

Ollie

[DavidMember]

Mate stick with the vertex piston the teflon coating is worth HP, and longevity, also the wiseco are not controlled as well in their Manufacture, I have over the years had issues with the skirts breaking off as well as ring landings and both incidents end in catastrophic failure, thats why there is a price difference between wiseco and vertex

[DeanMember]

I already have the Piston Kit what about the Wiseco rings on the vertex piston if the piston is still within spec?

Ollie

[GlennMember]

Ollie wrote:

Quote:

I have just done a compression check on my 3Hungey Gasser Throttle wide open and kick the bejeezus out of it 10 times. The average was 172psi I did it again with some oil down the spark plug hole and got 180psi.

Ollie if you know what the manufactures specification is for the compression ratio here is a quick formula to convert PSI readings to engine combustion ratio.

Readings calculated at sea level 14.7psi
Using your figures as an example 172psi divided by 14.7 equals 11.7 therefore a ratio of 11.7:1 or 180psi divided by 14.7 equals 12.25:1

If the manufactures specification is 12.5:1 as an example the formula would be 12.5 x 14.7 = 183.75psi

[Bruce CurtisMember]

The compression formula isn’t as accurate on a smoker Mr 450, the primary and then secondary compression processes + the pipe effect tend to distort what should be.

Back to the burning Q at hand, I’m with Mr Rat, 170ish, if it is an accurate gauge cold indicates the lower end of “she’ll be right” zone for me, especially as you have tightened the dome clearance by using a thinner base gasket.
I have also had issues with Wiseco in the past, but I have been assurred by one and all that is in the past, still won’t use them though (once bitten and all that), I have also been caught out with different manufacturers rings and pistons, sometimes you never know until you try them together and check the clearance and fit.

Just another quick query, is the powervalve linkage on yours sloppy and has slack in it Ollie?

BC

[DeanMember]

Have to check Bruce, I have noticed that NP on DBW does a mod using heaven forbid KTM parts :unsure: which sounds like a good mod.

Definatley looking at least at the rings,Did you know Wiseco rings are made in Japan, I just read the package thought they were US

Ollie

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