650sx compression

[cosworthspeed10]

Hi,
Just done a compression test on my 650sx this afternoon. 125 and 135psi were the readings. Is this pressure acceptable for a stock ski or not? I have just done a rebuild on the ski to clean the engine and powder coat it. I put a new gasket set and crank seals on the engine. The bore's looked like new so I didn't put new rings on.

Is it possible to machine the stock head and if so how much do i need to take off to increase compression to arround 165-70psi?

Thanks Guys, sorry for all questions!

[ScatteredFormat]

Re: 650sx compression

costworth, my stock 650 was running 130 both holes, i sent the head out the get milled .020 and am getting it back today, if you want ill post my data

[cosworthspeed10]

Re: 650sx compression

Yes, please report the results!

[u887266]

Re: 650sx compression

If it was me and I might be wrong, but if you rering the engine I would run the engine first to let the rings get set in and also let the engine heat up, then take the compression check. More then likely you will get a different reading.

[cosworthspeed10]

Re: 650sx compression

I Didn't put new rings in, so they should already be bed in. I have checked the compression also while the engine is hot!

[ScatteredFormat]

Re: 650sx compression

well, head is on, but i just happen to loose the tourque wrench adapter so i think they are around 14 or 15ft lbs right now and the psi is dissapointingly the same

[cosworthspeed10]

Re: 650sx compression

That don't make sense! You have reduced the volume so compression must be higher?

[ScatteredFormat]

Re: 650sx compression

i know! idk what the deal is.. i picked up the head..ran down and picked up a gasket......bolted it down to about 14ftlbs and it was 130.. i highly doubt tourquing it down the 22ftlbs is going to change the psi at all..

[ljbarryiv]

Re: 650sx compression

I put new pistons in and honed the cylinders in my stock ski with standerd bore 87 650sx. Before brake in it was 145psi in each. I think 130 is a little low. You may want to rebuild. I haven't checked it yet but I bet its close to 150 now.

[64coupe]

Re: 650sx compression

i know! idk what the deal is.. i picked up the head..ran down and picked up a gasket......bolted it down to about 14ftlbs and it was 130.. i highly doubt tourquing it down the 22ftlbs is going to change the psi at all..

What was the head gasket you picked up? Did you have an after market one on there before the milling that was thinner? Just a thought?

[ScatteredFormat]

Re: 650sx compression

i had a stock one on before the mil, and i bought a stock one for after the mil

[perryak]

Re: 650sx compression

I put new pistons in and honed the cylinders in my stock ski with standerd bore 87 650sx. Before brake in it was 145psi in each. I think 130 is a little low. You may want to rebuild. I haven't checked it yet but I bet its close to 150 now.

Sounds a bit low to me too. I recently put a high compression head on my 650sx. Before i put it on the motor was totally stock, and compression was 165 per hole. I replaced with the same size gasket, now its 200 psi per hole. I admit I have a cheapo compression tester and the numbers might not be spot on, but they should be close.

[ljbarryiv]

Re: 650sx compression

Sounds a bit low to me too. I recently put a high compression head on my 650sx. Before i put it on the motor was totally stock, and compression was 165 per hole. I replaced with the same size gasket, now its 200 psi per hole. I admit I have a cheapo compression tester and the numbers might not be spot on, but they should be close.

The 87 I have was totaly stock with stock head at 145psi. I have a 91 that I rebuilt as well which has a stock milled head thats at 180psi. 130psi is really low for a stock 650. I would rebuild the top end I think when they where new they were like 160psi.

[ScatteredFormat]

Re: 650sx compression

so i finished putting everything together today, and i charged the battery.....(mistake much?) and i got 150 per hole. so started with 130, mil .020 result 150.
so, a .020 mil will give you 20psi, so i guess you could assume .010 would give 10psi and so fourth...

[cosworthspeed10]

Re: 650sx compression

What do people suggest then, New rings and hone or pistons too?