what psi should our engines be
- Thread starter brianfulcher15
- Start date
Most say 120-110 is good. For a stock engine. Below 110 you might be looking to do a top end rebuild. Just repeating what I've heard mentioned several times here.
It depends on the builder and parts used.
The STOCK spec blaster engines I build have aprox 130 psi after break in. Other builders with looser specs might be around 120 psi
I personally dont recommend running below 115 psi,
It will save you from breaking pistons, also you engine is getting pretty weak running lower then 115 psi... I have never seen a Blaster with 100-110 psi with the ring end gap within decent specs.
Its cheap and simple to re-fresh the top end so there is no reason to run it on low compression.
The STOCK spec blaster engines I build have aprox 130 psi after break in. Other builders with looser specs might be around 120 psi
I personally dont recommend running below 115 psi,
It will save you from breaking pistons, also you engine is getting pretty weak running lower then 115 psi... I have never seen a Blaster with 100-110 psi with the ring end gap within decent specs.
Its cheap and simple to re-fresh the top end so there is no reason to run it on low compression.
My Clymer manual lists it at 140psi.....however I've generally heard 120psi, so somewhere between.
Yep
The clymer manual was writen back in the early 90's using the old style paper gaskets. the were thinner and compression was slightly higher. i remember building engines that were that high. Todays OE gaskets are slightly thicker and better but the down side is... the compression is slightly lower.
as I said in another post the math shows a UCCR of 135 psi. But real world compression anything above 130 is good. 120 is ok, below 115 and it needs attention asap.
The big problem is not body tests the compression before, during and after break in to get a base compression to monitor the engines state of tune. Sadly people that have rebuilt engine that have 120 psi after break in either did not break it in properly fast enough or the specs are on the loose site.
The clymer manual was writen back in the early 90's using the old style paper gaskets. the were thinner and compression was slightly higher. i remember building engines that were that high. Todays OE gaskets are slightly thicker and better but the down side is... the compression is slightly lower.
as I said in another post the math shows a UCCR of 135 psi. But real world compression anything above 130 is good. 120 is ok, below 115 and it needs attention asap.
The big problem is not body tests the compression before, during and after break in to get a base compression to monitor the engines state of tune. Sadly people that have rebuilt engine that have 120 psi after break in either did not break it in properly fast enough or the specs are on the loose site.
yfs101 was refering to base gasket. Head gasket is copper. Do belive there are thinner hi comp availeable, know nothing about them as to increase or quality.
yeah the base gaskets used to be thin paper this a tiny bead of sealant. They changed them in 02 to a thicker fiber base gaskets (coated) for a much better seal.
As far as I know the head gaskets are the same from Yamaha. Thinner ones are available as well but must be used with a copper spray like any metal head gasket should.
As far as I know the head gaskets are the same from Yamaha. Thinner ones are available as well but must be used with a copper spray like any metal head gasket should.
I think I just put a Cometic on mine when I did the top end 7 years ago....can't remember. And touche on the copper spray....always use that.
130-140 for a stock fresh (seated rings) motor. Anything over 180 and the squirrels start fighting each other.
perfect.
now check it every couple months, when you see it getting down around 115, freshin the top enbd up.
now check it every couple months, when you see it getting down around 115, freshin the top enbd up.
Yeah my quad is at 90psi and it needs a top end i guess, I would have never known if i wouldnt have checked it with the compression tester, now i just hope i dont mess up the rebuild.....lol
Yeah just be sure to use good gaskets, and when installing piston pin clips the gap is always facing up or down, never to the side.
Always do a leak down test before you run it... most top end leaks are around the reed block and manifold, a light coat of threebond 1211 will keep it from leaking.
Always double check the caped off oil port on the carb is plugged up if you are running the injection blocked of.
Always do a leak down test before you run it... most top end leaks are around the reed block and manifold, a light coat of threebond 1211 will keep it from leaking.
Always double check the caped off oil port on the carb is plugged up if you are running the injection blocked of.
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