How determine the factory spec (off the production line) compression?

[edelweiss]

I have a Yamaha DT360 (2-stroke) Enduro. How do I determine what the factory spec compression should be?

Here are the specs:
Engine Capacity: 351
Bore x Stroke: 80 х 70 mm
Compression Ratio: 6.4:1

Thanks!
John

 

[barnett468]

I have a Yamaha DT360 (2-stroke) Enduro. How do I determine what the factory spec compression should be?

Here are the specs:
Engine Capacity: 351
Bore x Stroke: 80 х 70 mm
Compression Ratio: 6.4:1

Thanks!
John

OK I'm guessing that you want to know what the psi should be using a gauge . . this info will be in the service manual but 6.4 static sounds like a typo to . . 8.4 sounds far more realistic to me . . either way, if the static compression is less than around 140 psi, something is wrong . .

 

[edelweiss]

OK I'm guessing that you want to know what the psi should be using a gauge . . this info will be in the service manual but 6.4 static sounds like a typo to . . 8.4 sounds far more realistic to me . . either way, if the static compression is less than around 140 psi, something is wrong . .

Thanks barnett. That is actually the compression ratio (no typo). I found some info, yet to be verified, where a person said the optimum compression should be between 150-170 psi. I will measure my piston's OD to get the right rings. Because my compression is only 120 psi right now. :-[

 

[barnett468]

No prob.

You need yo have the cyl measured . . if it is out of round or tapered by around .002", I would bore it . . measure the piston for wear . . if the piston to cyl clearance is more than around .0045" I would bore it

A cheap gauge can be off by up to 20 psi.

170 is about all you want for premium gas.

it

 

[mydlyfkryzis]

2 strokes have crankcase compression, kind of like having a supercharger....So the cylinder compression seems lower than a 4 stroke, the total compression of the charge ends up around the same PSI.

Honda CB360 uses regular gar (86 PON) with design 170 PSI compression.