Rod side clearance question

[Bailey28]

Hey guys, I am in the middle of doing the base gasket mod on my '10 300.. I have about 75 hours total on the bike from brand new..

The stock squish if anyone is interested is 2.55mm with two green .030" base gaskets as delivered. Cranking compression full throttle was 130psi after about 10 kicks.

Anyway, onto the question at hand: I measured just the rod side clearance and it is at .040" (inches, not mm)... I thought they were supposed to be tighter than that but I could not find anything after doing a search.

Both piston rings are at .015" gap near the top of the bore squared up.

Any light that can be shed would be great, so I can maybe stop freaking out here. Thanks !

[stainlesscycle]

that squish is obnoxious. get rid of 1 of those .030 gaskets. will put you at 1.788mm - i run mine much tighter than that at 1.2mm (1 .015 gasket)... but you gotta up octane or it'll ping. and maybe retard timing a degree. but 1.78mm squish should be perfectly fine with stock timing, 93 gas. you will feel the difference.



your side clearance at .040" is not terrible (that's total - you pushed the rod to one side right?). spec is between .030" and .040" if it's any consolation. old air cooled 2t's have even looser specs...

as long as there's no vertical play, it's probably fine.


bore justifies ring gap, but i would assume spec to be around .4mm - .5mm - push the rings down to just above the exhaust port, and remeasure...make sure they're square. you're not seeing any wear on bore i would assume - right?

[Bailey28]

Just came back in from the garage,, and....

No bore wear, really no piston scuffing or wear. Most of the black coating is still on it. The piston top was really clean, with a small heart shaped carbon mark on it.

Rings are still .015 farther down in the bore. The rod was pushed to one side, .040" max will fit in there. No up and down movement. No crank bearing movement. I keep the filter clean, and at best I am a B rider, and love to lug the bike.

Cylinder says "A" on the rear, piston says Vertex, 71.93mm. I took out the powervalve and skateboard bearings to clean them as well.

On squish, I have one new teal green gasket that is .010" as measured, and three brown paper bag type that are very thin, .007" or so.

With only the one green gasket and minimal torque on the cylinder base and head, squish is still not great. I can just get the edges of the solder to start smashing down. The solder is .092".. Squish right now with the single .010" gasket is about .090", or 2.2mm. I did not fully torque the cylinder base, I did maybe 10 ft/lbs by hand. I torqued the head to 10 ft/lbs. also.

This motor must have been closer to 3mm squish,, unless I am measuring things wrong... Just for number sake, I measured the head step at .095". At max TDC, I measured the piston 0.161 down in the bore at the wall edge.

By this measurement, I should have .066" at the very outer edge between the piston and head. But running the solder, I get .090".. I am turning the flywheel by hand following ron's instructions.

[stainlesscycle]

Originally Posted by Bailey28

This motor must have been closer to 3mm squish,, unless I am measuring things wrong... Just for number sake, I measured the head step at .095". At max TDC, I measured the piston 0.161 down in the bore at the wall edge.

By this measurement, I should have .066" at the very outer edge between the piston and head. But running the solder, I get .090".. I am turning the flywheel by hand following ron's instructions.

by those measurements you should get .066", which is 1.67mm - a decent number, but that's without a gasket right? because by that data, it would be impossible to get any tighter squish without machining.

i found an error in my last post - and in yours i believe - i used .15mm gasket, not .015". (the thinnest one available..) and the gaskets are available .5mm, .3mm, and .15mm, not inches.

so the gaskets you started with are .3mm not .030" - maybe you should go back and do everything in mm so there is no confusion... i did my math based on your original 2 .030" gaskets - which is wrong.

[Bailey28]

I realized I was screwing up last night after looking at the old gaskets again... The old ones are two of the same light green gaskets which measure .038" (two .5mm gaskets at .019" each).

I don't have a metric micrometer so I have to convert back and forth to inches.

With the new gasket in place, a teal green that is a .011" (.3mm), I can get the piston to within .161" of the top of the cylinder deck. So ultimately, I only lowered the cylinder by .027" or .68mm. Not much change over the stock set up.

I will head back out this morning and try some playdoh as the Solder was really not touched even with the new gasket in there.

I had the solder over the centerline/pin of the piston so piston rock would be less apt to affect the measurement here.

I'll try to convert more accurately back and forth, what a pita... but thanks for your input Stainless!!

[stainlesscycle]

Originally Posted by Bailey28

With the new gasket in place, a teal green that is a .011" (.3mm), I can get the piston to within .161" of the top of the cylinder deck. So ultimately, I only lowered the cylinder by .027" or .68mm. Not much change over the stock set up.

.68mm is more of a change than you think. 2.55mm squish versus 1.87mm. when you get in the 1.6-1.8 range it's starting to get efficient. the thinnest .15mm gasket will get you 1.72mm which is better than what many are unknowingly running.....

[stainlesscycle]

if you look here

http://www.gasgasrider.org/forum/showthread.php?t=10113

you'll see that 2.5mm to 1.8mm gave almost 3hp (*theoretical) all over.. but if you go too far, without raising the exhaust port back up, you lose topend. for me that's almost a non-issue. very hard to utilize 50hp in the woods.


if you're sending the head to ron, i would think the .3mm base is what i would use to measure with, that way you don't alter port timing too much, and he can cut squish down to 1.2 or whatever he cuts to.

[stainlesscycle]

hope you get it figured out - i'm packing for gncc, so can't concentrate on figuring the numbers. someone here will give you a better recommendation maybe?

[Bailey28]

Thanks! I wish I was going to a GNCC... I got it figured, it is .066" (1.67mm) at max TDC, with the .3mm single teal green gasket. I torqued everything down this time and it was much more consistent. I will do a compression check after I get it together and post the difference. 130psi was stock.

I don't need 50hp either and never really ride high up top. I need the bottom end for sandy woods and sandy moto.

[bchatt]

I have found that if you use the brown paper gasket (.15mm) you need to use gasket sealer of some kind, other wise it "weeps". The green gaskets (.3mm) seem fine without.