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anybody have pro or con opinion on using 2 base gaskets ?

Are they about ten thou thick? Methinks it wouldn't be enough to make a noticeable change in port timing. Without doing the math, It could make a bit of a noticable change in compression.
I have played with shimming jugs and stacking base gaskets for port timing changes and to play with compression. Not ideal, but good for R&D. It seems that it took about twenty thou to get any noticable expected change.

.02

thnx for the input. i was thinking of putting my degree wheel on there with 2 base gaskets and see what happens

Dude are you ever gonna quit grinding on shit?

britincali wrote:Dude are you ever gonna quit grinding on shit?

hey bitch i got new tools and they dont like collecting dust

britincali wrote:Dude are you ever gonna quit grinding on shit?

TYSTYX wrote:

britincali wrote:Dude are you ever gonna quit grinding on shit?

If you would ride as much as you tinkered with shit you would be a Pro rider by now.

Tough crowd.

does the piston go below the port now?

Just for the record Maico used to offer 3 diffent base gasket thicknesses that allowed fine tune of desired powerband character. Ranged from thin for more bark down low to thick for more over-rev. It was noticeable. Particularly if you made fuel, pipe and or timing changes to compliment base gasket selection.


GenIII AF500
91 CR500
84 CR500
06 YZ450
74 Rickman 250
4 81 490 Maicos
& more....

Roostius_Maximus wrote:does the piston go below the port now?

no. how would the piston get below the port ?

I remember seeing a snap shot of Bailey's bike in MXA in the '80s. I forget the year and the race, but they showed a stack of gaskets under his cylinder.
Supposedly to cut down on wheel spin to create more drive.
Never did give the results though.

Less wheel spin from a 500....is that even possible? I remember when they banned paddle tires, maybe bigger knobbies would have helped.

theres a reason why someone would use 2 base gaskets, but the people who have the answers werent answering their phones today . you wouldnt think 1 extra gasket would make any difference but maybe it does. im wondering how much the thickness of the 2nd gasket will change port timing ?

100hp honda wrote:

Roostius_Maximus wrote:does the piston go below the port now?

no. how would the piston get below the port ?

If the jug is raised enough the top edge of the piston will travel below the floor of the exhaust port... nothing a grinder couldnt fix though

This used to be popular cheap fix on 490s as a bandaid for there fucked up like a football bat squish bands. It will change port timing a lil, but the big diffrence is the lowered compression and larger squish area, creating some unfavorable flame pattern in the combustion chamber if your not careful. You'll probably see a lil more over rev and a lil less bark down low if you double gaskets, any more than that and your gonna have to start tuning for it to optimize it. Chaniging timing, port work to correct the port timing change, pipe and ignition tuning, rejet. Its a good power tool, but only inconjunction with a ton of other shit.

if the port floor is stock now and you grind it lower to match the piston now, its maybe .015-.020 different, but that = exhaust port timing thats earlier. I like the big hit so my stuf has the piston as close to the floor of the port as possible,and make the intake ports taller 1mm. i've even milled the base of the jug .008 to drop it down and get the piston proud of the jugs deck. Then its holding the cyl pressure longer down the hole, more power, and the port work needs to be done properly to blow that last bit out the pipe harder than original.
I'm working on a set of 86 cases at the moment, it'll be easy to check the power on it using a 87+ crank, but changing the deck height with different spacers to see whats best.
if you're using the cometic gasket its already .003 thiner than an oem to help with the port timing bennifit, but if the jug ur playing with still has "scallops" you're blowing the power out the pipe early anyways

just seen this post... http://www.bannedcr500riders.com/board/ ... 1138#51138

exactly what i just explained is taking place on glens port work here! it has been decked, but there is no way that piston is up that high on decking alone.

I don't think using thicker base gaskets is a bad idea actually and have done it to a TRX 250r once and had good results. Not as good as porting but it was very noticable. Stock gaskets are .020 thick uncompressed so going another gasket to double at .040 I believe on the degree wheel proves to be at least 1 degree of port timing but I think it was even more than that. I didn't check mine when I had it apart but when you have stock porting with the single base gasket I believe the piston top was just slightly above most of the ports at bottom dead center. Even if the crown of the piston went below the port floors a bit that isn't going to hurt anything. If I were to this route, I would turn the top of the cylinder down to bring the piston to zero deck height at top dead center. I would also call Cometic and see if they have a .040 thick base gasket so you didn't have to glue two stock gaskets together. This would be a real cheap way to get a bit more top end power if this is what you wanted. This along with a little casting flash clean up and opening up the boysen ports would probably be a good all around mod.

Roostius_Maximus wrote:just seen this post... http://www.bannedcr500riders.com/board/ ... 1138#51138

exactly what i just explained is taking place on glens port work here! it has been decked, but there is no way that piston is up that high on decking alone.

i just had my motor apart few days ago, i didnt measure deck height but it seemed like there was roughly -.020.....so if brit had .020 shaved off, then he would have near 0 height. from brits photos it appears he has 0

.020 is alot to cut if you're just making the surface flat!
the piston is also above the deck so its had more than .020, and if the head is cut alot then its going to be time to hit.
You'd never hit anything cutting .050 total on a stock 500!

Its gonna be making that nice bding bding bding noise tomorrow


Its running faster than ever and I aint fuking with it

Roostius_Maximus wrote:.020 is alot to cut if you're just making the surface flat!

when brit got the cylinder it was brandnew on standard bore . im skeptical of this whole situation. would be interesting to see what the final analysis proves to be the cause

100hp honda wrote:anybody have pro or con opinion on using 2 base gaskets ?

What is your desired outcome of this?

one additional gasket will do very little to change the port timing. as for compression it will drop slightly, just a few percent from using one. just try it if you are interested, ride it and let us know.

south central hoon wrote:

100hp honda wrote:anybody have pro or con opinion on using 2 base gaskets ?

What is your desired outcome of this?

was just a thought in the grand scheme of things