Somethin's wrong with new cylinders

[alcoholbanshee]

I've got the gaskets that come in the Rocky Mountain Cometic kit. Used the base and head gasket.

Check your squish..... If it is more than .045 then it is to loose. You can change this by installing a thinner base gasket(assuming you have a thick gasket now). That in turn will raise compression. See where I am going with this????????? Squish should be between .030 and .045.

[okbeast]

Yep I get the concept, just never checked the clearance. Will get it done this evening and post back up.

[370banshee]

ok with the top of the exhaust port at 27.5mm and with a stock stroke your looking at 192 ex duration.. thats a trail port.. at 800ft with a head cut .030 and the same 192 ex port.. i get 150-155 for compression BEFORE i even start it.. this is also with wiseco or cometic gaskets.. i don't see .006 of the head making that big of a decrease in compression.. actaully i see NO way of that happening.. but we ahve to figure the fact that your at 1200ft and i'm at 800ft... sooo... with the diference in eleveation and lsight variation in the head milling... you might be right bout where you want to be... i'm not sure on the realtion ship of elevation-compression.. as in... how much you lose for every 100ft.. but being that the air is thinner the higher you go... i can see this being a big factor.. i'd lie to see f somebody has a ballpark figure of compression loss over a 100ft elevation change.. but ti seems to me you should be about right.. and your right.. for a play bike a 192 port does RIP

[dajogejr]

A few PSI at very best.

Here's a relative chart near the bottom from Dave noss.

 

http://www.nossmachine.com/banshee_heads.htm

[kawiking]

i had mine drag ported and 0nly had 140 /142 on a new top end..... with a .30 thous shaved head.

[okbeast]

It possibly could be the porting, obviously every port job will re-act differently. My buddy has some Trinity drag ported cylinders and with 20cc domes he has 165/165 in each cylinder. Granted when he had it rebuild last time the builder did deck a little off the top and bottom of the cylinders, and this is why I think his is so damn high for the domes he's running.

[370banshee]

well according to dave noss's website.. for a 20cc dome there is a cahnge of 13PSUI fomr sea level to 1000'

 

so an estimate of 1.3PSI per 100ft woudl be a good ballpark... that accounts for what... 5.2 PSI and i can't see the .006 in milling difference make that much of a differnece.. seriously though... if it rips that way it is i think i;d leave it alone... does it cut out right off idle?

[Snopczynski]

I'm bout tired of this fuckin build, this thing is about to be on ebay. Put the motor back together last Saturday and got about an hour of break-in on it. Checked compression with a (what I thought) was stock head milled .040. It was at 130/130, I thought that was kinda low but I figured the rings hadn't seated yet so it'd go up. Rode Sunday at the river, pretty much like normal, didn't pussy foot it but didn't hot rod it or anything just raced like normal. Checked compression last night, still 130/130...shit.

 

I then pulled the head off to see if it was really milled, and it's milled around .024. Ok, figured the compression with that should at least be around 140 or possibly higher.

 

Had another stock head that isn't milled so I threw that on just to see and I got around 110/110.

 

Have the rings not seated yet, or is it somethin else?

 

 

Factors here are elevation, head and base gasket thickness, bore size, compression tester integrity. All need to be in place for a good and accurate reading.

[okbeast]

With 14/41 gearing, running 22" 10 paddle ultra-lite haulers in soft river sand it lagged a bit in 1st gear when I would slowly run it up to speed. Now whether this was lower compression (130psi) or the other factors I'm not sure.

 

Squish clearance #'s will be coming tonight with both stock heads. When I get a new o-ring set I will throw the 19's in and get a psi # from that. Otherwise I guess I will just run the milled head and see if anything changes.

[No Limit Powersports]

I wouldnt be to concerned about the numbers that you are getting. Your builder/porter is the only one thats really going to know where you should be without just playing with it. Exhaust height def plays a role in compression cause as the exhaust port gets raised the piston has less time to build compression but this is not the only factor to consider in porting, the transfer size and effeciency will also play a role, its really a whole package that has to be put together to work with each other. According to my calculations you should be around 192* exhaust which is fairly mild and should be a good runner, but dont discount other factors. If your head volume is around 21 and your squish was correct (around .036-.042 is where i like em) then your probably not to far off but if you think your suffering in performance then rechamber the head to be a little tighter or buy you an aftermarket head and get the domes cut to fit your application.

[2twin350s]

I think you are chasing a problem that is not there.

Both my shees are trail ported and have the heads shaved 20 thousandths.The 89 she runs 135 on new piston and rings,and my 96 shee runs 128 and 132 on new top end.I am in Ohio and elevation is around 800 feet.

I think you are fine.If your squish comes out at 60 thousandths or more,I would shave the head another 10 thousandths and that should put you in the 138-142 compression range .Also,It helps to hold the throttle wide open while doing your compression test.That will bring up the reading slightly more.If it runs good ride it.You will be fine.That is a good reliable compression to run at.

[okbeast]

Ok with the stock stock head squish is around .055 and with the milled head it is around .050, so sounds like that's a bit high, therefore explaining the small loss in compression.

[dajogejr]

Put the head with 50 on and be done. It's not that high to where I'd worry about it.

[alcoholbanshee]

Put the head with 50 on and be done. It's not that high to where I'd worry about it.

I agree it is not optimum.......but it is certainly safe!!! Put it on..you said the bike rips!!

[badassbanshee479]

sounds like a great pump gas motor to me!!