Topic: Big Bore 750 Base Gasket Question.

[754]

I was thinking of running a smaller bore than engine last had.
 Just wondering , it will probably be harder to keep a base gasket in it?

 I assume once you are past 836cc, and you have gone to sleeves, you no longer use an O-ring at bottom of sleeve.

 Now I have cases bored out to fit 1080cc, but plan on running 970cc. So I am thinking, install base gasket on case, lower barrels, and scribe the gasket, then cut to fit fairly close to the sleeves.

 It does not sound ideal, but hope it works, any thoughts? Or anyone try deboring a 970cc or larger motor?

 I could press on aluminum shims over the sleeve hanging out to make up the size, maybe.

[Jerry Rxman Griffin aka MuthaF'er]

Don't see why you couldn't carefully cleanly cut the gasket. Don't believe I'd shim.

But on the other hand, why are you downsizing?

[754]

Ha, I want to ride it on the road.

 Plus I got brand new 970cc pistons..
 But I am thinking if I went as small as 836 (have all the parts), I could throw it together quicker.. way less work..IMO.

 To me a 1080 unless it has custom barrels, is a town motor..

[NitroHunter]

Are your 970 sleeve base ODs smaller than your 1080s?
I noticed that trimming the base gasket was an exercise in patience...
Once I got it trimmed correctly (multiple tries - hey, I was young) it never leaked.
My first big bore was 970 for the same reason, thinking about heat dissipation, longevity, and the 'what if' overbore thing.
When I added the turbo, went to the track, and promply melted an almost new set of Arias pistons (due an ill-timed *!#@* fuel pump failure - note to self: don't scrimp on the important stuff) it became a 1000...
Plus you KNOW if you put in that 836 kit, you'll just be thinking about the 970 everytime you twist the throttle! 

[754]

The cases are bored to 75mm in the sleeve area.  Dont have my tools here, but I think the 970 sleeves are 3.00 or 3.025.


The big bore cases are the 69's.  I was thinking of trying to put it together in some form , to still ride it this year.

I dont really want to throw it  (970) together in a hurry and regret it, or cut corners,  but and 836 could be done  much easier. I just got a new set of Arias 970s, they look pretty nice.

 I am doing a bit of work on some funny car parts, the guy said he  knows the owner of  a piston company... looks like Hemi pistons are probably cheaper than our bike pistons...

[MRieck]

Are your 970 sleeve base ODs smaller than your 1080s?
I noticed that trimming the base gasket was an exercise in patience...
Once I got it trimmed correctly (multiple tries - hey, I was young) it never leaked.
My first big bore was 970 for the same reason, thinking about heat dissipation, longevity, and the 'what if' overbore thing.
When I added the turbo, went to the track, and promply melted an almost new set of Arias pistons (due an ill-timed *!#@* fuel pump failure - note to self: don't scrimp on the important stuff) it became a 1000...
Plus you KNOW if you put in that 836 kit, you'll just be thinking about the 970 everytime you twist the throttle! 

They are the same size

[754]

Yeah, i just did the conversion, sounds like they are the same., but what happens if you want to run 836?

[NitroHunter]

With an aluminum collar around the stock sleeves, would you need to anchor them to the underside of the block?  I just wonder if they wouldn't heat up, expand, and slide down the sleeve into the case?

[Jerry Rxman Griffin aka MuthaF'er]

Frank,

I have a set of 1080 cylinders set up for the piston I posted. I can get a measurement for that if you need it.