How to lower compression on 10mil 72mm bore bike.

[JUSTWANNARACE]

2 minutes ago, Ayesully810 said:

haha wow.  thats a lot of work, I figured lots of welding i could tell from looking at the cyls that have been welded on a ton.  how do these compare to a 10 serv or cub as far as how they ride? 

Cub or serval is going to make more power all the way through on most of those old builds(there where some over achievers that would walk on a cub of the same size, but very few) problem with the old school stuff is limited transfer volume. They would also break out around the outer rear cyl studs. And crack around the transfer ports. But in the day that's what you had to do to be the fastest on the hill..

[gusto]

This is a cool thread. That’s all 

[bricktop2011]

19 hours ago, gusto said:

This is a cool thread. That’s all 

A few pics of the 10mil X 72mm.

 

 

Cylinder appears to be sleeved with O-ring cut in. Piston is 423P6 72.5mm jetski piston

 

 

 

Bottom of the head, showing chamber width

 

 

Top of head showing closeness of inner holes

 

 

Approximate center to center spacing of head studs

 

Piston protrudes from deck approx 1mm at TDC.

 

BDC and ports

 

 

[Ayesully810]

dang you think with all that welding and stuff they did they might as well as made it a triple exhaust port while they were in there lol 

[gusto]

Wow that's a lot of time and effort to make that cylinder! Thanks for the pictures. Do you know if the builder of this engine is still doing banshee work?

[Ayesully810]

apparently this is Chad from Holeshot racing

https://www.google.com/search?q=july+1991+dirtwheels+magazine&source=lnms&tbm=isch&sa=X&ved=0ahUKEwijzaXhnfzaAhXixYMKHQY2AfUQ_AUICygC&biw=1440&bih=769#imgrc=86rS-p6kjwMx9M:

[JUSTWANNARACE]

Chad spent some time in the pokey but he is around and does some work here and there. And yes that is chad on the cover of that dirt wheels. Chad started with Jim duncan(JD racing) then when out on his own later after jim got out.  I have actually set up quite a few of those in the past myself. Alot of time and work. Matter of fact I still have a few sets of sleeves to do that setup.  People didnt start doing triple ports till the late 90s early 2000s.. you can make as much if not more power with a properly ported single exhaust it's just hard on pistons cause it wants to shove the piston through the exhaust port.

[JUSTWANNARACE]

And I almost bet if he took a pic of the intake side it doesnt look like a stock banshee cyl either, more like a 250r style intake (cub style), lots of welding and porting on the intake side also. Or, being chad did it, it may be an oval port intake. But that one I would bet more on the 250r style. Geez the work we used to have to do to go fast..lol

Edited May 11, 2018 by JUSTWANNARACE

[gusto]

Great and interesting info JWR!

[Ayesully810]

This makes me feel so young haha hey brick top you should pop those reeds out and snap a pic of the intakes im curious now.

Edited May 11, 2018 by Ayesully810

[bricktop2011]

13 hours ago, Ayesully810 said:

This makes me feel so young haha hey brick top you should pop those reeds out and snap a pic of the intakes im curious now.

Sure thing. I should be able to get to them in the next day or so.

So back to my problem, I am thinking a cool head would be impossible, probably never find one to fit the stud spacing, and I don't think its a good idea to try and seal an O-Ring against another O-ring.

Re working the chambers sounds correct, and I left a message for Louie, but have not heard anything back yet.

For a less permanent solution. how about a thick gasket or machined spacer between the head and cylinder? Is that a reasonable idea? I read that once Vitos made a 2mm plate, but I don't know if that would be thick enough or would even seal with an O-ring on one side but not the other.

Thanks again for the great info guys, here is that pic with Chad. Has anyone ever attempted to scan and archive those old Dirt Wheels magazines?

[ginger]

the problem with the spacer is it will cause a place for it to leak.  

 

Not sure if they make a thicker head gasket but you could get by some with that.  i dont think it will be enough to bring you down to pump gas range.  

 

[JUSTWANNARACE]

9 hours ago, bricktop2011 said:

Sure thing. I should be able to get to them in the next day or so.

So back to my problem, I am thinking a cool head would be impossible, probably never find one to fit the stud spacing, and I don't think its a good idea to try and seal an O-Ring against another O-ring.

Re working the chambers sounds correct, and I left a message for Louie, but have not heard anything back yet.

For a less permanent solution. how about a thick gasket or machined spacer between the head and cylinder? Is that a reasonable idea? I read that once Vitos made a 2mm plate, but I don't know if that would be thick enough or would even seal with an O-ring on one side but not the other.

Thanks again for the great info guys, here is that pic with Chad. Has anyone ever attempted to scan and archive those old Dirt Wheels magazines?

Shoot me your name and # and I'll send loiue a text and ask him to get ahold of you on monday

[n2otoofast4u]

Holly fucking old skool cool!!!!!

 

 

[trickedcarbine]

15-20 years ago, this thing was cutting edge. It belongs in a 90's neon themed machine. Way cool for an old stock cylinder set up. I've still got my old 7mm big bore stockers and just can't seem to justify the cost to get them set up again.