Triumphrat

andymac · 10-15-2008, 04:02 AM

Hi all,

After reading some posts about the performance increase of the 904 big bore kit, it seems the improvement is due largely to the higher compression pistons.

It seems a little over the top to go to all the expense of new liners and machine work involved for a lousy 39cc over a stock 865.

Has anyone just installed high comp. pistons in an 865?

Cheers,

M700R · 10-15-2008, 08:43 AM

I like the way you're thinking here... Good question. I don't have the answer, but will watch this thread...

sweatmachine · 10-15-2008, 10:04 AM

Thrux-ton-up had special 11-1 pistons made that fit his stock 865cc bore.

Mallkolm · 10-15-2008, 10:09 AM

Quote:

Originally Posted by andymac

Hi all,

After reading some posts about the performance increase of the 904 big bore kit, it seems the improvement is due largely to the higher compression pistons.

It seems a little over the top to go to all the expense of new liners and machine work involved for a lousy 39cc over a stock 865.

Has anyone just installed high comp. pistons in an 865?

Cheers,

Or is it possible to get the same results by skimming the head? Then you don't even need to lift the cylinder off. And you might as well get the head ported/ flowed at the same time!?

/Mal

mag10 · 10-15-2008, 02:28 PM

.050 or .060 inch of the head should do it. pretty low cost way to get more power. investment would be just gaskets and your labor. the charge from a machine shop for this would be small (your do it yourself)

sweatmachine · 10-15-2008, 04:23 PM

a few problems with skimming the head:

you can't unskim it
you can't fit larger valves later on down the road without clearance issues
the stock cast pistons weren't made with higher comp in mind

Really, the wiseco kit can be installed for well under a grand if you do it yourself, and it includes FORGED pistons with large valve reliefs. Hard to beat.

Bonnie1000th · 10-15-2008, 05:45 PM

Quote:

Originally Posted by mag10

.050 or .060 inch of the head should do it. pretty low cost way to get more power. investment would be just gaskets and your labor. the charge from a machine shop for this would be small (your do it yourself)

If the head get skimmed 0.50 or 0.60 , a beautiful hole will adorn the pistons crown in no time.
WRONG ADVISE!

mikeinva · 10-15-2008, 08:46 PM

allso if you cut the head much your timing chain wont line up right.Why would you want to stick new pistons in a old bore ?The bores on these bikes are coated not like iron jugs you can just hone or bore alittle.By the time you pay to get pistons made up custom you will have paid for the 904 kit anyway.

Mallkolm · 10-16-2008, 02:40 AM

with comments against skimming from authorities like these two gentlemen I guess we can rule out that possibility...

Man, I thought it would work so well.. considering the Commando Combat engine!

andymac · 10-16-2008, 02:56 AM

Some interesting ideas, but my whole point was to get away from any machining. I'd definitely opt for the 904 kit before machining the head and possibly opening up Pandoras' box.

My bike only has 5000 kms on it so the old bore scenario doesn't apply.

I'd imagine there is a piston available to suit one type of bike or another that would fit, a little more research is in order...

I think if Triumph had just lumped in an 1100, we'd all be a lot happier and richer!