Attn DR750/800 owners

[guest868]

I currently have in my possession a 1993 DR800 with a goosed gearbox bearing. I have access to a 1989 DR750 bottom end in good condition. Are there any DR knowledgeados on here that can tell me if I'd be able to fit an 800 top end onto a 750 bottom please? Am I right in thinking the 750 has a shorter stroke?
Thanks in advance..

[Jez F]

You are thinking right, as far as I know the 750 is a shorter stroke and a slightly different piston,  but that is about all. If you swap the crank over as well as the top end it would probably work. I've got a DR750 engine minus piston, cam and rockers, plus other bits for sale by the way, stripped down as I was using it to line up engine mounts on a special that has had to be given up on for the forseeable future, any offers before it goes on ebay?
 Jez 

[guest868]

Where are you based Jez?

[Jez F]

Sunny Wolverhampton!

[Dave#22]

Hi Shed', The DR800 top end is dimensionally identical, but you will need the DR750 piston as it has valve clearance pockets machined into it. You may be able to machine pockets in the 800 piston depending on crown thickness. The reason the DR800 doesn't have pockets is that with a longer stroke and the same barrel height, it uses a shorter conrod which leaves the piston part way down the barrel at TDC to give a reasonable compression ratio and also drops the rev limit. The skirt clearances differ as well due to the 750 piston being cast and the 800 forged. And to confuse things further all O/S pistons are cast, but I think stocks of those have diminished.
   Dave

[johnr]

try asking on the dr big forum! the guy to ask is called big bob, he has a garage full of dr's.

http://www.drbig.info/tiki-index.php

[guest868]

Cheers for the replies guys, I think I'm going to go ahead and split the 800 cases to repair it hopefully, but I'll also have a 750 bottom end by the end of the week. If I end up going the 750 route then I may come knocking Jez.
John.r, how do I register to post on the DRBig forums? I can't find anything...

[Steve H]

There are two forums on the site, the 'new' one is here http://www.drbig.info/forum/

I have a DR750/800 manual on PDF somewhere do you want a copy ?
 
Steve

[guest868]

Aha! Thanks Steve. I may have a copy of the manual off you; I've got a Suzuki workshop manual in hard copy, will the .pdf show anything more?

[Dave#22]

Hi Shed', The info that Big Bob (DR BIG forum) gave you is incorrect in that the 800 barrel is 6mm taller than the 750. They are both the same height. I have a 750 barrel overbored 1mm on an 800. The only problem I had fitting it was that it had to be relieved slightly to clear the later cam chain tensioner. Conversely, the 800 engine that exploded on me 18months ago was rebuilt using a DR800 engine, 750 crank and a 0.5mm oversize piston.
  Dave

[guest868]

Cheers Dave, I've got my 750 bottom end now and hoping to split the 800 cases shortly. If I can just rebuild the 800 motor I'll stick with that and then collect parts for the 750 to maybe build that at a later date.

[johnr]

well if you fancy selling the 750 motor, ive a 250 suzuki frame thats crying out for a big single motor!!

[Dave#22]

Cheers Dave, I've got my 750 bottom end now and hoping to split the 800 cases shortly. If I can just rebuild the 800 motor I'll stick with that and then collect parts for the 750 to maybe build that at a later date.

Another thing to be careful of if you are mixing parts.....the primary reduction gears between the crank and clutch differ between the 750 and 800, fit them in pairs.
  Dave

[guest868]

Thanks for the info guys. Johnr, you can have first dibs, but don't hold your breath! I'm chasing up a lead on a dead Goose which could be a worthy recipient...