Hi there! my bike is at my local mechanic workshop....

One problem is already known...the chain that is inside the engine, on the cylinder, broke!

Tomorrow the engine will be split to see if any more damage has happened........ Hope nothing too serious still, new piston is almost certainly go in.... +0,50 and 11,5 : 1 compression ration

Did you get in the piston yet? I'm curious about the power increase. I've been thinking about putting an 11.5/1 compression piston in my bike.

Hi Micah...noup, haven't put it yet... I'll only do that when I have to rebuild the engine... which I'll probably include a stage-2 cam

Vando

Keep us posted on that. If my engine blows, I'll probably be looking to do something similar.

Well.. I just had to get new: two intake valves, the camshaft chain and all the necessary gaskets (all from Yamaha)....

It's gonna be a few years before I do have to rebuild the engine I HOPE!

Have fun!

Vando

Oh man, i'm sorry to hear about your engine damage...hope it will never happen to anyone. You should also take a new cam sprocket, as it should be changed with the new cam chain.

On the topic:

The higher compression piston, with the increased bore, will give some real power gain.

I'm using a Wossner 12.4:1 95mm piston, with an regrind camshaft (about 1st stage) and it worked fine.
Now i'm going to put a 282o/10.8mm cam, Ti retainers and uprated springs. I hope i will be soon ready to post my opinion on this stage of tune.

I've been thinking about getting another XT and tuning it out like this, any opinions on the high compression piston and performance cams? How good is the power gain? Are we talking 50hp+ at this point?

I've recently seen a XT600, with 101mm piston, 11.5:1 compression, Stage 3 cam, double keihin FCRs.
The "thing" pushes 63hp at wheel!


My engine, never had a problem due to hi-compression, the 282o cam let ti idle at 1700rpms and there is a lot of power, at all rpms. (i go up to 9k sometimes...)

Holy crap!

So are we talking roll on wheelies in second gear if I do the high comp piston and maybe the cam?

It's been about 8 years and ~40000 km now since I sported for the 96mm 11.5:1 piston.

Here's my thoughts:

That's way more compression than it needs. It's an XT600, and it's beauty is in it's simple ability to keep running. There is more at play though: as a big single it's weakest point is it's top end so by increasing the compression we weaken it's weakest point. Also, higher compression makes more heat which is not good for air cooled, and the premium fuel it needs isn't always easy to come by.

There's significant piston slap on startup till it fully warms up. Forged Wiseco piston (forged expands more than cast pistons, so piston/bore tolerances are looser) + air cooled (air cooled makes more heat, so piston/bore tolerances are looser) = a clacky bike. A loud exhaust helps solve this problem.

I've blown two head gaskets with the high comp piston. Last time it blew I had the head decked, ported, and valves seated. Now it's seeping a bit of oil at the head gasket again. She's a durable beast though, so she'll keep running till I buy the next oversize.

When I do it over, 9.5:1 compression will be with my next oversize. The XT is an "all around motorcycle", capable of trails, touring, cruising, or sport, a master of none of them, but well suited at them all. With that said, my next horsepower upgrade would probably be an extra cylinder or three.

Well said, reliability is the name of the game. If horsepower is what you want, get another bike. I prefer my 86 with 15Kmiles and still has 170 psi compression on a new gauge. Solid as a rock, stock as new save a Zeeltronic CDI to replace the dead OEM one.

If horsepower gains are not done right, you waste your money.

My opinion only...

__________________
'84 XT600 is now bored to 2nd oversize and new OEM pistons and rings installed. No more smoking.

Thanks for the info, mine as still on the shelf and will be there..I bought another bike for the extra power

mmm, got to disagree with many of the comments here, first, +2mm means +20 cc, not 1-2 cc... but most of your gain will come from the increased compression which in thermodynamics terms, means better efficiency, i.e. getting more power form the same amount of fuel. it's a big subject, do some reading on thermodynamics of internal combustion engines.

the improved motor response with higher compression starts already from low revs and you will certainly notice it. the main reason high comps can run hot is because people often install these pistons without checking squish height. this is hugely important to avoid detonation which overheats the engine. bring squish down to around 1mm, not more and youll be pretty safe. agree that this doable only if you can get decent gas, not a good idea if you are planning to go to remote places.