Okay, so I thought I'll do an engine rebuild this winter. Sucks, I need it NOW.
Yesterday, after a ~2km stretch of ~140km/h it started knocking a lot louder. It had this noise, but not nearly as loud (still isn't as bad as it might sound from what I tell, but I don't want to ride it like this any more).

I haven't opened the engine up yet, but I am looking at various parts options.

So anyway... What to buy?

Piston. I'd like a higher comp one. Between 10:1 and 11:1. Or maybe just got for it and buy an 11,5:1?
Here's two options (looks really good actually)
Wiseco Yamaha YFM600 YFM 600 Grizzly Piston Kit 98mm 3mm 1998 2001 4607M09800 | eBay
Wiseco Piston 96mm Oversize Yamaha 4596M09600 | eBay
I'm not sure of the diameter yet though. Will know that after the disassembly.

Gaskets. What gaskets to buy and from where?
Oil seals. The same as gaskets...
O-rings. I think I can get them at the local hardware store, if they won't be included in the gasket set.

Bearings. Are there any specific ones? I might not need to change them, but still...

Connecting rod. Well I don't know in what condition it is in now, but still, any options?

And so on... Stuff might get done later on, like a stage 1 or 2 cam, but the original one looks very good, so... Will stay for a while.

I might look like a headless chicken, running around without knowing where to run, but heck, I need your help and experience

Hi !
I would go for oem head gasket, but try to source one from somewhere other than a main dealer. Mine was £54.00 and i paid it cos i was desperate to get the bike back on the road. Ive since got a couple nos ones off ebay for a lot less to use if and when theyre needed. Cant help you with anything else but good luck with the rebuild and keep us updated


Bill

Since I'll probably need an oversize, won't the OEM gasket be too "small" for the larger piston?

Im guessing it will be yes! Missed that bit of your post. Oops

Since I want to still be able to run regular pump gasoline and I don't want to have a low moto-hour engine, I'll probably stick with the 10:1 comp piston. It's on a "sale" right now, link given in the first post. It's a 98mm piston though...
So, what should I do with the gasket?

If you're staying original piston size, go for either genuine or quality pattern.

I've used loads of Athena head gaskets and gasket sets and never had a problem. Never had one come back.

Like many things in life, it's all about the prep work. Those mating surfaces need to be beautifully clean and smooth and most importantly, FLAT !!

If you're going for an oversize (which I think you will end up doing) then you're best off to get an oversize head gasket. I think you're better off with genuine Yam if you're going oversize too. You don't HAVE to go oversize with a head gasket but why wouldn't you !!

To be honest, when it comes to oversize stuff, I always go genuine as you will know it's been properly measured and tested.

I don't know you're level of experience but if you need to go oversize you need to get your barrel honed out (usually 0.25 or 0.50mm bigger) Eg, if you go 0.25mm bigger.

You need an oversize piston 0.25
Oversize rings to fit 0.25
Oversize head gasket 0.25

Same deal if you need to go 0.50mm over.

If you're barrel and piston are totally goosed then you might need a new cylinder sleeve putting in. Then you're back to standard sizes usually.

Hope that helps.

Ted

__________________
Did some trips.
Rode some bikes.
Fix them for a living.
Can't say anymore.

You need to stick with an XT specific piston whichever size you get. The wrist pins are not always in the center of the piston, many are offset some to prevent tipping and knocking at TDC. The XT600 is centered but I don't think the Grizzly's are.

You said you haven't taken the motor apart, how do you know the cam is good? If it was starved of oil, even for a short period, the cam and its corresponding rocker get wiped out and make a bad knocking/clanking. The other is timing chain slap. Doesn't mean the bore is bad or needs to be redone. Though if it is dug into very far it is nice to just make things new and tight again.

If you wanted to you can just get a new sleeve and drop it in your cylinder, have it bored to stock size and re-use your piston with new rings, it comes out just a little cheaper that way but it is stock compression though. There are way to up it but it involves more machining.

If your looking for a power boost, the hi-comp isn't going to get as much as you'd think with the stock carbs. You'll gain way more usable power with a stock topend but better carb(s) than an improved topend and stock carbs.

Ted,

I'll probably go with an aftermarket gasket set. But I can't find an oversize gasket, unless it's for a 101mm conversion...

I'm rebuilding oldtimer motorcycle engines/gearboxes "for living", so I know everything there, where to get what and at what prices, but the XT's engine is a new to me. So I don't want any screw-ups.

The piston is "dead", read on for more...

jjrider,

the piston in the given eBay listing is noted as compatible with XT600/SRX600/etc. so it should be okay. Also, the part number 4607M09800 looks to be the same as the XT600 piston. So it's the same piston, just listed under "Grizzly/Raptor" title. As far as I understand...

I looked at the cam through the valve adjusting covers, haha!
But now the engine is apart and I can say 100% the cam is in very good condition.
Cam and rockers are 98-99% like new. The cam chain has some play in the links, so I might change the chain and sprocket in the same go.

However the piston is "dead" as mentioned before, it has two cracks and the cylinder has some serious scoring. Also the piston ring gaps are way too big.

Another question/asking for opinion:
my con rod bottom bearing is like new, no play what so ever, but the top hole where the piston pin goes in has some slight scoring. The piston pin (old one) has some play in it. Should I change the con rod or wait for the new piston and pin to arrive and check for play with the new pin? Check pictures.

The bike has Raptor 660 carbs, re-jetted and with aftermarket needles, K&N air filter and some Yoshimura carbon fiber exhaust. So little by little I want to make it better, even if the high comp piston gives me just a bit more power/torque

My XT's threads are here:

http://www.horizonsunlimited.com/hub...lization-64290

and here

Yamaha XT 600 personalization - ADVrider

Pics:

Kedo should have a 98mm gasket for the bigger piston.

I just finished rebuilding my 87 XT600 engine. Don't worry about the headgasket size, the stock gasket will be fine, unless you go crazy on the over-boreing. You sir need a new piston and bore. Take the bore out and send it to a machine shop (Stock bore size is 95mm) and have them mic it. See if you can bore it over to 96mm. You will need to check the crank for up and down play (a little side to side is normal) on the big end, and also mic the small end on the rod. Make sure it's within clearance. I personally went with a 11.5 Wiseco 96mm. Also check the transmission, as these bikes have gear issues. Open up the oil pump and check for scoring marks. Just give it a good once over. I ended up having to replace 1 case roller bearing, which was for the output shaft.

I'd double check the piston deal, Raptor pistons I know are offset(I have a motor build using both model parts) but the XT's are not. The Grizzly 600 might just be the same as the XT, never had one, but the Raptor part isn't right.

I do have a pile of good oem pistons I don't need.

I wonder how your piston got cracked like that. Pre detonation .

Hi Zergman
others here have been disappointed with the fitment of aftermarket gaskets, not sure if that included the head gasket?

Bob

__________________
Remember that Assumption is the mother of all f**k-ups.

I got the Vesrah engine kit, the only gasket I didn't like was the paper cylinder base gasket! Didn't fit perfectly.

Thanks Jens, but Kedo has a 99mm gasket. Not sure what I'll do, but maybe I'll go OEM size...?

AnthraxBird, don't make me regret going 10:1 I would love a 11.5:1 but I'm not prepared yet for the crank durability and fuel octane questions, yet...

I've ordered the 10:1 98mm 4607M09800 piston, it has to fit.

How the cracks were done I don't know. Maybe due to piston slap - lack of lubrication when the scoring was done, maybe pre-detonation, but there was no pre-detonation except on high rpm in neutral gear, it was shooting sometimes (only sometimes...). Don't know why.

Still wondering if I'll need a new con rod.

Think you may want to look fairly carefully at the lubrication circuit,starting with strainer and pump.
There's a good chance the small end of the rod is excessively worn looking at the plight it all seems to be in.
This was the cause of the clatter on mine when I first got it.
I used a genuine yamaha rod and big end,wossner piston kit,main bearings, the usual gearbox parts and bearings and fitted a used 3aj oil pump,recut the valve seats and that was about it. 20,000 miles on its still fine..the bikes taken me all over Europe and been a great after a bit of a shaky start..