cylinder gasket - YZ vs WR

Anyone used thinner yz cylinder gasket on a wr?

It is almost half as thin so i dont know whether it is usable on wr.

Would increase compression probably but would also put valves closer to piston.

And since yz head and cylinder are diffrent product codes from wr, puts the situation even more into unknown.

Asking about older 400, 426's.

I don't know what you are talking about?

The cylinder and gaskets are the same for the WR400 - YZ400, and the WR426 - YZ426.

I thougt also, but

YZ400 cylinder gasket product code is 5BE-11351-00-00.

Wr 400 cylinder gasket product code is 5BF-11351-00-00.

Head gasket also differ in codes, but visually look alike.

Measured both cylinder gaskets, WR 1.1 mm or 0,043 inch and YZ 0,6 mm or 0,023 inch thick.

not sure about the WRs but i know on the DRZ400s it is a common modification. people will use the "E" model base gasket on the S & SM models to slightly boost compression.

one would have to take squish measurements to be sure the piston to valve clearance is within spec with the thinner gasket. if it works out it would be neat to see what difference in power the extra compression would add.


You're probably right.

Took pics recently, to see the diffrence, both are original yamaha parts.



To revive older thread.

I'm now into replacing the 3rd OEM cylinder gasket, because it gets a blow-by.

Oil or water blow-by, sometimes both.

Don't exactly know what to blame, but:

-when doing upper end and torqueing the head bolts to specs, should the torque be checked after few hrs of use? Book doesn't say it, neither does Clymer manual.

It blows at the front end of the cylinder, sometimes tears the gasket, sometimes just hissing water by the gasket, when bike running hotter.

Can not really resolve the problem, since every occasion is a bit diffrent, but location is pretty much the same.

Gasket is quite thick for the WR, and probably the o-ring at water passage doesn't get squeezed enough. First water, then oil...presume.

Each time I rebuild with new gasket, I get approx 10hrs of good riding, then a blow by.

So much for that.

Use new o-rings each time as well, and have both the head and cylinder surfaced at a machine shop. Once you start to get blow by, the surface erodes just a bit and makes the entire area a bit more prone to leakage. For wat it's worth, i am running YZ gaskets on my WR without issue...I didn't even know they were different, I ask my dealer for YZ parts because he's more likely to have them in stock...

Problem is, it blows below cylinder, not cylinder to head connection. Upper area I've had resurfaced and new o ring every time.

I believe it is hard to resurface the bottom surface of the cylinder, since the cylinder wall sticks out, but probably the gasket is there to fix minorities.

Will provide pic of the dobtfull area.

I'm pretty sure the prefix just identifies the bike in the fiche but the numerical portion of the code identifies the part number - making the part numbers identical.

I also recently redid my engine and bought a Moose Racing gasket kit that was made for WR and YZ bikes

Check it out - same gaskets for top end rebuilds etc....

If you look at 98 to 00 Wr's, they have identical gaskets FOR SURE, but the part numbers have a different prefix. Just like valves etc and they are all the same YZ or WR......

That's probably true as I can see on your link YZ WR 98 99 are the same, but I got originally sealed yamaha OEM cylinder gasket, its code matching the YZ 400 98 and it is more than half thinner than WR 400 99, I order from my dealer.

That's why I'm not sure if to install it, because I'm not sure of tolerances piston to valve.

Check the lower pic, showing already installed WR gasket, and beside it, it's the YZ gasket.

At the area where the chain slider is, the thickness diffrence is very obvious.

Presume thinner gasket would solve the blow by problem, because it squeezes and expands less, but would the piston hit the valve or would compression be too great for the old engine, i dont know.


The one you're holding next to the bike actually looks a lot more like the one I installed in my WR - let me check tonight and see the thickness, but what's installed currently looks way too thick.

Also - what I pulled off my engine was identical in thickness to what I put on.

I really think 1.1mm is way too thick - it seems to be twice of normal, look at what the thickness of a high compression gasket for the YZ/WR is - 0.012" = 0.3048 mm - high compression gaskets work with stock piston and head for low cost performance gains.

Your THIN gasket is twice as thick as the high compression gasket above, and the "other" gasket you have is 4x as thick..........leads me to thinking your .6mm gasket is the actual proper gasket for the bike....

Oh, and if you're worried about touching valves - don't be, there's more than enough clearance up there even with everything moving, remember - you can hold your Decomp lever open right through the TDC stroke (ever see how much it moves that valve). - a lot more than 1mm

Thanks a lot for taking time to measure yours.

Really releaved, to hear about the thin and even thinner gasket not interfearing with piston to head position.

Measured again, thinner is 0.7 and thicker as said 1.1.

Not twice as much but pretty much.

This means yamaha sells faulty gaskets, probably just for Euro market as US are 0.7.

I ordered the 0.7 from US ebay. This explains it.

Previousely I always used thicker ones calculating average 50% blow by in total in all years of service.

Checked it last night, and I can't give you a precise size because it's on the bike, but holding a vernier caliper next to it and setting it so it encompasses the gasket edges still puts it way under 1mm - closer to the .5mm side that then 1mm side.

I'm not too sure what you mean by:

Previousely I always used thicker ones calculating average 50% blow by in total in all years of service

Blow by is what happens on worn out piston rings - I think you've been using "blow by" as a term for a blown gasket - that's ok though! :excuseme:.

You will be fine running the .7mm gasket and like you had stated earlier - it may fix your lower gasket leak.

I wonder if with the thicker gasket, you have to use a higher torque value on your cylinder bolts.........would kind of make sense, and after blowing out 3 gaskets, it's either a problem on teh castings or a torque issue.

Yes, by blow by I ment leakage under cylinder, couldn't find appropriate term and since oil and water blew by under, I took it. ; )

Presume you have 0.7, and torqued seems thinner.

About using more torque, you just shoot some enlightning information. '98 models needing 4.4Nm for head bolts and '99 just 4Nm.

I took the higher value due to past experience, but shoud probably go even higher.

Also when unscrewing the 4 bolts, they didn't seem so torqued as when I torqued them.

Must say that head gasket never gave way, but it also has those 4 extra nuts to keep it in place.

Probably cylinder gasket being too thick, sinked under load, creating less torque on the bolts, not sealing enough after some use.

Thats why I wondered if after some hrs of riding, head bolts needed retightening, but the manual nor Clymer book don't mention it.

Will go with thinner, new orings and see what happens.

Wow, it all seem easy, when fellow riders around U think logicaly, thanks.

Managed to get the pic, before removing the gasket. At two locations, swelling can be spotted.

Just had a visitor, who said, doing his gaskets in plumbing or heating, he installs them completely dry on dry surface.

In my case, it could've been oil, ment for lubing piston to cylinder first contact, dripping onto gasket area and when tightening, pressure squeezed out the gasket, and consequently pressure from use did its job, until "blow-by" occured.



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