White Smoke

[alexbrown64]

Had a great day out at Ducks Nuts Ride Park 2 hours out of Perth. Went with a mate who has a CR500.  I took both my YZ125K's.  Run the yellow one in with its new ProX piston.  However, after about 30-40 minutes on each bike, they both blew white smoke and died. Still kicking over but no life.  I pulled the plugs and both had antifreeze on the plugs.
A couple of things... i used a torque wrench to torque up the yellow bikes head (18ft/pounds 25nm).. but it never felt very tight. The white bike had a lot tighter head nuts using a 12mm spanner "hand tight".. both done in a crisscross pattern.
The white bike had the rad cap swapped out for a 1.6 bar one, as i was loosing fluid through the overflow. 
Both bikes use after market Mitaka head gaskets.

Just wondering if you guys have any idea's on what can cause the problem with both bikes. Does anyone use yamabond either side of the head gasket.. could the head studs be stretching, cap holding too much pressure, bad quality head gaskets, head not tight enough, any other things??

Will order a few OEM head gaskets anyway, but i also have a few more new Mitaka head gaskets.
I haven't pulled the heads off yet, as we only went riding today.. is there anything i should look for?
Did some research tonight and Wiseco do produce a 58mm head gasket.  Have put 3 hours on this top end without a problem, but perhaps with the higher pressure cap, something has let go. Will also order the W4053 gasket kit.

One other thing... the white bike has a 2mm oversize piston. Have been using a stock size head gasket. 

Cheers guys...

[Tomas]

It may be a good idea to warm engine up let it cool down and than retighten head nuts.. Not doing so can cause head gasket to leak.

[alexbrown64]

Thats a good suggestion Tomas, thanks.
I am going to rip the heads off today and have a sneek peek.
Body is aching like hell today (Sunday), from the ride Friday!! Bloody old age!!

[alexbrown64]

Pulled both the heads and both have blown through the head gasket at the rear.
Pic below...

[tony27]

Strange place for them to go. Do the bikes run head stays in about that point?
Try rubbing both head & barrel on wet & dry sitting on a piece of plate glass to see if 1 of the 2 has a low spot

[alexbrown64]

No head stays on these cylinders tony.  I will give the heads a rub on a flat surface with 400.  The yellow bike has had a machined head and cylinder only 2 hours old by Eric Gorr in America.

[smed]

Maybe the head gaskets , I have a Mitaka rod in one of my bikes & clutch baskets, plates & springs in 2 so rate there products but never used there gaskets, not for any reason just never did, Are you using the correct head nuts not the acorn type?  They can bottom out on the threads before pulling down properly on the head, they will torque up of course but the force is on the stud not the head, Old bikes hey, just when you think all is good they pull some other crap on ya   

[Lozza]

I would be extremely surprised if the top of the cylinder is completely flat, (don't ask how I figured this one out) but sometimes when a cylinder head gets machined flat it exposes a ever so slight divot in the cylinder deck. I presume the head had a corresponding high spot before machining. Unusual at the rear of the  cylinder as it usually happens over the exhaust port. Pull any head studs and rub the deck on 600 wet and dry on glass, the shiny spot will be the low spot

[alexbrown64]

Thanks for the input guys.

I have ordered 2 oem gaskets as nos from Ebay.  Will rip cylinders off and rub the cylinder and head with #600 on glass.  Will also get all new cylinder studs, as these ones are 34 years old.

Lots of work to do on these bikes again. Yellow one had a flat tyre.. plus it was too big (110/100), so its getting a 100/100. Forks too stiff and seals leaking, so new seals and drop oil level.

Front brakes on white one need sorting.  Yellow one has DLS, white one needs. I will get some OEM organic pads and ARC them.

The list goes on.....

Cheers,