2 x YZ125 with blown head gaskets

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8/26/2017 7:47 PM

Hi,
Took both my old school YZ125's out to a ride park yesterday. (1983 K)
Both blew the head gasket in the same spot.. at the back. Both started puffing white smoke after about 40 mins of medium pace riding. Bikes were not hot, in fact i was still running one in.

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.

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


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Cheers


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8/27/2017 6:50 AM
Edited Date/Time: 8/27/2017 6:54 AM

Im not sure about YZ's but some hondas had a problem with the top of the cylinder not being flat. The fix was to remove the studs and surface the top of the cylinder and bottom of the head. Before I resurfaced it I also blew a head-gasket then once resurfaced it never did it again. It took some time with 1000 grit and granite slab but it worked

Also make sure all the studs are tight in the cylinder. I have been torqing down head bolts only to realize that the stud wasnt 100% seated. I use red thread locker.

Throw those other head gaskets away. OEM is the way to go.

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8/27/2017 4:36 PM

Cheers Hondas4Life3

I have ordered some oem head gaskets. A bit rare now, but they do come up on FleaBay.
Will resurface the cylinders and heads and check studs.

Have you ever used a higher pressure cap?

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8/28/2017 5:58 AM

You didn't post what type of fuel you are using, with the crappy pump gases we have today excessive ethanol can make your engine knock , which will destroy your head gasket.

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8/28/2017 9:34 AM
Edited Date/Time: 8/28/2017 9:36 AM

If it has 2mm oversize piston it may need a 2mm oversized gasket as well (im not sure) I use the Tusk 1.8 bar (I think) cap that has a temp sensor incorporated into the top of it. Never had a problem with them.

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8/28/2017 12:05 PM

I blame the aftermarket gaskets.

In my experience, wiseco gaskets, prox, and cometic gaskets have been the only aftermarket brands to line up correctly and even feel high quality. Go oem unless you absolutely cant.

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2009 Kawasaki KX450F
2009 Kawasaki KX250F
2002 Suzuki GSXR 600

8/28/2017 9:52 PM

Just throw some rtv in there and you should be fine

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Hope for the best, Prepare for the worst.

8/29/2017 1:07 AM

Cheers fellas.. i am in Oz, i think the pump fuel i use does not have ethanol. If they blend ethanol in, they have to label it E85. I did however use regular fuel this time instead of the higher octane premium (being a tight wad).
I have ordered two oem gaskets.. but i may also go for a 2mm oversize Wiseco gasket for the white bike.
I am ordering all new oem cylinder head studs nuts and washers. Will clean all threads out and seat them with red thread locker. Going to mill all parts down with some 600 on glass. Wont bother with the rtv ;-) although that suggestion did cure my mates 89 YZ250 coolant leak through his head studs. I am using a 1.6 bar on one and a 1.1 on the other, but may get another 1.6.

Hope all that is a solution..... thanks everyone for the input.. :-)

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8/29/2017 3:54 PM

I like your Lechien replica. Nice bike!

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Braaapin' aint easy.

8/30/2017 4:31 PM

Thanks Falcon,
They both took a few years to build up, but the Lechien bike had a lot more put into it. Jemco cone pipe, Race Tech suspension, Takasago rims, Gorr cylinder, DLS brakes..

Still ironing out the bugs.. just been talking to Matt Wiley at Race Tech. Forks are great initially but get harsh.. we are dropping the oil level. Also just fitted a smaller back tire. 100/100/18.

Once i get the bugs ironed out, i hope to ring its neck.....

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