2 head gaskets in two weeks

[britshgigolo]

fitted the new reboard cylinder with what i thught was an original gastek but but was not 100% sure lasted 40 miles and overheated blown coolant out so striped it all down could not see anything wrong so ordered an original gasket from yamaha turned up and fitted couple days later all been fine for week and bit and tonight on way home it was getting warm again pulled over and check and coolant had droped so pulled over and let it cool down and got bottle of water from a shop toped up with half a cup as not a lot was lost and made it home check again when i got home and was low again first time was pumping back to bottle and overflowing but this time its not but it blew the power valve cap off to after letting it cool down now not sure what to do head had squish band done by mick i checked and lightly skimmed the cylinder and all seemed good and straight now thinking it may be a doggy head as dont make sense but then why second time round lasted week and bit before going again whats people thoughts just bad luck or missing somthing

[gareth_iowc]

Thermostat stuck closed?

[Calum]

This!

Check the thermostat

[britshgigolo]

must admit used the thermostate that came with the second hand cylinder and head would that cause the head gasket to blow as im seeing oil in the water when topping up plus got oil leaking from around the plug so asume water getting in the head

[Calum]

@britshgigolo If the bike overheated then yeah.

As said I always like to give the barrel and head a light skim.

[britshgigolo]

I did skim the barrel but not the head as Mick did the Squish band and said he had to heavily skim it to get it right so thought it would of been ok but will strip it down again in next couple of days see if I can see anything thank

[NINJA]

The small extra cost of some quality gaskets is always worth it in the long run for-sure!!! ;0

[britshgigolo]

Well as last gasket was a genuine Yamaha what's people thought on a copper gasket as been told it could be worth a try just not sure on best route to take now will get it striped back down and see if can tell what's going on I know it got to be something silly I'm doing wrong as it nothing major the head was all torqued down before going in and rechecked after two heat cycles

[britshgigolo]

I forgot to mention it blew the power valve cap off the second time after letting it cool down and top up with water don't know if that's a sign of something

[Calum]

Powervalve cap? Wtf that is bolted on.

[britshgigolo]

@Calum yes I know striped the threads don't know if they were doggy to start with so re tapped to next size up and now I know they good just thought I would mention incase it meant something

[Calum]

@britshgigolo Yeah well there is going to be massive pressure there bud, you will be massively down on power as well!

This would have nothing to do with the head gasket though mate. This has to do with the fact two strokes are designed to create a pressure wave to lost fuel and air back into the combustion chamber.

[andrewj1680]

Mick did my cylinder and head the other week and didn't skim any of the faces he ported it and did the squish but am guessing he didn't feel the need to skim them I cleaned them up torqued it down with genuine gaskets and tbf the bike hasn't missed a beat but then there was nothing wrong with it before I stripped it for Mick and the bikes done less than 5000 miles

[britshgigolo]

yer when he did mine he skimmed the head heavly to get it right and told me to use two spark plug washers/gaskets to be on the safe side to stop the piston hitting the head wish i had sent the cylinder to him now but the idea was to get it done quick as was a spare top end so i could send my original off to him for him to play with and work some magic on but as have had problems im still waiting to get it running right before i send it off have ordered a new gasket and will skim both head and cylinder again and see what the out come is as no rush as have put the original back in for now as use for work eveyday

[andrewj1680]

@britshgigolo I had mine back within a week bud definitely worth having down it responds better on the throttle at whatever rpm where as it really felt lazy before

[britshgigolo]

thanks for the info and yer will be getting it done as soon as the other runs fine there no point with the spare as its on max limit now so will be getting it resleaved then will send that off to as always good to keep spare on the shelf as never know

[britshgigolo]

Well think I found the problem the piston was catching the head gasket it has been bored to its limit so should of checked really but hope now it will be all ok give the bore and head a light skim to make sure it had not warped but all seems ok so fingers crossed this time will go ok when I get time to put it back in

[Calum]

If the piston has been bored to it's limit then the powervalve is going to need modifying.

If you don't then I guarantee that the engine is going to seize again!

[britshgigolo]

i had already done the power valve before and that had no signs of problems when i took it apart just the head gasket and its where you can see it has blown across from the cylinder to the water jacket so hopfully this time it will all be ok

[Calum]

@britshgigolo You may find a copper head gasket will be your ticket, if modifying the gasket proves too difficult.

I believe you still need sealant on copper gaskets, although don't quote me on that.

Just be wary of the powervalve is all.