head gasket

[mickwinf]

very depressed today, bike was a bit reuctant to start and seemed to be backfiring if i opened the throttle quickly so suspected carbs but on close inspection it is the head gasket, i can feel the air being forced out just below the carbs and there is some oil leaking. I have rebuilt the top end with new gaskets, cleaned everything thoroughly and torqued down correctly using brand new genuine honda nuts and washers. The ony thing is i used a pattern head gasket off Ebay. What is the thinking on this, would i be better off using genuine gasket?

[hairygit]

Always best to use genuine Honda gaskets, engine rebuilds are tedious and time consuming , and it's infuriating when a pattern gasket leaks At least you can change it with the engine in the frame, unlike us 750 owners

[Bryanj]

Never had that problem with any gasket mate, and i've rebuilt too many to count--very few with genuine gaskets!!.

It would suggest that something is stopping the head going all the way down, or its really badly warped---which i also have never seen---or possibly damaged--which i have seen

[matthewmosse]

Only gaskett leaks I've seen are on my 'keep it running another week' rebuilds where I reused a head gaskett - engine was a rough lump anyway with a dropped valve having chewed up no 1 cylinder head surface. Still ran ok like that for several years before the camshaft snapped. Ran fine for those 2 years, leaked oil from the head gaskett etc but power and startup fine even with the fickle 550k3 carbs. I'd double check that the air leak isn't out of either the inlet or exhast areas using a washing up liquid / water mix applied liberally. Only other thing I'd suspect at all likely might be a naughty ebayer selling a used head gaskett as new. Sometimes they do come out looking really clean, and I've bought 'new' gasket sets off ebay before now where the parcell has included one or more pre used bits amoungst the left over sets (where someone only ended up using say the cluch set of gasketts or whatever) Ive only ever had one problem with pattern gasketts, where an o ring was for some reason too thick and once bolted together it deformed and blocked the top end oilway causing the dropped valve I mentioned earlyer. I now always turn the engine over on the kickstarter with the rocker cover off to see the oil actually flush the oilways before fitting a camshaft.

[mickwinf]

ah well i will have to take off the head again but dont know when i will get time as i am moving house and bike is locked in a storage unit with the rest of my worldly possessions! Bryan what could possibly be stopping the head from snugging down properly, now i think back it did seem to take a bit of persuading into position !

[matthewmosse]

Not any chance one or more of the studs has partially unwound in the bottom cases? then the nut might not go past the threaded portion. other part that can snag is the camchain tensioner which needs to seat properly in the bottom crankcase, likewise the guide blade needs to seat properly at to and bottom.

[Bryanj]

Incorrect locating dowels possibly, i know that has happened on 750's

[mickwinf]

thanks will check all the above

[mickwinf]

well i got another head gasket (genuine) so thought i would take head off to replace it. before i unscrewed the head nuts i thought i would recheck the tightness, and they were loose! I think something had stopped the head seating properly (as suggested by Bryan) but after running for a while it must have settled down to its correct place thus loosening the nuts slightly. So i took a chance and torqued it down, result! Sweet! Then had to replace a duff plug to get it running on 4, but very happy!

[matthewmosse]

That's a good result.

[Bryanj]

Lucky you havent blown a piece out of the gasket or dislodged the "O" rings, keep a good eye on it for a while and make sure plenty of oil is reaching the cam on both sides.

[mickwinf]

will do Bryan, cheers