Rubber rocker cover gasket leaking

[MGST]

My Honda ( 250cc single ) has got a rubber rocker cover gasket. It leaked ( "breathed" is probably more like it ) a small amount from everywhere when I got the bike 2 years ago. I rebuilt the engine 15 months ago and used a full set of brand new genuine Honda gaskets. There is a channel in the rocker cover for the gasket to sit it, and where the gasket sits against the head is flat. I made sure there were no burrs on the head, that all the surfaces were clean and oil-free, everything was sitting nicely, torqued it up to spec etc. It has always "breathed" a little cos one of the rocker cover securing nuts has a stripped thread ( a back one ). After 3 rides during the hols ( = sustained high engine speed and thin oil cos its hot for a long time ), it is really pissing oil out the front of the gasket now, which gets blown back and covers the whole bike and me in oil. Surpose it's one way to stop it rusting?

Anyway, I pulled the rocker cover off tonight and removed the top half of the cam bearing holder cos that has the stripped thread in it for the cover. I will take it to work tomorrow and heli-coil it. But I can't see how that will stop the oil leaking out the front cos that screw is at the back and both the front screws are fine. Anyone got any ideas? I always thought you didn't have to use gasket sealant on rubber gaskets?

[xwhatsit]

Order a new gasket from Econohonda (http://www.econohonda.co.nz). They seem to thin out eventually. Can't be too expensive, useful to start from scratch at least.

I know with the 250RS/XL250S motor (which is the previous version of your motor) which were made with plain bearings in the head for the camshaft, the head and the rocker cover were made together as a one piece unit. Try mixing and matching rocker covers and almost always there were little imperfections and differences in the machining which would cause oil leaks from there. I got around it with lots of sealant but it still weeps. Cylinder head/rocker cover been swapped at some point?

You absolutely 100% certain that's where it's coming from? I've spent a lot of time tracing oil leaks and one thing that's constant is you get tricked where they're coming from. You sound like you know more than me about engineering, but I'll offer the advice to grab a can of degreaser and see if you can be sure that it is coming from the rocker cover/cylinder head join.

[MGST]

I got all the parts from Econo originaly. The original gasket looked ok, but I thought what the hell, its easier to put a new one on now while I've got it in bits. Famous last words aye? Don't fix wot ain't broke.

I degreased the whole bike after the previous ride ( 3 JAN ), and never used it again until this ride ( 12 JAN ), and the oil seems to be coming from the top of the engine and running down. The first part to show signs of oil is the top of the head immediately under the gasket.

My motor is the MC10E, single cylinder DOHC, same as CBX250RS(E). The barrel has been replaced at one time ( from a CBX250RS cos the barrel is painted black, mine should be plain alloy finish ) but everything else *looks* original. If the head and rocker cover on the CB250RS was one piece, how can it be mixed and matched with mine ( separate )? Sorry don't quite understand, probably misread you.

[xwhatsit]

No, sorry just outlining a common problem with the 250RS. They were made as a matched pair (separate though, just like yours), and if you pinched a rocker cover off another 250RS then you'd have hell trying to stop top-end leaks. If the barrel was replaced on your bike, perhaps either a new cylinder head was used (and the old rocker cover kept) or vice versa -- meaning that they didn't quite match together as there were differences in machining (not a matched pair). All bits from the same model though of course, just from a different GB250. But then again there's a rubber gasket so it shouldn't be an issue really.

Bit of silicone can't hurt, especially as you have a cam bearing holder-thingie, so tolerances between cylinder head and rocker cover aren't quite so super-important.

Be interested to see what happens once that thread is helicoiled. It might be an oil-feeding bolt (on the 250RS motor certain threads in the cylinder head have oil pumped through beside them or something) -- does it have a washer on top? Is it supposed to in the book? I know it's at the back, but these things are deceiving

Good luck, I love those bikes.

[MGST]

No, sorry just outlining a common problem with the 250RS. They were made as a matched pair (separate though, just like yours), and if you pinched a rocker cover off another 250RS then you'd have hell trying to stop top-end leaks. If the barrel was replaced on your bike, perhaps either a new cylinder head was used (and the old rocker cover kept) or vice versa -- meaning that they didn't quite match together as there were differences in machining (not a matched pair). All bits from the same model though of course, just from a different GB250. But then again there's a rubber gasket so it shouldn't be an issue really.

That's what I thought.

Be interested to see what happens once that thread is helicoiled. It might be an oil-feeding bolt (on the 250RS motor certain threads in the cylinder head have oil pumped through beside them or something) -- does it have a washer on top? Is it supposed to in the book? I know it's at the back, but these things are deceiving

No its just an ordinary solid bolt, only for holding the rocker cover on. There are other banjo bolts in / on the motor though.

Good luck, I love those bikes.

They're pretty rare here. I have seen one other in person, and 2 on Trademe, but none of them had the single seat cover like I've got, only the pillion seat, which I've also got. It will be for sale after May when I get my full licence.

[awayatc]

at work we have rubber in various diameters on a roll, which you cut to size and glue together to make your own oilseals....Nor sure who would sell that here Schuck maybe? That way you can go a bit fatter, which would help.
I have also used treebond in the past on various rockercover seals, just put in a bead in the groove. (With subarus it pays to add a washer so the bolts dont bottom out....)
Good luck