revtothelimit - motorbike forum

JackyJoll wrote: Sun Jun 27, 2021 9:32 pm You can make or buy a rocker cover gasket with individual pushrod holes, to align the pushrods with the rockers, as you fit the cover.

Yeah I saw those - I kinda wonder what happens to any bit of gasket which fall off in the PRT though! Why would they fall off I suppose.

JackyJoll wrote: Sun Jun 27, 2021 9:35 pm

Mr Dazzle wrote:the pressure above the pistons is an order of magnitude higher than that below it

A damn site more than an order of magnitude during combustion.

Yeah true - typically peak "BMEP", the average 'useful' press in an engine over the whole time it's running, is about 10 bar (probably a bit less in this bike). So if you just average the pressure in the cylinder over a long time including all intake, combustion etc. it's about 10 atmospheres. Or the pressure above the piston is about 10 times that below.

Peak pressure is more like 50-100 bar.

Annealing the head gasket in my kitchen...



I have read all sorts of conflicting advice on whether or not I should quench it (I.e. throw it in a bucket of water) or just let it cool naturally.

After some googling of forums I decided to do the sensible thing I should have done from the start and ask the materials department at work.

It doesn't matter! The copper doesn't undergo a phase transition on cool down so it makes no odds. They just suggested quenching cause you'd get a thinner oxide layer on the surface. So that's what I did.

I thought you only annealed used ones so you could reuse them, that looks brand new?

Yeah it was, but you never know. Could just be stamped out of a sheet of A N Other copper, almost certainly is from looking at it in fact, so who knows? I.e. it could just be a random copper stamping firm not a seal manufacturer.

It's definitely bendier now

Even new ones are usually harder until you anneal. You can feel it.

Dropping it in cold water cleans it and rules out subsequent burnt hands.

JackyJoll wrote: Tue Jun 29, 2021 8:45 pm
Dropping it in cold water cleans it and rules out subsequent burnt hands.

Yeah there's something deeply satisfying about how all the black just shatters off when you drop it.

Two cats in two toilets. Or is that four cats in two toilets? This is the third time I've tried to assemble box number 2. Got it in 5 mins this time. Clearly there's a knack, I just don't know what it is...



One cylinder head on one cylinder block. The bolts are just finger tight at the mo. Those really long ones go through the rocker boxes. I double checked the seal crushes and gave all the o rings a dose of silicone...slid together beautifully.

JackyJoll wrote: Sun Jun 27, 2021 9:32 pm You can make or buy a rocker cover gasket with individual pushrod holes, to align the pushrods with the rockers, as you fit the cover.

Turns out I'd inadvertently bought those anyway

Bugger!



I reckon the exhaust rocker box is bent. It was way harder to get lined up and on than the intake side. Tightening the bolts, even in stages, resulted in that ^^^^^.

So after thinking about welding and chemical metal and stuff I suddenly remembered I can just bond it back together! We've got some fancy pants epoxies and big ovens at work. Said adhesives need to be cured at sorta 100-150C, but the head is designed to get hot anyway.

That little lug doesn't bear much load so it should be fine. Might need some liquid gasket when it goes back together though cause I'm unlikely to get it dead flat.

I would just leave it out but there's a bloody great hole if you do. Not that oil tight

Oh and I also realised today that I forgot to put the little oil sealing bolt back on the exhaust tappet block. You can put it back in situ, thats not the problem.

The problem is that I've been turning the engine over to get the cams in the right place and make sure the push rods and still engaged and moving as I reassemble the rocker boxes.

Turning the engine over makes the oil pump turn over....

Well at least I know my tappets are getting oil now! Downside is the puddle on my floor. I also confirmed by a similar route that the rocker feed lines still have good oil pressure.

Going to be impossible to get your gasket face flat if you just epoxy them back together,you need to create a small gap for the epoxy to fill up, good luck.

Struggling to see how that happened - did you have the pushrods level with each other and the tappet adjusters fully slackened off?

The 'middle' stud on the box is either on the piss or more likely the box itself is twisted. I remember now it was difficult to get it off. I had to gently tap it upwards on the studs with a tiny hammer.

Both pushrods were down (I quintuple checked ) and the adjusters are right off.

The other box just drops straight on.

It wasn't sliding straight on but it was going on. It drops down flush at the inboard side and to within about 1-2mm of on at the port side. Then i was trying to pull it the rest of the way by tightening the 7 bolts in sequence a tiny bit at a tine. I figured that since it was like that for years before it would go back on.....Fell foul of the classic problem, what feels gentle on the spanner is actually putting loads of force into it.

It goes on dead smooth now, with that middle stud missing!

Le_Fromage_Grande wrote: Fri Jul 02, 2021 4:56 pm Going to be impossible to get your gasket face flat if you just epoxy them back together,you need to create a small gap for the epoxy to fill up, good luck.

Yeah absolutely. I will almost certainly use something with 0.1mm glass microspheres premixed in. That way when you clamp it up tight you get the 0.1mm bond gap you need. Hence the comment about gasket goop. The problem comes with making sure the stuck on bit doesn't hold everything else off. It needs to be subflush.

Fortunately the broken off piece fits perfectly back into the space. You can see it sticks up slightly though, probably about 0.1mm.



Had a brief chat with the materials guys at work, it might be better to use a cynoacrylate - superglue basically - rather than epoxy. They're gonna review their datasheets.

If the base of the box isn’t flat, you’ll see it when you put the box on a sheet of glass.

That bit breaking off is a new one on me!

So the official advice from the materials guy is to use an anaerobic retaining compound, e.g. loctite. Bonding will be difficult 'cause you can't really prep the surfaces that well, certain loctites will be good for that 'cause they'll stick to inactive surfaces.

Epoxy will struggle with temperature potentially, the cylinder head gets pretty hot. Not sure how hot exactly 'cause it's air cooled, but water sizzles off it so it's gonna be well above 100°C.

We have some high temperature Silicones too, but they need to 'outgas' during cure so they're not ideal for bonds that are sealed up.

Loctite 638 actually looks OK, it retains strength even when submerged in oil at 125°C and cures in a sealed space. It also means I don't need to bake the cylinder head to stick it.

Is there enough metal and access for it to be pinned once glued back on?

Is there a metallic version of woodworker's biscuits?

I think it’s going to end up welded.

JackyJoll wrote: Mon Jul 05, 2021 2:34 pm I think it’s going to end up welded.

It'll save Daz fixing it more than once. Do it right man.

It's not really loaded that much...the only thing it has to do is hold oil in to a large extent. The boxes are bolted down on the other side with the main head bolts. I think these little bolts are more about getting the oil seal on the gasket, which I may have to address with goo. All I want it to do is not leak, or at least not leak any more than the rest of this sieve

I've been looking, a new reconditioned head is only a few hundred quid (I paid £700 to get this one welded, reassembled with new springs, guides and valves plus a cylinder re-bore). If worst comes to worst I can take the lovely new springs and valves out of this head and put them in another one. It's not even the original head on here at the moment anyway.

P.S. the materials guy did say "just bloody weld it, I fucking hate glue!".

P.P.S. the other thing to consider with welding it that it'd be bloody hard to get that gasket face flat again. In fact it's already been welded once on the exhaust side to repair to ovalised guide hole, so maybe that contributed to it being distorted in the first place. Who knows. I think if bonding doesn't work I'll just get a new head.

Cant you weld it so its ever so slightly proud then get it skimmed to original height, iyswim?