650 crankcase joint...

[rayswadling]

Having now got the crank back from T&L, I can start planning the engine rebuild.
I've looked through old posts about using a thin gasket all round the crankcase joint and want to go this route to reduce the chance of oil leaks from the joint.

My question is do I still need to use a gasket compound (Wellseal, etc.) with this arrangement? I know a lot of gaskets in modern cars and bikes are just fitted dry.
I suppose it depends on what material is used?

[chasdev]

I've not built my G9 engine (yet) but I have built dozens of later style alloy motorcycle engines, none of which use case-half paper gaskets.
Modern case-half sealers such as offered by Suzuki and Honda are more than capable of sealing any non-pressurized oil source and more or less permanently.
In addition, the sealers mentioned clean off easily with mineral spirits and as someone who has spent countless hours scrubbing stubborn dried case-sealer glue that's a big plus.Edited by - chasdev on 11 Jan 2011 5:09:10 PM

[Don Madden]

AMC twins are unique to my knowledge by having high pressure oil across the joint at the filter tunnel & the gallery feeding the top end so what works with other engines may not with ours. The thin gasket around the oil filter cavity is very important & I also use the "Rolls Royce" method of a thin thread all around the case joint imbedded in modern Three Bond sealant, which does not harden. From what I've read, the original Wellseal is just as good but is not available here. Cheers, Don.

[Groily]

I've used a very light smear on my 500s to good effect Ray. No leaks, anyway, and of course no need for the little standard gasket round the oil filter chamber.
The late and much-missed Biscuit recommended making the joints from Hallite for best results, I just use thin Flexoil gasket paper. A fiddly cutting and sticking exercise.
Whether the jointing compound is necessary or not I couldn't say, but it would have been a pain to find it was, having assembled everything without! And it does help keep things stuck squarely where you want them (ie right on the joint and not across an oil feed hole or something) as you grapple with the crankcase halves, trying to get the cams and follower pins to go smoothly home and the followers not to get in a tangle. Which they so love doing, even with the whole thing upside down.
So I'm in the smear of Wellseal (or whatever) camp myself.

[rayswadling]

What about the centre web itself? The copy of the workshop manual I have isn't very clear if anything is needed between the web and the crankcase half? As this also has oil under pressure I would expect to use Wellseal again?

This is actually one of the things I'm enjoying about working on these bikes again...The whole idea of doing things like making my own gaskets. Used to do this all the time when I had these bikes first time round...

[Eric]

You don't need anything to seal the centre web, but you do have to make sure you have it aligned correctly.

Its a bit complex see if your manual describes the procedure, otherwise search the forums it has been discussed before if this fails come back and ask and I will see if I can remember.

It involves fitting the web with fixings just nipped checking for rotation and adjusting, than fitting the other crankcase half and checking again, that sort of thing.

[Groily]

I've never used anything behind the web, but as Eric says, there's more fettling needed here. The thing is to ensure smooth rotation of the crank when the 2nd half of the case is put on. It will turn pretty easily with one outer main and the shells, but not always with both halves assembled.
Ergo the thing is not do up the centre web tight, put the crankcases together (no jointing compound etc at this stage), do up several of the fasteners and see if the crank turns as freely on three bearings as it did on two. It should self-centre if the web can move a tiny bit. Then disassemble the halves, not disturbing anything (in fact this can all be done without the cam followers etc mounted) and tighten the 6 nuts for the web. Etc. I have gone through this several times before now until happy!
The next question will be sidefloat at the centre main and if you find a source of variable thickness thrust washers pls tell us!

[wilko]

What about the the machined groove for an O ring trick? A friend of mine who has run a 500 twin for 10 years finally started spewing out between the cases and has pulled it down to do this trick!

[Groily]

nice one wilko! Dunno, not done that. Although I've had really horrible dynamo leaks and occasional cylinder base joint leaks, I've never (touch wood) had a leak at the crankcase joint with an all-round gasket in place. Now that maybe in part because I always run the twins on 20/50, but I'd be the last person to open an oil thread!

[1608]

These crank cases were not designed to have a gasket. Provided that you have checked that there are no high points or obvious gouges on the mating faces a good sealant such as the recommended 'Wellseal' will do the job. In the past if ever there was a hint of a leak the 'home mechanic' would simply over tighten things which caused distortion and hence the old cry of British bikes leak oil etc. etc. I have never suffered ( I know I'm sticking my neck out here) leaky alloy mating faces on my many bike engines over the years. The secret is to either flat the surfaces on a suitable flat bed or plate glass, and or run a fine file over any high points such as around bolt holes. These crank cases are not under great internal oil or air preasure ( except the filter tunnel ) providing that the crank case breather is working correctly. To sumerise, providing that the relevant mating faces are clean, even and squarely matched they should not leak. I even use a thin paper gasket with a little Wellseal on the dynamo to timing case joint with no leak. The secret is not to over tighten. I confess to one slight leak, and that is from the oil distributor housing nut which has a copper gasket and there is a lot of oil preasure at this point.
Just a final point, if you do try and fit a gasket btn the c/case halves, its can be a finnicky job and theres a chance that the gasket will tear or get creased and you won't know till you fill it with oil and start it up. Then you will see an oil slick!Edited by - 1608 on 11 Jan 2011 11:42:42 PM