crank case leak

1957 Thunderbird... small leak in the crankcase seam between left and right halves. Is there anyway this can be cured externally or does it require the full job?

I suppose it depends whether is is a genuine leak or one caused by excessive lower crankcase pressure.
If it is the latter there are a number of ways to reduce pressure and maybe with it, stop the leak.
There are many threads on this site on crankcase ventilation
It's worth a try - unless your sure you have a dodgy joint, in which case it is probably a bigger job

It belongs to a friend and I haven't seen it yet. I mentioned possibly installing a crankcase vent but unsure of where to fit it. I am much more familiar with Nortons and unit Triumphs. Is there any way to access the back of the timing case with out drilling the existing case? I know units have the breather off the inlet cam but that is not enough.

It could be a leaking case joint, it could even be cracked cases. Either will require a full strip down to fix properly. But Triumphs have numerous other potential leak points that are far more likely IMHO...

You’ve got to clean the old oil away if you wanna find the source of the leak. Give it a proper clean down with Jizer / Gunk etc, get it running again and have a good look around it.

Crank case pressure is definitely a good thing to look at first. It’s very easy for someone to fit a solid cam, or similar, by mistake and block off the timed breather.

Then there’s the sump filter area, lots of gaskets and studs there to leak.

Pushrod tube seals are a place where many (most?) Triumphs leak, yes it’s a weak design but the real problem is Triumph subtly changed the design of tubes and seals et al over the years so most bikes today will have a mix n match collection of parts, and most people today do not know what’s right or wrong.

Base gaskets and rocker box gaskets are other favourite leak points.

Any leak above the cases will obviously make its way down and can easily look like a crank case leak.

When he brings the bike to me I will clean it thoroughly and really try to spot the leak. The only way I can think of to install a breather is to drill a hole approx 1/2" diameter just under the distributor. Since it is a very nice Thunderbird I can see his reluctance to do this. But a breather is essential .
The dreaded pushrod tube section is a minefield like you said...years of mix and match.

Easiest way to put a breather on it would be to bodge a fitting into 1x inlet and 1x exhaust rocker box inspection caps. It’s not ideal, as the gasses have to come up through the tappet blocks, but it might work, especially if you put a reed valve in the breather hose.

I have just that problem with my 850 motor. When you have fixed your's, you can come and do mine. I've figured out that if I lift the whole motor out, I might be able to lift the barrels and get the case halves apart without disturbing the timing.

seattle##gs said:

1957 Thunderbird... small leak in the crankcase seam between left and right halves. Is there anyway this can be cured externally or does it require the full job?

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No idea of whether it's successful or not but I have read somewhere about aircraft engine oil leaks that are cured by a vacuum pump fitted to the engine,
Then solvent applied to clean the offending area .
Then lastly sealent applied and sucked into the joint saving an expensive strip down
No idea if this is ever done but I would really like to know

acotrel said:

I've figured out that if I lift the whole motor out, I might be able to lift the barrels and get the case halves apart without disturbing the timing.

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It ain't easy, but it is doable. You can also leave the pistons in the cylinders (as long as you don't tear the base gasket), and the head undisturbed from atop the cylinders (you do have to remove the rockerboxes to re-set the pushrods. I hope you don't drop a cam follower!