Sealing the ET109/xAS crankcase bolts

A_HRD

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I am shortly going to be putting my Wyatt Twin crankcases together for the last time having got the crank all shimmed-up nicely (and I even remembered to tape the little gear-change bevel-gear in place so I don't forget it!).

One of my pet hates is oil seeping from crankcase studs and through-bolts after a long hard run. I was considering machining an o-ring groove on the inside face of each nut (which is effectively the "bolt-head" on the ET109/xAS bolts); perhaps even on the securing nut at the other end too.

Thinking more widely, I had a look on ebay and there are loads of copper/aluminium/nylon/fibre crush-washers available that might suit the job in hand. Meanwhile, I was looking in my "box of useful bits that I probably won't ever need" when I found a handful of dowty seals which are a snug fit on the 5/16 "bolts". Now I really like the prospect of using those for the job… But before I do, I thought I would ask forum members what solutions they use to prevent oil seeping from crankcase studs/bolts over time?

Peter B
Bristol, UK.
 

greg brillus

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Way too much trouble............Just install them with a smear of threebond under the heads, in particular the ones from inside the timing chest and the primary chaincase ones. I smear some over the heads once I have pulled them up tight. Don't forget to plug the through hole for the kickstart shaft as well, even at that height, it still bleeds oil along itself. I've seen ground down red fiber washers used under the heads of the through bolts, but I didn't like that idea at all. Only one place for those washers on a Vincent, and that's on the carburetors.
 

chankly bore

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I would think that using a soft washer might cause more problems than it cures. The crankcases expand when hot and the studs do stretch. If something softer than a steel flat washer is in place, then that something will compress.When things cool, they will be looser. As a matter of interest, early Twins did have a soft washer ET187/1 under the magneto cowl tab only. This was because of the design of the through stud from the inner timing case wall. I'd suggest a little jointing compound under the head of any stud exposed to breathing pressure and oil and ditto at the nut end. Your nicely machined crankcase faces should cure everything else.Trev's idea is good. You only need a freep of a counterbore as the holes are already at 21/64" (most of them.)
 
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Albervin

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Like Greg I use Threebond under the heads of the bolts and a light smear on the threads. Very easy to work with and it stays flexible. After two years since the rebuild not a skerrick of oil has escaped.
 

Peter Holmes

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Like Greg I use Threebond under the heads of the bolts and a light smear on the threads. Very easy to work with and it stays flexible. After two years since the rebuild not a skerrick of oil has escaped.
Threebond have a large range of products, which actual product do you use?
 

greg brillus

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The two products I use are 1215 which is grey, and specified for use on the assembly of transmission cases, perfect for any alloy case/housing finish. I have assembled countless engines with it, and I use it all the time. For Shadows I use 1207B which is black and is able to withstand high temps up to 320 degrees Celsius which is good on exhaust joints as well, so perfect for a hot running air cooled engine. Both these types are Non-sag solventless silicones. As point of interest I used some of the 1207 B whilst assembling a set of freshly painted Shadow cases not more than 4 hours ago..............;). Easy to clean up, use plenty of clean rags, as the black stuff really is black............I mean really BLACK.............:eek:.
 
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