E: Engine Liner/muff clearance

Whatever you have as distortion in the cases, if it is not from welding - or if you intend to do some critical machining somewhere, all the throughbolts will easily clamp the job tight enough, alu flexes a lot, so no need for lengthy planing the mating faces.
The use of silk threading plus liquid seal on aircraft engine joints may simply show the ignorance of modern tech there plus the big problem of certification costs for any mods in aviation. This practice is best ignored here , just apply a good sealant. I like the anaerobic Loctite types that also do great load transfer across the joint. That is one of the reasons I do not use silicon here, argument is, a rubberlike medium in a certain thickness will hardly produce a rigid unit. So instead I´d point to the Loctite types like 573 , 574 , rubberlike anaerobic types also there, as required. These seals don´t shrink, no thinners , have strengths from very light to medium, so think before using. You cannot remove them easily, so some scraping, sanding is necessary, or use Loctite gasket remover or tough paint stripper overnight. Threebond is quite similar I believe, documentation is better with Loctite, shelflife no factor.

Vic

I agree but only to an extent..............When you live in a hot climate like I do here in Australia Time is a big factor in assembling engines or anything else of a similar nature when it comes to using sealants. Remember when assembling a twin that once you apply the sealant to one case half, not only do you have to align the bearings to get the crank right, you have many different length through studs to sort out ( I always sort this out before an engine assembly) the front prop stand assembly should be fitted at this point as well. And to top it off..........One thing I do, which many would not, is to apply sealant under the heads of many of the through bolts, as this is a big area for future oil leaks. Especially the ones in the lower rear primary area where this oil flows along the studs and drips off the bottom of the kick start cover/G 50 plate. If you use a sealant that dries once the air is removed and it hardens you will struggle to bolt the cases up properly before it goes off. This is where flexible sealants that do not set rigid hard or set quickly is very important. I guess everyone has their own methods, I don't like making the same mistakes twice.

My cases are bad where the gearbox was welded, The silicon has worked fine for many years, But I don't use it where it could get into the engine. Cheers Bill.

greg brillus said:

I agree but only to an extent..............When you live in a hot climate like I do here in Australia Time is a big factor in assembling engines or anything else of a similar nature when it comes to using sealants. Remember when assembling a twin that once you apply the sealant to one case half, not only do you have to align the bearings to get the crank right, you have many different length through studs to sort out ( I always sort this out before an engine assembly) the front prop stand assembly should be fitted at this point as well. And to top it off..........One thing I do, which many would not, is to apply sealant under the heads of many of the through bolts, as this is a big area for future oil leaks. Especially the ones in the lower rear primary area where this oil flows along the studs and drips off the bottom of the kick start cover/G 50 plate. If you use a sealant that dries once the air is removed and it hardens you will struggle to bolt the cases up properly before it goes off. This is where flexible sealants that do not set rigid hard or set quickly is very important. I guess everyone has their own methods, I don't like making the same mistakes twice.

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Why muck about with sealant. Just put an 8mm x 1mm O-ring under the head. that after lightly countersinking the hole.

clevtrev said:

Why muck about with sealant. Just put an 8mm x 1mm O-ring under the head. that after lightly countersinking the hole.

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OK trev as soon as I find a 5/16" X 3/32" O ring I will try that

Greg, thanks for pointing me to the trouble spot with the seven through bolts around the gearbox. I did think about fitting small o-rings somehow but did not like the reduced seat for the bolt heads or nuts that might get squashed under loads. So instead I will do as I did on a ohc twin Horex for the head bolts, turn a flat taper of around 3-5 degrees to the underside of the nut or bolt head. First use a countersink to get a reasonable flat recess in the case and the flat taper, as shown with a felt pen scetch in the photo, will form its oil tight seat in the softer alu perfectly. Just apply a little grease for the seat before torquing down the bolt.
Some Loctite anaerobic sealants should be slow enough for fitting the cases close enough starting where the biggest gap from distortion may be. Never had troubles so far with cases - but recently did have to hacksaw an aluminium clutch centre off an adapter that I intended to fix by Loctite 648 on a fine left hand thread - but was too slow to thread it on to the stop, one millimeter too short, no chance . . .

Vic

I'm not sure what the deal is with 648. I think they say you have 5 minutes, but perhaps very sensitive to temperature? 5 minutes seems rather optimistic to me. I've had it set up almost instantly... mid install and it's a soul sucking event. Maybe something like 640. Not really for threads, but you could stop mid install and take a nap.

What is critical about anaerobic types is the gap size, not just time. With minimum gap or light press fit it reacts within seconds. So it depends on conditions of use - and type of course.
In case of adapter-clutch center, last photo, I was going too slow, wanted a good full contact in all windings of the trread - but was way too slow as I had an activator applied as well because of a not so fresh pack of 648 and stainless steel/alu mating.

Vic

there are at least 2 through holes where "O" rings under the stud heads will not work..........Anyone guess which ones. Put some sealant on the threads of at least the lower four screws holding the gearbox cover on, or else you might find your gearbox oil slowly leaking into the primary area..............

oexing said:

What is critical about anaerobic types is the gap size, not just time. With minimum gap or light press fit it reacts within seconds. So it depends on conditions of use - and type of course.
In case of adapter-clutch center, last photo, I was going too slow, wanted a good full contact in all windings of the trread - but was way too slow as I had an activator applied as well because of a not so fresh pack of 648 and stainless steel/alu mating.

Vic

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I have used 680 and it goes off in a fraction of a second, very scary - so much so that I no longer use it - to many close shaves! Reading the tech info 640 seems the way to go, its said to be slow curing and is what I will use when next needed