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Crankcase Joint-Prep and sealing

1660bob

Well Known and Active Forum Website User
VOC Member
Hi All, a Heads Up on this if you are putting a motor together: prepping my cases for joining together this week.Probing around with them bolted and nipped up in a dummy run, I saw that there was a clear gap in the casing joint allowing light through at the bottom of the crank chamber. On checking, I found that the cases were just marginally held apart by swellings in the alloy around the two lower crankcase dowels.Seems to me that rough handling when pulling the cases apart in the past has wrenched the dowels slightly, and pushed up the alloy around them,holding the cases from pulling up as they should.I also suspect that a little swelling occurs around the edges of the oil filter chamber cap if this is overtightened-(and lets face it-with a hexagon like that tightening onto a taper seat-easy to overdo it) Its so close to the joint at the rear of the cap that any distortion from excess tightening of the cap is directed right onto the joint line. I`ve flatted things off carefully, but its one to watch for when prepping.
I am going to use Threebond 1215 on the joint as its reckoned to be the best sealer and any 60 yr old cases need all the help they can get- anyone used this? comments please, Bob.
 

vibrac

Well Known and Active Forum Website User
VOC Member
I am a silk thread man seems to work for me Hylomar or other clever goo. using the thread seems to make the difference
 

riptragle1953

Well Known and Active Forum Website User
Non-VOC Member
I used to get rolls of fairly coarse sandpaper and tape it to a flat plate and use it to lap the high spots from mating edges.
 

nkt267

Well Known and Active Forum Website User
VOC Member
I saw the silk thread idea used on aero engines,seems like standard practice, not till i strip the engine again though.John
 

Paul Ennis

Well Known and Active Forum Website User
VOC Member
I used 3 bond on all joints, without gaskets, when I replaced the bigend last year. All joints are still bone dry, but, covers are difficult to remove; I think it's a little price to pay for an oil-tight engine.
Paul.
 

b'knighted

Well Known and Active Forum Website User
VOC Member
Hi Paul,

If you run a tap through a couple of the cover screw holes, and carry a suitably slightly larger screw in your tool box, the covers become almost self extracting. The Norton Interpol II uses this method to good effect, and has O rings under the screw heads, but as I have never cut Stevenage metal I can't bring myself to tap my covers.
 

Paul Ennis

Well Known and Active Forum Website User
VOC Member
Thanks Ian, that's an idea I use on my model traction engine, but I've never thought about using it on motorcycles, doh!
Paul.
 

nkt267

Well Known and Active Forum Website User
VOC Member
From what I remember using silk thread to assist sealing of engine joints.
Apply your prefered sealant and run a continuous length of silk thread all around the middle of the joint,bolt/screw holes as well,over lapping where the silk finishes and ends so that when you bolt the joint faces together the silk takes up all the minor gaps and gives a perfect seal.john
http://www.youtube.com/watch?v=vB0MIQVH9Mo
 
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