G12 engine

McBob · Post by **McBob** » Wed Apr 18, 2012 11:03 am

When my engine was rebuilt the cases to barrels were sealed by the method mentioned by Don. The cotton was cut to correct length and "tacked" in place with a tiny amount of super glue. What leaked before leaked no more!

cf160 · Post by **cf160** » Sat May 05, 2012 10:42 pm

Sounds like great advice! Thanks to all the experts who contributed .
Dave(cf160)

zwarts · Post by **zwarts** » Sun May 06, 2012 7:04 pm

Re. sealing the cylinder base/crankcase joints. I used to be plagued by oil leaks in this area and it was always difficult to see if the leaks were from the above faces or from the pressurised oil gallery between the two crankcase halves (from where the cam oiljets/rockers are fed). The cure is simple, but can only be applied when the engine is dismantled. First,clean out the threads in the cylinder stud holes (5/16"BSF, in the pre-6? engines, 3/8"BSF thereafter) with a 'bottoming tap'. Then countersink the top of each stud hole to remove any pulled up alloy. Finally, using fine grinding paste, lap the barrel and crankcase face together until there is full contact all the way round. Be very sure there really is FULL contact Thoroughly wash all traces of abrasive from the cases and barrels. I find I can refit the barrels with standard (thin) gaskets and just grease. The extra thick gaskets which are available are treating the symptom and not the cause, so avoid those). No sealant required, although Wellseal or Hylomar could be used, by disbelievers, for extra security against leaks. There is also a tendency for oil to 'wet' the base gaskets by finding its way up between the crankcase and the barrel spigot. I prevent this by fitting a BS 041 nitrile O ring at the 'top' of the spigot i.e. where the spigot meets the cylinder base. The cases already have a chamfer here which is big enough to accommodate the O ring. I use the same lapping technique on my single cylinder engines where it is equally effective.
Bob.

wilko · Post by **wilko** » Mon May 07, 2012 1:00 am

The O ring idea is a goodin"

rex.webb · Post by **rex.webb** » Mon May 07, 2012 9:11 am

My wife,s Needle work box had better look out ?.

Any one need Thread for Sealing ?
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