Author Topic: B31 leaking head bolts  (Read 222 times)

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baza57

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B31 leaking head bolts
« on: 28 September, 2020, 11:51:58 »
I have just re-built the engine of my B31 but cannot stop oil from running down head bolts, it does not smoke at all when running just leaks down all 4 bolts, any ideas? My 37 empire star has the same bolts but they do not leak.

Jim S

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Re: B31 leaking head bolts
« Reply #1 on: 28 September, 2020, 13:20:46 »
I had this problem on my 1949 B33. In my case there were 2 potential causes.

The cup washer that one of the valve springs sits in was partially blocking the oil drain hole for the rocker cavity. It could cause excessive oil accumulation in the cavity which could migrate down the valve stems into the combustion area. This was addressed by drilling a champher on the drain hole.

The other potential cause was a poorly reamed hole in the head for the exhaust valve guide. Oil was flowing down between the valve guide and the head. The machine shop bored an oversize hole in the head and installed a new guide with a viton seal.

After these improvements were made the engine is surprisingly dry.



baza57

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Re: B31 leaking head bolts
« Reply #2 on: 28 September, 2020, 17:02:38 »
Sounds plausible but surely it would smoke, this does not smoke at all?

idie

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Re: B31 leaking head bolts
« Reply #3 on: 28 September, 2020, 17:39:42 »
You say oil is running done the head bolts does it happen when riding. It could be that you have a bad seal on the push rod tunnel. The rubber seal at the top and under the castellated nut. The oil can leak from there and get blown back onto the fins and then run down the bolts. This happened to my B33.

baza57

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Re: B31 leaking head bolts
« Reply #4 on: 28 September, 2020, 17:48:15 »
Its bone dry round the castellated nut and no oil on the fins there.

Jim S

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Re: B31 leaking head bolts
« Reply #5 on: 28 September, 2020, 18:02:58 »
I wasn't getting much visable smoke either, but the inside of the tail pipe was oily soot. Also the spark plug was very sooty.

Have you checked the rocker oil feed and drain lines for leaks?

Check around your barrel. If the oil is starting just below the head/barrel joint, it is coming from the combustion area. Also, the same oil gets blown back on the carburetor, dynamo, magnito, battery making a sooty mess of the area. On every ride I was getting a little river of oil running down the crankcase just below the forward left head bolt making me think that the oil was coming from the barrel to crankcase joint, or the bottom of the head bolt inside the crank. But not in my case. It was running down the head bolts from top to bottom.


baza57

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Re: B31 leaking head bolts
« Reply #6 on: 28 September, 2020, 18:31:41 »
Tail pipe is pretty good as is plug, it looks to be running down from combustion chamber, yet i lapped head to barrel with coarse and fine grinding paste, and all the bolts are tight as a drum and compression test is 140 psi.

Jim S

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Re: B31 leaking head bolts
« Reply #7 on: 29 September, 2020, 01:40:00 »
I can't contribute much more. My B33 engine ran like a train but leaked oil. Post valve guide fix it runs like a train and doesn't leak. (Much  ;).

Let us know what you find is the cause.

baza57

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Re: B31 leaking head bolts
« Reply #8 on: 29 September, 2020, 08:04:00 »
Will do another test run today, then take the head off and check those oil drains :-[

baza57

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Re: B31 leaking head bolts
« Reply #9 on: 04 October, 2020, 10:43:06 »
Found the cause of the problem.....whoever rebored it to +40 thou supplied a +40 piston with +20 rings!!! Had a job finding a set of +40 rings most suppliers saying unobtainable, but after 6 hrs of phone calls and working the buttons found a ring manufacturer in Yeovil, Cox and Turner. rings now fitted and no more leaks!

EDDIE SIMPSON

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Re: B31 leaking head bolts
« Reply #10 on: 04 October, 2020, 13:12:02 »
baza, tell me more about the ring manufacturer. all us b31 owners may need to go there sometime in the future.

baza57

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Re: B31 leaking head bolts
« Reply #11 on: 05 October, 2020, 22:50:33 »
The ring manufacturers are Cox and Turner, Huish Farm, Yeovil rd, Tintinhull, Yeovil, Somerset, BA22 8QL or ring Ian Cox on 01935 826816.
 For rings only ring Kit on 07377 366214. very helpful lot.....not cheap but at least they can supply. Also do re-bores, crank grinding, crack testing,line boring etc.