Author Topic: Oil on piston crowns  (Read 269 times)

Online Minto

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Oil on piston crowns
« on: 01.03. 2021 18:34 »
Evening all,
I started stripping the plunger engine yesterday ready for removal for another rebuild to try to sort out some oil leaks. After I removed the head I observed that there was oil on top of both pistons, about a 1/4 -1/2 TSP on each at a guess, there was also quite a lot of oil on the top cylinder fin behind the pushrod tunnel. I took a closer look at the head gasket and there was also oil on the corresponding area of the gasket.
I'll try to do a leak test on the cylinder head and valves, but is it possible that this is all just a head gasket leak from it not sealing well enough around the pushrod tunnel?
Thanks in advance oh wise and enlightened ones.
Jason

There are a catalogue of other issues but I'll get to those as and when I get to them.
52 A10 plunger
Aprilia RSVR

Offline RDfella

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Re: Oil on piston crowns
« Reply #1 on: 01.03. 2021 19:16 »
Sounds like oil from dis-assembly. Oil won't leak into cylinders from pushrod tunnel - pressure in cylinders is somewhat higher than pressure in that tunnel so any flow would be the other way - witnessed by a black scorch mark on the cyl head gasket..
'49 B31, '49 M21, '53 DOT, '58 Flash, '00 Firestorm, Weslake sprint bike.

Online Minto

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Re: Oil on piston crowns
« Reply #2 on: 02.03. 2021 00:42 »
Thanks for the wisdom RD, there has been oil around the head and barrel join before disassembly so definitely a leak from there. Hopefully the oil on the piston tops is just disassembly spillage.
I'll take a closer look at everything over the next day or so between work.
Cheers
Jase
52 A10 plunger
Aprilia RSVR

Offline Swarfcut

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Re: Oil on piston crowns
« Reply #3 on: 02.03. 2021 14:26 »
Jase. While you're there check the two drain holes in the head and block at the front of the engine, and check again with the gasket in place but not tightened down. Any restriction here offers the possibility of oil pooling around the exhaust guides and in extreme cases being drawn down the guide.

 Swarfy.

Online Minto

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Re: Oil on piston crowns
« Reply #4 on: 03.03. 2021 02:13 »
Cheers Swarfy, I'll definitely give them a thorough looking at, that sounds like a distinct possibility.
Jase
52 A10 plunger
Aprilia RSVR