Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board Rebuilt A65 breather oil leak

Hi Guys,

I would be grateful for any advice on my newly rebuilt A65 engine (by SRM UK)

Engine starts and runs smoothly with exception of an annoying leak which looks to be coming from the timed breather up under the engine sprocket. (very difficult to see up.

This only happens when the engine is running and is not gearbox oil (no hypoid smell) or chaincase oil. (no level drop in chaincase SAE 20 after 150 miles) Over a period of 150 or so miles running on the engine oil level in the tank has dropped by circa 5/6mm.

I dont think wet sumping as oil level does not drop over a stored period of 2 weeks and it does not smoke on start up.

Any insights as to possible causes would be welcome however I suspect it is an engine out and strip job to fix if breather parts incorrectly fitted or damaged.

Thanks,

Peter C.

No, its still being run in, get the rings fully bedded in before thinking of taking the engine apart. You need to get some pressure behind the rings so the odd taste of full throttle for a few secs at decent revs will help achieve that.

It’s probable that the rings are still bedding in or not bedded in causing excess blowby. Does the oil smell of fuel at all? (This would be excess blowby if you can).

Did you use the GPM pistons which SRM sell? I found the pistons are fine but the rings are crap, after 500 miles the rings on mine hadn’t bedded in at all. I ended up fitting JE pistons from Ed V and never had another issue. Though some Hastings rings or some of the quality rings that MAP sell would be a less expensive cure.

Get the engine warm and perform a leak down test, a compression test would give you an idea, but a leak down test would be better.

The alternator wires have a grommet that can leak, you do not need much to leak to put drops on the ground. Those wires come through near the breather and are easy to check taking the peg and cover off. Inspect the sealing grommet.

Hi

As Kommando said, the rings are likely still bedding in. Leave things alone until you're sure the engine is fully bedding in before doing anything.
When you say SRM rebuilt the engine, you didn't say if it is still 650 or 750 with the SRM kit? Allan was referring to the piston type SRM sell for their 750 kits. I have used these pistons and rings with my big-bore kits and they have worked fine.
As Mark said the alternator wire grommet can be a cause a leak, once you've got it run-in, pop the primary cover and see if you can clean any oil off the wires, grommet and tube, then inject some silicone into the tube and build back and see if that changes your leak.
Should you have a 750 kit, then you will probably have had a rocker cover breather installed, I would have thought SRM would have blanked off the timed breather when doing the rebuild, which is something I do, just to prevent it leaking oil.

My tuppence worth

John

Thanks for the feedback. It is a std 650 cc with liners fitted by SRM.

I will monitor dripping as I run it in.

Only other thing that may be contributing is that I fitted a car type in line oil filer kit in the return. Would this impact the scavenging ability?

Thanks again,

Peter C.

No, the return side of the pump has double the capacity of the feedside and the back pressure from the filter is negligible. Only once come across it being an issue and the pump was on its last legs and that was the problem not the filter. Owner was an engineering manager and we made sure by reminding him of this self inflicted error as often as possible, as he rebuilt it.

Thanks Commando. Engine rebuild included a new SRM pumpl so no concerns there. I will put more miles on it plus check the oil volume in the sump then contact SRM for advice.
Thanks
Peter C