Fuether to: 1953 G9 'over-oiling'. Help please!

[craigcc]

Hi all,

I return to this topic after about a year, having given up trying to solve it in exasperation - despite acting on a very good range of advice and comments from members, all of which I acted upon. Thanks folks.

I've been using the bike (1953 G9) on and off over the last few months, gaily swanning around the village and local area doing steam engine impressions from the exhausts. I've not ridden far or too hard, as the head gaskets will blow (I think due to oil build up creating a high compression ratio). It runs very nicely and starts easily as one would expect from what is essentially a blueprint rebuild, with all engineering work done by T&L and every single wearable part replaced with new parts from reputable sources, mostly the spares scheme. Oil comes out of the exhausts in fair quantities, necessitating a good clean after each ride and my neighbours have invented various ribald nicknames for the bike.

Please refer to the original topic (in the title of this post) for the whole sorry story. The one thing that seems to be cured is the scavenge system (very strong flow back to the tank), though it does retain a larger amount in the cases than I'd like - something over half pint.

I'd like to get to the bottom of this.

So let's try approaching the issue differently:

My 1953 G9 (eng no 53/G9 14745) smokes badly and splatters a fair bit of oil from both exhausts. It has a history of blowing head gaskets. Discuss.

Refer to the other thread for what's been done already, but essentially, apart from the castings, crank, rods, timing pinions and (refurbished) oil pumps all other components are either brand new or are passive fittings which have been checked. (barrels on new +60 bore). Heads fit properly to the barrels.

All advice and comment appreciated.

Thanks!

Craig.

[aryden]

I had the same problem, that the cylinder head gasket has blown. My barrel is also +60 bore. The problem was that the new pistongs were to high, and hit the cylinder head. I had to rebiuld the cylinder head and barrel. I saw the marks at the pistongs and also in the cylinder head. The pistongs must be lower about 0,20 mm. The new pistongs +60 have another radius. I will propose that yuo take the cylinder heads of make this Control.
Regards Ã…ke

[duncansmith]

Daft idea... When did you last get your torque wrench checked? We get them calibrated every 2 years at work.
Also, which sort of head gasket are you using?

[clive]

Craig this over oiling is frustrating for you, but I am not sure starting a new thread is a good idea, you are likely to get all the same advice again. I was tempted, as a moderator, to move this into your old thread but instead spent the time to read it all through again, and was surprised to find that I had given some thoughts before.
Anyway having reviewed the previous thread I note that one entry suggested that engine, before a certain number, that were experiencing over oiling should have a washer mod fitted. Your response was you did not see how that could help. But it was manufacturers advice. So is your engine before that number?

If you have new valves and valve guides are you sure they are correctly manufactured?

Are you sure the heads are flat and that there is sufficient gap between lip and cylinder head to allow the gasket to be fully compressed. If the gasket shows any sign of oil leakage then I would suggest it is not being compressed properly.

Finally you seem to be convinced that all new parts are above suspicion, I doubt that.

And a thought, is your oil pressure relief valve working properly? From the sound of it, with short journeys you may not be getting the engine up to full running temperature. Using 20/50 instead of sae 50 would reduce the oil pressure at start up.

Good luck in tracking it down.

[craigcc]

Thanks Clive, much appreciated. Good of you to have another think about the issue. Comments noted repeat threads - will not do that in the future.

The valves and guides came from the spares scheme and seem OK, tolerances OK and the valves seal OK (did a leak test with solvent). I accept that new parts may not be above suspicion - indeed the metered flow valve alloy cylinder thingy that is driven by the exhaust cam was not made properly (got it from eBay) so replaced it with a spares scheme item.

The gap between lip and cylinder head is OK - I measured that, but I'm also beginning to wonder about the integrity of the heads themselves - they'd previously been gas flowed. All 'looks' OK, but I'm trying to source alternative heads to try them and see if there's a difference in the problem (can't seem to find it easy to obtain the correct 1953 heads - annoyingly, the others have slightly different stud spacings for head and barrel - why on earth did AMC vary them?

As far as I know the pressure relief valve is OK, paid close attention to that when I was having scavenge issues (which are still there, but nowhere near bad after all the work done on pumps etc). Not sure how to test the valve as such. Any thoughts?

But, I'll try your tip re 20/50 oil.

Until I can find alternative heads, I'm running it as is. Smoke is just about tolerable, though plenty of oil in the exhaust. The bike otherwise runs beautifully and I've put some miles on it so far this summer, though I'm not working it too hard in case the head gaskets give again. Overall, the bike is visually in great shape now (aside from incorrect toolbox decals) and I'll be showing it at the Carnhell Green Vintage Rally here in Cornwall on the 13th August. This show always attracts a large entry, with plenty of AMC - including a G9, which was a Gordon Jackson bike I believe.

Thanks for your help!

[Groily]

Can't remember all the things we all said before Craig - but if the heads have been gas-flowed, look very carefully to ensure there isn't a leak from inlet tract to a pushrod tunnel. If there is even a small one, pinhole size, there'll be oil and smoke everywhere. Been there done that and got the T shirt, after a long time searching for the problem, as you have been. Easy for the hamfisted to go through the inner wall, there's not much metal there in fact.
Otherwise, all the stuff about heads, gaskets, spigots, pistons, rings and oil system apply. There are only so many things that can cause puddling of oil on the top of the pistons and force it to trickle out of the pipes after all!
Are you absolutely CERTAIN the piston rings are a correct fit -up and down height - in the grooves?
On the oil distributor bush you mention, there are in fact two sorts. One with a 'ole, one with a flat - they should interchange and not cause grief.

[craigcc]

Thanks!

Hmm, the trail seems to be increasingly leading to those heads ....
Yep, rings checked and double checked for all ways of measurement/gaps etc. Confident this isn't the issue.

[clive]

Nice looking bike, persevere. My twin had no oil pressure relief valve fitted (as was the case with some years) as a result leaked oil from the joint between the crankcases around the filter tunnel. Modified it with the later filter and relief valve (or rather a much more competent mate did) and now use 20/50 with no recurrence.
Given that you have checked the new valve/guide clearance ( even the club spares scheme can, occasionally of course) be supplied with duff stuff, if it was me I would be now be suspicious that whilst the head seal may be in good condition to look at it may not be flat, or may be flat but not at 90 degrees to the head studs. This might result in uneven pressure on the gasket. It seems likely that this is the problem.
The only other issue I remember reading on here is that some piston rings have to be fitted a specific way up or instead of scraping the oil back down the barrel, they scrape it up to combustion chamber. Can the more knowledgeable confirm?

[oldandsmelly]

I do sympathise trying to fix issues like this. There have been loads of suggestions in this and previous posts and it sounds like you've lucked out on hitting the right answer.

For my twopenneth, I think it's very unlikely that the fault is with the usual suspects for oiling - guides, rings etc. Not just because you've replaced them ( I know that new parts aren't always great), but in my experience for an engine to continually smoke as bad as yours and to be spitting oil out the exhaust usually means some mechanical catastrophe like a broken ring etc which you don't have. I've come to the conclusion after the years that most engines will run OK for ages even when badly worn and not be a problem til something breaks. As the top half of your motor is relatively new, I think your problem comes from below.

I suspect that the crankcase oil level is too high hydraulically forcing oil up the bores. What makes me suggest this is that the symptoms you describe are the same as when I've started my bike after standing for maybe a couple of weeks ( i.e. not long enough to think i have to drain the sump) and then I get a garage full of smoke and oil weeps past the exhaust / head joint and spatters out the exhaust. In my case it all clears after 5 minutes as the scavange does it job reducing the oil level in the crankcase. Could it be something like the oil pick up pipe being damaged/too short/ holed?

Anyhow, good luck with it. That's a very pretty bike!

[clanger9]

Hi Craig,

Quick question: do the spark plugs get fouled with fouled with oil, or do they stay clean? With as much smoke as you describe (and oil from the tailpipes!), with that much oil in the combustion chamber then you'd expect the plugs to foul pretty quickly.

If the plugs are clean, then I'd be looking very carefully for some sort of crack or porosity downstream i.e. into the exhaust port or around the exhaust valve guide...

PS: nice bike, definitely worth getting it sorted.