New build engine woes

Information relating to the Matchless G12 or AJS Model 31 650cc twin
g5wqian
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Location: near swindon wilts

Re: New build engine woes

Post by g5wqian »

heads and barrels - use thick base gasket and composite head gasket .

is it leaking from crankcase halves or is it coming out of dynamo hole in timing side , there should be the right cork ring on the dynamo to seal it .

mine initially had a rubber o-ring trying to seal dynamo to case and this was no good , i changed it to the cork seal from amoc spares and used plenty of welseal on it , its fine now .
you can remove dynamo and install it without taking anything apart , it slots in and pulls out easily .
when you install dynamo though use block of wood to push it in with when you are nipping up bolt and clamp straps , dont do the long bolt up too tight though its only a small thread and easy to strip it .
just pull the bolt up dont graunch it .

some head gaskets from amcclassic spares have viton o-rings with them to fit where the oil gallery goes between barrels and heads to try and seal them better .

i tend to find if i keep below 60mph my twin is good , if i go over this speed for long periods i can end up with oil weep coming from top of barrel , my oil pressure is quite high though !! .

another area you get oil depositing itself is the rear wheel and chainguard , this comes from the oil tank breather pipe .
i found if i have oil level at top mark when cold i will get oil coming out and onto back wheel area , it seems if i keep oil level lower i dont have so much of an issue .
obviously the oil expands when hot and level goes up !!

hope you sort it out satisfactorily .
ian
Chessiegolf
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Re: New build engine woes

Post by Chessiegolf »

Thanks for the suggestions.

This engine is the alternator/distributor model so that shoud eliminate a dynamo joint leak.

Perhaps oil over the tyre, swinging arm and silencer is coming from the oil tank breather as the oil was topped up to the outside mark just proir to setting off for home. If that is a source of problems, what is a safe minimum level to run at? A check valve had been previously fitted in the feed line, which seems odd as the feed pump has to suck against that to get the oil flowing. Having said that, oil does seem to circulate ok as there is a steady return flow at anything above idle. Should I dispense with the valve and return to how AMC originally intended?

I bought the bike without knowing any of its history and while it was nice and shiny on the outside, it turned out to be a heap inside, hence the need to spend over £6000 on getting it (supposedly) right! I must add that all of that money wasn't just on the engine, it now has new rims and tyres, a 12v alternator, new front springs, new chains, sprockets, brake drum and complete clutch basket.

Thanks for the suggestion about needing a Dowty washer on the front throat bolt, I'll source that, at least that's a job I feel competent to do.

Is there a list anywhere of torque settings for important things like engine bolts?
Mick D
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Re: New build engine woes

Post by Mick D »

Hi

The oil tank breather should vent via a rigid pipe down the drive side of the gearbox and to the vicinity of the secondary chain - the pipe is visible in this illustration:
Gearbox Adjustment.png
There are very few torque settings quoted in the original documentation, where none is referenced I use common sense, standard length spanners, lubricated threads and moderate force. UNF torque tables can be used as a guide but don't apply the stated torques if you are tightening into aluminium alloy castings.

Regards Mick
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SPRIDDLER
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Re: New build engine woes

Post by SPRIDDLER »

Chessiegolf wrote: Perhaps oil over the tyre, swinging arm and silencer is coming from the oil tank breather as the oil was topped up to the outside mark just proir to setting off for home. If that is a source of problems, what is a safe minimum level to run at?
I'm not particularly knowledgeable about AMC twin engines but the placement of the tank oil level transfer is often more cosmetic than 'correct'. The only way to be sure is to empty the oil out and refill with the amount specified in the manuals (It is specified for gearboxes but not sure if it is for the twin engines :? )
As far as a safe level goes, the oil has to cool as well as lubricate the engine. Purely to answer your question I'd say that half a tank would be sufficient to try out for leakage over maybe 20 or 30 miles. In winter months I have (rightly or wrongly but without any issues) only half filled my single engine oil tank since a full tank of monograde oil never became more than just lukewarm after a spirited ride of 30 or 40 miles.
A check valve had been previously fitted in the feed line, which seems odd as the feed pump has to suck against that to get the oil flowing. Having said that, oil does seem to circulate ok as there is a steady return flow at anything above idle. Should I dispense with the valve and return to how AMC originally intended?
For the moment and since the oil is returning steadily I wouldn't change it as it's unlikely to be the cause of the leakage. It's best to change only one thing at a time ;)

Just a further point re the check valve: It's there to prevent oil from the tank seeping past the pump when the bike is unused (quite common and aka 'Wet sumping'). If it isn't functioning oil will leak past the pump and collect in the crankcase (sump). If left to build up in the c/case it can cause smoking when the engine is started and or leaking joints and or oil-fouled plug(s). Similarly, if oil has drained to the c/case you may think that the tank needs to be topped up but when the engine is started and the oil in the c/case is pumped back to the tank the level in the tank will be too high. When a bike has not been run for a week or two (it varies engine to engine) many owners drain the c/case of any collected oil before starting it up.

Good luck.
'There is a tide in the affairs of men
Which taken at the flood............'
Chessiegolf
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Re: New build engine woes

Post by Chessiegolf »

Just an update...........I removed the seat and checked the oil tank breather, it looks as if nothing has come out of that in a while as the end of the pipe was quite dry.
What I did discover though was, having cleaned off all the oil from underneath, when the engine was run hardly any oil materialised. However, as soon as I had moved the bike under its own steam for 100 yards or so, oil was found dripping again.

I did this twice and think the oil is coming from the gearbox main drive although its hard to see given that the primary chaincase gets in the way of a direct view. The gearbox had been refilled prior to taking repossession and there is none in the first chamber now, so looks like there has been a major failure with the oil seal.

Does anyone know if this has to be a gearbox removal for oil seal replacement?
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ajscomboman
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Re: New build engine woes

Post by ajscomboman »

No the box doesn't have to be removed only all the primary drive and chaincase.
Mick D
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Re: New build engine woes

Post by Mick D »

Hi

I assume you have an AMC gearbox: in which case it does not 'need' to be removed to replace the main shaft oil seal under the sprocket, however it's easier if it's out of the bike. There are also the possibilities of other areas where leaks can occur which should be investigated as they are easier to remedy: the drain and level plugs, the cam plate plunger cap, kick start seal, foot change spindle seal. It can also leak along the sleeve gear into the primary chain case.
Before ripping the gearbox out why not give it a good clean and re-fill it and try to identify where the leak is?

It would be unusual for a gearbox to empty itself via the MS seal over the course of 100 yards, and the correct oil level is below that of the oil seal when static, (I think), so could not drain the box whilst standing. Do you leave the bike on the centre or side stand?

Regards Mick
bob
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Re: New build engine woes

Post by bob »

Also put silicone sealant on the splines and under the spacer , oil can leak here .
BRobbo
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Re: New build engine woes

Post by BRobbo »

You don't mention the gearbox as one of the parts of your bike which was worked on so it would seem an unlucky coincidence if your gearbox has suddenly developed a serious leak. Before undertaking a major stripdown of the primary side you could try using a UV oil leak agent which can be obtained on ebay for a relatively modest price. I have not used this myself but heard good reports from a fellow member who used it to track down leaks in a gearbox. Its use is not confined to gearboxes of course.
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