Author Topic: G31 springs back in to life  (Read 7078 times)

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Offline alexd912

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G31 springs back in to life
« on: 26 Jul 2009 at 20:01 »
Hi all,

Well after a few teething troubles and a quick check over the G31 was tearing up the local Finnish roads at just over 100Kmph.

I wanted to get your opinion on some issues with the bike, as I have mentioned in some of my earlier posts my aim is to get the bike close to original as possible.

So in the attached pictures I have circled some areas that Im not sure if they are correct.

In the pictures of the decompressor there is a hole and I can fell air coming from this, is this correct or should there be a stud/bolt there?

Also there is a picture where there is a hole and you can see the chain going to the gearbox, what is the purpose of this hole and should it be covered?
Also what is the link pitch of this chain as I would like to replace it with a O-Ring chain.

In one picture there appears to be a stud missing from the head/rocker cover. Is this something that needs immediate attention? Currently the bike is not loosing any oil at all:)

I have also included some other photos and I will attach more later.

As for the bike she seems to run very well and I have added a 12Amp/h battery that I fitted in to the old battery, see other post for pics for anyone thats interested....

I just need to locate a Dynomag now for it!

All comments as always are very welcome and if anyone happens to come across spares for this bike PLEASE let me know:)

Regards

Alex













Photos added to database - Dave, 31st July 2009
« Last Edit: 30 Jul 2009 at 22:29 by Dave »
Best regards
Alex
1930 Douglas G31

Offline Doug

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Re: G31 springs back in to life
« Reply #1 on: 27 Jul 2009 at 03:14 »
Alex,

First picture. No idea why there is a hole in the back of the primary chain case. That area of my similar 1934 model is broken away so can not confirm if it is the same. However pictures of another F/G31 taken at a Bristol Cavalcade show a similar hole. Perhaps a discrete means to check the primary chain tension? Douglas was only just getting around to fully enclosing the primary chain, in fact the 350cc side valves of 1931 still only just had a sheet metal cover over the face of the chain with no back cover. So a small hole with no cover probably would not have bothered the Factory that much.

I would forget about o-ring chain. There is typically just enough room for standard chain spring link between the other chain run and the grease slinger on the clutch disk. And sometimes not even that and all rivited chain is required. I doubt you will find room for the wide plates of the heavy, modern, o-ring chains. At least not those I have seen sold. 

Second picture. You are missing one of the bolts that hold the two halves of the crankcase together. It would be identical to the one directly above. I am not sure why you are feeling air emitting. Clearly it is crankcase pressure, but the drilling does not break through into the crankcase chamber. It must be minor leakage into the bolt hole at the gasket joint. There should be a hole on the opposite side of the crankcase too, unless the head of the bolt broke off and is still insitu.

Fourth picture. You are missing one of the grease/oil fittings for the rocker arms. There is an example at the other end of the head. These screw directly into the ends of the rocker spindles; they have to be removed to remove the rocker covers, but do not contribute directly to securing the outer cover to the inner rocker cover. You may want to replace these with angled Zerk fittings. Not original, but more practical and easier to get a grease gun on and apply the necessary. The the original fittings, particularly on the rear head, are nigh impossible to get a Techmite (?) gun on. It was probably removed so a few drops of oil could be dropped down the hole from a standard oil can before every outing. You could just fit oil cups.




-Doug


Offline alexd912

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Re: G31 springs back in to life
« Reply #2 on: 27 Jul 2009 at 15:50 »
Hi there,

So Doug it looks like I have to remove the Carburettor housing and the oil regulator assemble to replace the stud then? Do you think there is any urgency to replace that as I will probably end up removing the engine in the winter to check everything over...

Do you or any other members happen to have any spare oil feeders for the rocker covers??

Thanks in advance.

Best regards

Alex
Best regards
Alex
1930 Douglas G31

Offline Doug

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Re: G31 springs back in to life
« Reply #3 on: 28 Jul 2009 at 02:40 »
Alex,

Considering that there are only six bolts clamping the two halves the the crankcase together, I would not care to be down to only five! You will have to remove the timing cover and the idler gear to get at the head of the bolt (if it is present.)

X marks the spot.




The oil regulator (sightglass) can stay attached to the airbox, but you will need to remove the carb to access some of the small nuts holding the timing cover on. You may want to mark the gear timing with a grease pencil or something before removing the idler gear.


-Doug
« Last Edit: 28 Jul 2009 at 02:48 by Doug »

Offline alexd912

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Re: G31 springs back in to life
« Reply #4 on: 28 Jul 2009 at 18:27 »
I spoke too soon:(

So I took the bike for a longer run today 22km, and after around 18 km the bike started to seize, so dumped the clutch and coasted to stand still. I waited a few mins then kicked her over and she sparked back in to life and away I went for the remaining 4 or 5 km.. On the way back the engine seized again at almost the same distance, 18km... Once again waited for a few mins and then back on my way home with no further issues..

So a few things I tried after the first time, I increased the oil drip to 2 turns out from the 1.5 turns I had. I also turned the air screw on the carb a further one turn out, making 2.5.

But after all that it still seized..

Any thoughts anyone???

One thought comes to my mind and that is as I do not know the history of the bike, albeit it has been restored at some point recently im wondering if the engine was rebuilt during the restoration and then shortly after that the wiring burn out and thus it never got finished running in....

As for the engine after this "longer run" I noticed oil coming from where the barrels meet the engine casing and some oil coming from where the magneto meets the casing by the top gear showing on your picture with x marks the spot.

See the red arrows of death on the attached picture..

Now I have sometimes heard that after an engine rebuild you naturally have to run it in then re tighten the cylinder/barrels etc...

As you have all guessed im very VERY new to the Dougie world so any help would be appreciated-..

I realise that I will have to take part of the engine to bits to replace the broken stud soon, but was hoping to get some use out of it..

Regards

Alex





Photo added to database - Dave, 31st July 2009
« Last Edit: 30 Jul 2009 at 22:33 by Dave »
Best regards
Alex
1930 Douglas G31

Offline Doug

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Re: G31 springs back in to life
« Reply #5 on: 30 Jul 2009 at 01:14 »
Alex,

The fact that the oil is leaking out the timing cover joint and from around the magneto is actually a good sign. It proves that the oil is at least getting that far. You know the old adage that when your British bike stops leaking oil, it is because it ran out.

However the fact that the oil is getting into the engine, does not mean that it is getting to where it belongs. First the leak is probably nothing more than a bad timing cover joint gasket, or lack of one. The oil is leaking out rather high. Normally the level in the timing cover is enough to submerge the lower run of the gear train. There is a 1/4 inch hole that communicates and drains off the excess into the crank chamber that sets the oil level.

Inside the timing chest cover is the oil pump. It is possible that on the delivery side the joint face gasket has failed, allowing the oil to hemorrhage out into the timing chest, rather than being delivered to the crankshaft. Oil fed through the crankshaft and escaping from the big end bearings is what lubricates the cylinder bores. Since the sump is scavenged, you do not have any remedial splash lubrication. The oil pump has, or should have, a primitive pressure relief valve. If this is stuck open, spring rotted, or what ever; oil returns from the pressure side back to the delivery side without ever leaving the pump. There is a spring loaded quill that feeds the oil into the end of the crankshaft. If the spring is weak or omitted, the oil may just leak out into the timing chest rather than enter the crankshaft. Or if the internal galleries in the crankshaft are plugged with sludge the oil may not enter. However if the crankshaft were not getting any oil, you would be seizing the connecting rod bearings and not the pistons. And if you seized the rod bearings the engine would not be freeing up when it cools down. (Also due to the scarcity of crankshafts you will have converted you motorcycle into a static museum piece!)

So assuming the oil is getting into the crankcase chamber via the rod bearings, the problem maybe the pistons were fitted with the improper clearance. I have had pistons that have been made of unsuitable grades of aluminum that had excessive rates of thermal expansion. I had one set of 1950s aftermarket NOS pistons fitted to my '34 that kept seizing. I kept easing down the tight spots till the pistons rattled and it still kept seizing! A different and more reputable brand of piston was the solution.

But first I would just try increasing the oil delivery, a lot. Is the engine burning oil? If not, increase the oil rate till it does smoke like a navy destroyer hiding for cover.  The number of turns on the sight glass needle valve is meaningless; as are the numbers on the dial. What counts are the number of drips per minute. The faster and harder you use the engine the more these should be increased, but since the oil pump and valve are not throttle controlled, you have to compromise. But it is better to start out will too much oil and foul a few plugs, than to have too little and, well, seize the pistons. It is hard to say how many drips per minute to start with, a new tight engine needs more than one bedded in. Again, start off with the engine smoking and cut it back in increments. If the anti-fouling pockets are still intact the engine ought to tolerate a over abundance of oil, though your neighbors and the environment might not!

-Doug

-Doug

Offline Doug

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Re: G31 springs back in to life
« Reply #6 on: 01 Aug 2009 at 05:55 »
Quote from: Doug
Second picture. You are missing one of the bolts that hold the two halves of the crankcase together. It would be identical to the one directly above.

Correction, it has come to light that it is not the crankcase bolt that is missing. The crankcase bolt was lengthed and used to secure the primary chaincase (see next image, the end with the nut is just visible behind the flywheel.)



The bracket for the clutch and exhaust valve lifter cables does not use the pair of crankcase bolts as it does on the Dirt Track models, but was cut short and had its own second stud to secure the lower end. Presumably a stud as they could have used the same inventory that they used to secure the magneto clamps. It is this short stud that is missing. Also this hole is drilled and tapped right into the crankcase chamber (there is nothing but a void behind it) and this would explain why there is crankcase pressure blowing out of the hole while the engine is running.

-Doug

 

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