Author Topic: EW engine repair - help needed urgently.  (Read 12744 times)

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Offline alwyn

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EW engine repair - help needed urgently.
« on: 19 Jan 2007 at 06:00 »
Hi all,
A friend and fellow member of LDMCC name of 'Rien', is battling to get his 1926 EW (Engine # YE 13038, frame # MF 17802) ready for the ADCR - being more of a practical person than an IT literate one he has appealed for help in making this posting and in relaying his appeal for information - he provided me a draft which begins by relating an account of restoration work carried out to the motor some time ago. As he relates in the account the engine suffered a seizure some time following the restoration work - Rien has posed some questions beneath the account that hopefully will be answered by those savvy about the particular matters.

In his account Rien writes...

"Had barrels bored out and honed to suit Honda motorcycle CB 750-K2 oversize pistons, 62 mm., (aluminium pistons with three (3) rings, solid skirt and 15 mm gudgeon). Dimension centre of gudgeon to top of piston was the same as the Douglas cast iron pistons. Brass bushes were made and fitted to the pistons to reduce the gudgeon pin holes to 12.7 mm to enable reuse of the original 1/2" Douglas gudgeon pins.

"Following the engine seizure the barrels were removed and it was found that the clearance between the piston and cylinder wall was 0.006" on the front cylinder and the rear one had 0.004" clearance - it was the rear cylinder that seized. The seizure damaged both the piston and the cylinder wall - the front cylinder was undamaged."

Rien raises the following questions...

(1) Is there a piston, aluminium or cast iron with a 1/2" gudgeon pin available that could be utilised in lieu of the Honda ones used in the previous rebuild?

(2) If an alternative is suggested what modifications if any might be required to that alternative piston to make it suitable?

(3) What clearance is needed between pistons and cylinder bore?

(4) Is there any modifications to the lubrication system recommended?

(5) What type and viscosity of oil is recommended for best engine lubrication?

(6) What thread specifications will apply in the fabrication of a puller for the flywheel, e.g., diameters, type of thread, TPI and thread angle.

(7) What distance should the straight section of the crankcase breather pipe (the one that runs to the drive chain) project into the crankcase and is the end of the pipe within the crankcase cut square or shaped or modified in any way?

Any help and positive comment offered will be relayed to Rien and I'm sure will be much appreciated.

Alwyn



Quotable Quote - "640 k should be enough for anybody"! - Bill Gates - 1981.

Offline Stuart Lister

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Re: EW engine repair - help needed urgently.
« Reply #1 on: 19 Jan 2007 at 07:56 »
Hi Alwyn,

Why use third party pistons at all? Genuine Douglas pistons are not particularly rare or expensive. (I've had a couple of pairs in the last couple of years that I've had to buy because they were included in a box with bits that I needed - I've sold them now, sorry.) It might be worth asking Bantom John in Sheffield (44 1246 290021). He had a few pairs of NOS ones last time I spoke to him - though that may be two years ago now. Failing that, an advert in the NCR or here on the forum might just find a pair.

Hope this helps,

Stuart.

Offline Ian

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Re: EW engine repair - help needed urgently.
« Reply #2 on: 19 Jan 2007 at 08:00 »
I am not surprised that the rear cylinder seized at only 4 thou - although it is the one that runs cooler I believe !! 6-7 though should be plenty. Doesn't seem to me to have been a problem with the piston itself. How badly damaged is the bore ? If it only seized and put mild scrapes in bore and piston then honing it out a few though would fix the problem. The piston can be dressed. Bad grooves are a different matter.

For new pistons if required JP in SA would make them - they don't appear to have EW ones as standard though so may be custom - worth giving them a call.

I hope Rein gets it fixed quickly and puts his entry in for the ADCR !!

Offline trevorp

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Re: EW engine repair - help needed urgently.
« Reply #3 on: 19 Jan 2007 at 09:51 »
Rear cylinder will run hotter and 4 though piston clearance is too small, this is piston clearance we are talking not ring gap
dont have the specs but i bet doug knows

Offline Ian

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Re: EW engine repair - help needed urgently.
« Reply #4 on: 19 Jan 2007 at 19:05 »
Trevor, my understanding is that the front cylinder runs hotter due to lack of oil on the fore and aft twins - not sure if EWs were still that way though with the "improved" oiling system.

Offline roy

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Re: EW engine repair - help needed urgently.
« Reply #5 on: 19 Jan 2007 at 20:30 »
Hi folks, I admit I am not a mechanic in the sense that I know how everything works, but for what its worth, on my EW the gap is about 6 thou. I also find that the rear cylinder does run hotter than the front. I am using Castrol XL 30 oil and so far have not had any problems. Roy.

Offline Chris

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Re: EW engine repair - help needed urgently.
« Reply #6 on: 20 Jan 2007 at 07:20 »
In respect of bore clearance, interestingly, J&P pistons specify only 4 thou. clearance on their current production pistons for the slightly earlier 2.3/4 hp models (up to 1926). However, this clearance only applies at one place as the pistons, in line with modern design, are oval and taper turned. A desirable feature of pistons in early engines is the absence of a bottom ring and indeed to further encourage good bore lubrication, a ring of holes in the side wall of the piston may be provided. From correspondence I have received over the last few years, Rien is not alone with his problem as many owners have experienced problems of nipping up and seizure on the EW models using alloy pistons which originally used cast iron pistons. I even know of one owner who has given up on alloy pistons and reverted to cast iron to avoid the need for constant pulling down and re-honing until they finally eliminate the problem.

The dimensions of the thread for the flywheel extractor are 1.7/16" x 26tpi. I am not certain of the thread angle but with 26tpi it is probably cycle thread and therefore 60 degrees. I have recently produced a drawing of the one I have for another member and have placed this in the REFERENCE section of the Forum under Douglas Motorcycle Technical Articles, here. Special care needs to be taken removing this design of flywheel and temptation to use methods other than the correct extractor should be resisted. The wall of the flywheel beyond the central hub is not much more than 1/8" thick and the use of a three legged puller on the rim will inevitably distort the whole flywheel and not necessarily symmetrically, leaving it with a severe wobble.
« Last Edit: 20 Jan 2007 at 11:47 by alwyn »

Offline Doug

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Re: EW engine repair - help needed urgently.
« Reply #7 on: 21 Jan 2007 at 04:54 »
Douglas did catalog a Sports version of the EW with aluminum pistons. What they actually had in them is another matter. I have a Sports version of the 600EW, also cataloged with aluminum pistons, but actually it yielded up cast iron pistons on standard bore!

I would think for the 350cc EW, 0.0045-0.005" clearance at the bottom of the skirt and perpendicular to the gudgeon pin would be adequate for a modern cast silicon-aluminum alloy piston such as the Honda CB750. But there are a lot of things that could cause the piston to nip up. You say the engine had been rebuilt, but how well was the job done? A miss-aligned crankshaft (built up from various pieces of different cranks) or a bent connecting rod (they are kind of flimsy) will tip the piston in the bore, highly load it, and cause it to overheat, expand, and seize. This could cause it to seize on the side of the piston, in line with the gudgeon pin, in which case it would be obvious something other than the piston just being fitted tight was the matter. Or if the alignment was not too greatly impaired, the piston could run hotter than normal, in which case it might just seize where the clearances are the smallest, at the bottom of the skirt and perpendicular to the gudgeon pin. I had one engine where the piston was picking up at the top of the skirt; cause was the big end roller bearings were seizing.

I do not know if it is the practice on Japanese motorcycle pistons, but in the automotive world the wristpin is often offset to one side of center to reduce the side loading on the piston on the power stroke. Putting a set of these pistons in a Dougie would change your timing, and you may be running with ignition more retarded than what you though you set for. It may be enough to overheat the piston and expand it to seizure, though one would expect tell tale signs on top of the piston crown. There is the possibility of having each piston offset opposite ways, so you could never time the engine equal on the front and rear pots!

Is the ignition timing correct, is it jetted too lean? This will cause it to run hotter than normal, and the tightest piston will nip up first.

When it is said the distance from the gudgeon pin to the top of the piston was the same, top of the piston means the top of the first ring land or the top of the crown? The Honda pistons are likely crowned, where as the original EW pistons would be flat.

Lack of oiling is probably not the problem, as the rear cylinder tends to get more oil than the front. This is because the crank throws oil from the bottom of the crankcase into the rear cylinder. This does make that cylinder run cooler, but this is probably more than negated by the poor air cooling of the rear cylinder. It is often repeated the strange but true tale that the rear cylinder on a motorcycle runs cooler than the front because it receives some assistance from 'oil cooling' and also that the front cylinder runs in the lee of the front mudguard. But I think this old chestnut pertains to big American v-twins, where there was a fat tire and huge mudguard to block the wind to the front cylinder, and the rear cylinder is not as effectively buried behind the crankcase as it is on a Douglas fore and aft engine.

Boring out for a loose fit is a poor engineering practice, and tends to promote excessive amounts of oil getting up by the piston and rings, and burning of oil in the combustion chamber. Plus you have an engine that is starting out half worn! Better is to gently break in the engine and ease the high spots down on the piston. This of course means stripping down the engine multiple times, as well as taking a lot of time and patience that few have these days. It is quicker and simpler to treat the symptoms and not the cause. Better yet would be to find out why, with the proper clearances to start with, was the engine tightening up.

Re- point seven, I think you mean that the pipe projects into the timing chest? This stand pipe should be high enough that the teeth of the lower cam wheel are fully submerged in the oil, which will then transfer oil to the rest of the gear train, cams, tappets, etc. When the engine is running this level will be drawn down to a certain extent. As long as this is achieved, any additional oil is surplus, and is lead off via a pipe to the primary chain. It is common that when the bike is parked and the oil drains down to the bottom of the timing chest, the level rises and goes out the overflow pipe, and leaves a puddle on the ground under the machine.

-Doug

Offline riengerr

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Re: EW engine
« Reply #8 on: 04 Mar 2008 at 07:34 »
Hi,
For the Centenary Rally I fitted J.P. Aluminium Pistons, with 2 comp rings, 1 oil control ring.  Crankshaft and conrods looked okay, no obvious play in B.E.  rollers and races.  On the rally engine seized up 3 to 4 times, waited to cool down then go again.  Kept going to the end of the rally, with no loud noises.  Checking spark plugs a couple of times, found rear plug a good colour but front plug nearly white.  Indicating running too lean, creating more heat.  Carburation is a problem, B & B carburretor fitted. Adjust original airscrew for good idle and start.  On roads runs rough, missing, adjust airscrew for more air, engine running and performance good, but now won't idle.
After rally checked pistons and cyl again.  Front and rear pistons had seized, cylinders slightly marked.  Measured pistons across skirt realised pistons not cam ground.  Went back to J.P Pistons. They supplied me with 2 new pistons cam ground .010", plus rings.  Honed cylinders to clean up pistons skirt clearance .0065".  Assembled engine, goes ok. Still running lean of front cyl, no airleaks. Still have same carburretor problem.   Fixed idle fuel jet-fuel entry 2 orifices are damaged.
What size is the orifice size for the main fuel jet?
Anyone know what size the orifice should be? 
I am a retired motor mechanic, do most work myself.
Rien

Offline davebarkshire

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Re: EW engine repair - help needed urgently.
« Reply #9 on: 04 Mar 2008 at 10:06 »
I may be wrong here but I think that the B&B was from the era where carbs were not considered to be 'fully automatic' and from what I understand it was normal practice to use the air lever not just as a choke but as an active control to suit the situation. Maybe closing the air lever a little when not ticking over would correct the mixture?

My 1926 Ariel has a B&B and sometimes the engine coughs and spits a little so by closing the air lever the engine comes back on song. I also have a Royal Enfield with a B&B which runs rich most of the time and I constantly thrash the nuts off it without any trouble.

Offline Ian

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Re: EW engine repair - help needed urgently.
« Reply #10 on: 04 Mar 2008 at 20:07 »
My understanding is that most of the models run much hotter on the front cylinder. When my clutch failed on the OC I got an opportunity to look at the plugs when they had been running at high speed - and the front one was very pale - back one almost black.

Its to do with cooling flow and the amount of oil getting to each cylinder I think.

Offline Alan Cun

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Re: EW engine repair - help needed urgently.
« Reply #11 on: 05 Mar 2008 at 08:15 »
Hello All, I did an article on Tecnical Articles 18 Aug I think on Smoking rear cylinders of 3 E29 cycles on a rally cant seem to retrieve it for some reason but maybe someone can.  Alan

Offline Doug

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Re: EW engine repair - help needed urgently.
« Reply #12 on: 05 Mar 2008 at 10:26 »
Hello All, I did an article on Tecnical Articles 18 Aug I think on Smoking rear cylinders of 3 E29 cycles on a rally cant seem to retrieve it for some reason but maybe someone can.  Alan

This is the link to it here-

https://www.douglasmotorcycles.net/index.php/topic,2267.0.html

-Doug

Offline Alan

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Re: EW engine repair - help needed urgently.
« Reply #13 on: 07 Mar 2008 at 01:41 »
 For my B29 restoration here in Aus, I was recommended a piston that I was told was often used for EW's and similar...this was from a Suzuki Swift Car (models of a decade or so ago and much loved by boy racers, not the latest offering and not sure what they were sold as in Europe)...apart from a bit of work on the gudgeon pin side of things (nothing complex), in these went and no problems to date even running on a hot day...Hope this helps but measure up and crosscheck first....Alan