Author Topic: Mark V timing side main bearings  (Read 3717 times)

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Offline steveL

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Mark V timing side main bearings
« on: 03 Feb 2011 at 20:22 »
Hi all,

As a very new Douglas owner (well several boxes of bits), does anyone have any good tips about getting the timing side main bearings replaced on a Douglas Mark V (2 phosphor bronze 'top hat' bearings).

I'm based in the Midlands and would appreciate anyone whos had experience of a local supplier doing this letting me know.

Cheers

Steve.

Offline eddie

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Re: Mark V timing side main bearings
« Reply #1 on: 04 Feb 2011 at 08:25 »
Hi Steve,
               It will pay you to modify the front main bearing bushes to the the type used in the earlier Mark 1 & 3 machines. The Mark 4/5 arrangement has 2 narrow bushes which tend to work loose in the crankcases - this rarely happened with the earlier single bush. You will probably have to get an oversize/undersize bush made, as your crank and/or cases will probably be worn. Have the bush made to the same overall length as the pair of bushes when pressed into the crankcase. With the bush fitted from inside the crankcase, the nose will project into the timing cover by the thickness of the flange on the original front half. Having done this mod, you can then do away with the oil retaining plate (behind the timing gear). Replace this with a spacer of the same thickness and slightly smaller in diameter than the front journal on the crank. The crank and cases can now be assembled. Push the crank forward to contact the face of the front main bearing. Compare the depth of the spigot on the clutch release with the depth from the back of the crankcase to the rear main bearing. Subtract 5 thou from this figure and shim the bearing accordingly. Fit the clutch release and pull the crank back against it - this will give a 5 thou running clearance on the front main bearing. The crank will now be held against the rear main bearing by the action of the clutch springs, and any movement due to different expansion rates is taken on the front main - as it has now been freed up by removing the oil retaining plate. This results in a freer running motor, the rear main bearing does not work loose, either - and the clutch adjustment is not affected by the temperature of the engine.
       After fitting, the front bush should have 3 thou clearance on the shaft - I know that sounds a lot, but any less usually results in the bush nipping up and turning in the case - causing the locating pin to distort the flange (only cure is another stripdown!).
        Good luck with the build,
                                 Regards,
                                            Eddie.

Offline steveL

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Re: Mark V timing side main bearings
« Reply #2 on: 04 Feb 2011 at 12:28 »
Thanks Eddie.

A pretty comprehensive reply!
Much appreciated.

I'll let you know how it goes.

If anyone knows of a reputable company in the Midlands that can do that, drop me a note.

Steve.

Offline Sheikh Pip

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Re: Mark V timing side main bearings
« Reply #3 on: 04 Feb 2011 at 18:33 »
Hi Steve

You could try E&D engines at Bilston, 01902 402884, the guy in charge has restored a few bikes, he was really helpfull when I visited him for a quote on my cylinder rebores, and very cheap at 20 per barrel. He was very friendly, showed me an Ambassador he'd nearly finished restoring, a few guys at work who have had work done by him recommended him to me, so he should be OK!

Phil

Offline steveL

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Re: Mark V timing side main bearings
« Reply #4 on: 06 Feb 2011 at 15:15 »
Hi Phil, Eddie

Have been to see E & D and dropped off the crank and cases (well its got to be done, and I don't have the facilities or more importantly the skill to turn the bearing and press it into the crankcase). Saw the ambassador - very nice.

They certainly have a lot of engines to get through, but handily for me they're open on a Saturday.

Can either of you confirm that the oil retaining plate has a thickness of 0.1 inch ? I've checked what I think is the existing oil retaining plate thickness, but just want to double check.

Had the frame blasted and painted. Found a good place for blasting in Birmingham, Sutton Sodablasting (www.suttonsodablasting.co.uk).

I'm resisting the temptation to put stuff back together as it comes in as I think getting everything done first is key.

I'd like to get the engine and gearbox complete and put in the frame, and then put on the forks, rear sub frame etc.

Have joined the LDMCC, next things to get are speedo and seat. I see on ebay there are loads of sub 30 speedos (Smiths replicas) which look as if they'll do the job, anyone used one ?

Steve.

Offline eddie

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Re: Mark V timing side main bearings
« Reply #5 on: 06 Feb 2011 at 16:27 »
Hi Steve,
                Yes, the oil retaining plate is .100" thick. The cam drive pinion abuts the plate, so it cannot be any thicker - as it will rub on the back of the idlers.
        Sorry, but I can't comment on the replica speedos as I have not had a need to use one! They are sold as replica Smiths units, but I suspect they are magnetic units rather than Chronometric.
                     Regards,
                              Eddie.

 

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