Author Topic: Mk4 Camshafts / followers are showing signs of wear  (Read 3894 times)

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Offline Mike of Woking

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My Mk4 Crankshafts are showing signs of wear. The chrome plate surfaces in the cam lobes are starting to break up. I though I would look to getting them reprofiled. There is nothing wrong with the base metal, they simply need the chrome removed, rechromed and then reground. Can anyone recommend a local firm in Surrey who can do re-chroming and grinding ?

If anyone can provide the cam lift dimensions for the Mk 4 that would be useful, unfortunately I do not have the original drawings. Just provide me with the dimension of the new finished cam from the top of the lobe to the opposite end that will suffice.

Incidentally I have just had new cam followers / tappets made from Royal Enfield Bullet blanks available from Hitchcocks @ a basic cost of 6.50 each, which have identical 3/8" dia spindles, longer and also have larger diameter feet. So to make them fit they need to be cut down in length, reduced to 7/8 " dia at the foot and a chamfered hole drilled in the other end to accommodate the Mk4 push rod small ball end. The machining cost is extra. The item then needs to be re-case hardened where machined. Overall they come in at just under a tenner each. The standard Douglas component has hard chrome on both ends, but depending on the mileage you intend to do, you may decide that this is not worth the extra money. Certainly I am going to leave mine case hardened as I don't think chrome on chrome is a good thing. If there has to be a sacrifical lamb, then I prefer the followers to wear out first rather than the cams !

Many thanks for your help,

Mike


Offline eddie

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Re: Mk4 Camshafts / followers are showing signs of wear
« Reply #1 on: 06 Jan 2012 at 17:52 »
Mike,
         If your cams or followers are chrome plated and now starting to peel, I fear you have more problems in store. Firstly, chrome plating is not to be reccommended for recovering highly loaded components such as roller bearings or cams and followers - the high loading tends to make the plating creep, and eventually break free from the parent metal. The loose fragments of chrome then get transported by the oil and being glass hard, attack any other moving parts, especially the bigend bearings. An even bigger problem occurs when these hard grains get embedded in soft metal like alloy pistons - which then become hones that wear away the bores.
        The factory never supplied chrome plated cams or followers, so to put the records straight, original Douglas cams and followers were made from case hardened EN32 steel (or an equivalent). This is where most of the wear problems started as it is bad practice to run two loaded components together when made of the same material. Dissimilar materials - say EN32 & EN36 - have much better wear characteristics under these conditions. If your cams have been chrome plated, then they were probably ground down first so that the finished job would have a constant thickness of plating - this has probably resulted in the case hardened skin being absolutely minimal as the original blanks were only case hardened to a depth of about 25-30 thou (before grinding).
       Moving on to your attempt to use Royal Enfield followers - if you are going to modify and then re-harden them, you are likely to have distortion problems due to the heat involved. Easier routes would be to use new followers from the LDMCC spares scheme or have your followers faced with 'Stellite'.
      From your posting, you seem to have oversimplified the process of cam grinding - the base circle diameter and the lift are only 2 of the critical dimensions - you also have to take into account the opening and closing angles and the cam profile. For reference, the standard 'T' cam used in the Mk4 had a base circle of 1.000" dia and a lift of .187".
            Regards,
                         Eddie.

Offline Mike of Woking

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Re: Mk4 Camshafts / followers are showing signs of wear
« Reply #2 on: 06 Jan 2012 at 22:22 »
Thanks Eddie,

I appreciate your comments. I assumed that my cams were unmodified and hence standard with hard chrome plate on copper plate. Obviously I was wrong as they have must have been repaired by the previous owner, who as father and son owned the machine for most of the last 60 years. No possibility that I will put the cams back in place as they stand.

My first thought was to replace both cams and followers though the LDMCC spares schemes, but I am still waiting for a reply to my e mail to post war spares sent early December. Very happy to buy them if they are available - perhaps you can advise if the club has spare camshafts ? Without a telephone number sending e mails seems to be a bit hit and miss.

Duly noted your comment about case hardening distortion to the modified followers - I will get them finish ground afterwards. Thanks also for the dimension of the cams. If I have to get them reprofiled, then I will get them stellite faced and reground. Hopefully I can get new ones from the club sooner rather than later. Trying to get the bike back on the road for Spring.

Regards and thanks again,


Mike

Offline eddie

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Re: Mk4 Camshafts / followers are showing signs of wear
« Reply #3 on: 07 Jan 2012 at 08:06 »
Mike,
        As you have no doubt already found, quite a few components in the Douglas engine are copper plated. This is done to provide a barrier to the carbon enrichment that is part of the case hardening process. The part is copper plated and then the plating is removed from areas that have to be hardened (cam profiles and bearing journals) - the part then goes through the case hardening process, but only the bare areas actually get hardened. This gives good wear resistant surfaces without unduly affecting the strength of the rest of the shaft. The copper plating is not there for cosmetic reasons or as part of further plating processes.
            Regards,
                          Eddie.

Offline David Lawrence

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Re: Mk4 Camshafts / followers are showing signs of wear
« Reply #4 on: 07 Jan 2012 at 21:52 »
Mike,
I was rather disturbed to read of your problems with the post war spares in your post which coincidently I happened to read on Friday, I had planned to meet up with Patrick on Saturday at the Newark show and so raised your problem with him. He claims not to have received your emails, therefore, to solve the problem I would appreciate it if you could email me your home telephone number and a time to call you at your conveniance, to my old address that I used in my stint as Club registrar:
dougregister@sky.com
Hopefully we can then come up with an explanation and a solution!
We do have some cams in stock and have just recently taken delivery of a batch of cam followers, we were aware of the need for high quality for these and had them made by a respected cam grinding company, even so were a bit surprised at the cost!! OK there not cheap but are good quality!
I will not be back to Essex until Monday evening but will call you asap
Cheers
Dave