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Sat Jun 07, 2008 11:05 am

Hi Everyone,

Just after a bit of advice before i take my engine bits to the machine shop.

I have the following cam / crank combinations from 2 engines I have dismantled to get good parts for my 47 engine rebuild.

1. Good alloy cam +2 and crankshaft 1st undersize needs work

2. good condition fiber cam (no lash number marking that I can see) and std crank in very good condition

I plan to use the std size crank so I can use the NOS std bearings I have, my question is should I use the fiber cam that was paired with it or the alloy cam from the other engine, if I use the alloy cam should I get the machine shop to swap over the corresponding cam gear from the other crank ?

Any advice appreciated

Cheers
Kev

Sat Jun 07, 2008 8:17 pm

Kev with out physically seeing the situation it hard to make a judgemnet call. However, I personally would do away with the Fiber and stick with the alloy' you can use the the gear on the crank already and swap it to the one you where talking about ! Or Buy a new crank cam timing gear and let the alloy cam gear wear in on the new crank timing cam gear. Eitherway go alloy.

Mon Jun 09, 2008 2:37 pm

Thanks Eric, I have followed your advice and will use the alloy cam, also done your backlash test detailed in another thread on the subject, luckily this alloy cam passed the test with the good crank I have without swapping the gear over.

Your reply has confused me a bit, I always thought the cam gear was matched to the gear on the crank from new hence the -2 - +2 numbers but from your reply I assume the gears are not matched until they are worn in ? meaning any cam number was used in initial production. Am I understanding that right ?

Cheers
Kev

Mon Jun 09, 2008 5:31 pm

I believe that the cam gear number was a tolerance makeup for the distance between the crank and cam center, the crank gear has no number and all are the same, the number on the cam gear should be a diameter number difference from standard to make up for differences in factory case machine work? correct ?
I guess that a used cam gear would wear in faster if you use a "new" crank gear if there are any new ones left but I would always use the spin test to make sure they were pretty close, +2 and -2 are pretty small differences from standard, I think i have seen cam gears up to a +8 which is getting up there, always spin test if in doubt

Tue Jun 10, 2008 8:51 am

Kev, at the factory in Wolfsburg, That old saying ran true" if the shoe fits wear it" Those boys put those 25 and 36 hp motors together so fast and efficiantly it wasn't funny. Grab ahold of "Car of the Century video" or one of the oldie videos that shows the assy. line action. what they where primarily concerned with "In my Opinion" was functionality. They would put crank and cam gears in do a quick test if it =the cam--didn't walk out of the case on to the next. Mutual wear and tear would take care of the rest.

billmetric your correct in that the offset numbers on the cam gear itself is The degree of measurement to either take up or give moremating surface of cam gear to crank timeing gear or Visaversa. Allowing to within .002 of play which is nothing really. Again the reverse test with cam gear and crank itstalled in the Case half will tell you weather to proceed or use a + or - gear, if the cam begins to walk out of your case!

Wed Jun 11, 2008 12:00 am

billmetric wrote: the number on the cam gear should be a diameter number difference from standard to make up for differences in factory case machine work? correct ?
You can't alter the diameter of the gear. It must be precisely 2 times the diameter of the crank gear. The numbers on the cam gear indicate a slight variation in the helix angle. Altering the helix angle will take up backlash, or add it.

Wed Jun 11, 2008 5:53 am

Thanks Bruce, I would think that as long as the gear had 2 times as many teeth on it the actual size would not be the issue with such a small tolerance, so is the helix angle actually making up for centerline distance with the case machining between the two gears or is it a gear production variation they are compensating? I'm also wondering if the fiber gears had a variation number + or - or was it just the alloy gears that were marked, I would suspect that the fiber gears wore in a lot faster eliminating the need to account for any variations?

Wed Jun 11, 2008 12:32 pm

I think you are right Bill, the fibre cam gear I have has no number stamped on it, also interesting to note the workshop manual states: "The teeth of the camshaft timing gears used on the deluxe are of fibre"

Wed Jun 11, 2008 9:17 pm

Yeah, thats crazy, I think the idea was that the fiber gear was quieter, although on a split with no engine compartment insulation at all how much of a difference could it have made? And of course the metal gear had to be more expensive to make and it was used on the Standard? weird, I do know that Model A Fords again had fiber cam gears also and they are known to strip off pretty regularly, I don't know when the last VW fiber gear stripped out but I've never heard of it happening, probably because no one has reused one in the last 30 years?

Wed Jun 11, 2008 11:46 pm

billmetric wrote: ....is the helix angle actually making up for centerline distance with the case machining between the two gears or is it a gear production variation they are compensating?
I think all of the above is what's happening.
The size and shape of the gear tooth is fixed. So is the space between the gear teeth. If you wanted to change the diameter, either of these must change. But they can't. If the gaps between the teeth increased, they wouldn't mesh properly with the crank gear. Same goes for the width of the tooth.

Mon Jun 16, 2008 4:58 am

mikarta/fiber cam gears are great !!! i have looked inside my car`s engine through the fuel pump hole , and found that after 60kmiles and 57 years , the gear shows no signs of wear ....pushrods and cam itself were in the same condition ....i still don`t know why i bought a nos oem fiber gear camshaft for the day i need to overhaul the engine :?

Mon Jun 16, 2008 5:18 am

Fiber gears had a problem at least here in Finland. For some reason the fiber layer loosened from aluminum wheel. You can guess what happened then.

All 25 engines I have dismantled the fiber wheel cam is changed to aluminum.

In spite of that I assembled a NOS fiber gear for my next split engine. :D