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MG MGB Technical - Bad Camshaft Sprockets

I just purchased two of the double row camshaft sprockets from Moss and attempted to install one on an engine I am rebuilding. When the nut is tightened, the sprocket is firmly locked to the cam locating plate. Tried two old sprockets (one double row, one single row) and both work properly. Measured the depth of the minor diameter portion of the sprockets which goes through the hole in the cam locating plate. The factory parts measure .148" while the new parts measure .135". The difference of .013" is sufficient to cause the new sprockets to contact the cam locating plate before it contacts the camshaft journal, thus locking up the system.

Moss has been notified, via telephone and a follow up e-mail, of the problem. But, any double row camshaft sprocket is suspect until the problem is corrected.

Les
Les Bengtson

Les,

What was the brand name on those two sets? I just built an engine up a couple months ago and had no problems, but the parts were purchased over the summer. I always check the end-float of the cam plate before putting anything into the block and again afterwards. I use and agree with the recommendations made in Peter Burgess's book for end clearance.

If you bought a new oil pump, be sure to check the ports on it, as the one I had was more than halfway obstructed (casting flaws). I usually port those anyway, but it's good to check if you don't plan to.

Mr. Murphy seems to work overtime when you're working on engines. If you don't check it, that'll be the thing wrong and failure is probably the result...

Sean
Sean Brown

Sean,

My most recent new oil pump was the same as
yours in that it, too, had casting flash in the ports.

Also, the rotor-to-housing cover end clearance
was way over spec. I had to mill the pump body
a bit to tighten up the clearances.
Daniel Wong

Not really related - except in regard to quality of new parts available: I just rebuilt the transmission for my C/GT and the laygear would not go back in because the new needle bearing cages were too wide. Painstakingly, I switched the new needles into the old cages and all is now well. This was in the context of a Twist Transmission Seminar and Moss has been notified.

FWIW,
Allen
Allen Bachelder

I had trouble with this in 1991 when I rebuilt my MGB V series engine. I switched from single to double row sprockets and chain and had the same interference issue. I did some machining to make it work. I think the hub was just plain too long because after cutting down the plate side of the sprocket hub they lined up well. This part was from either Moss or VB but made in India. I guess they didn't use micrometers at that factory. Also they could have been made for Hindustan motors B series which may have drifted in dimensions from the UK engines.

As far as I know all is okay after about 50k+ miles.

Robert McCoy

Sean. The box is marked "Rolon" and it reads "Sprocket for Ambassador Camshaft". There is a stick on, printed label which reads "County" and "Made in India". I have used three of these over the last several years, all of which fit correctly. This batch may be incorrectly machined as Robert's was. Both of my samples measured the same at .135". As Robert suggests, if one has a lathe, the sprocket can be machined to the correct size. A friend has verified that the sprocket can be held in a brake lathe and machined to the correct size. An easier alternative than making an adapter to machine it on my lathe. But, most people do not have their own lathes and may not have a friend with a brake lathe who will machine the part for them for free. Thus, better we get the correctly manufactured parts.

Kelvin Dodd e-mailed me that he will investigate. Either he or I will post a follow up on what they found. I suspect that there are relatively few sources for these parts and, if Moss is having the problem, other sources will be also.

Les
Les Bengtson

Hi Les

Hope you are keeping well? We have been ok so far with the double row rolon sprockets(old stock for me so maybe the new ones are bad). I have had the opposite with the vernier gears...too much play! I use a small surface grinder and magnetic bed to sort the problem. I find it slower but nicer finish to use the grinder. Usually the gears are 12 thou loose.

Peter
peter burgess

This thread was discussed between 04/03/2008 and 06/03/2008

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