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MG Midget and Sprite Technical - Camshaft Thrust Plate

Can anyone tell me how thick a new camshaft thrust plate should be? I wonder whether the new supplies are coming in too thin as I have about 15 thou float. The plate is about 2.35mm (about 95 thou). Doesn't look to have white metal on one side either.
Graeme Williams

Correction to the above - it does have white metal one side (cam side). Wonder why they only coat one side since both sides are working as thrust faces?

That sprocket has done 15000 miles AFAIK so has it always had excessive end float I wonder?


Graeme Williams

Now looks like the problem is a badly made sprocket where the step has been machined 10 thou too deep.
Graeme Williams

I can measure one tomorrow - unless the details are somewhere in the archives in Lawrence's 'oil sucking' thread.

I bought a new plate from Minispares when I was building my A35 engine (1987) and it was too thick, so the camshaft wasn't rotating freely. I ended up using the original.

I do have some genuine Rover NOS plates in the garage.
Dave O'Neill 2

Could you correct the float with 0.01" shimstock in the recess? (Don't know if that's a daft comment or not, I don't have one to hand to look at).

On the other hand Haynes suggests there are cam float adjusting shims of 0.004" and 0.006" for the sprocket - are they still available?
Greybeard

You need to machine some off the back of the sprocket to reduce the endfloat.

The plate is only white metalled on the cam side because the cam is pushed forward by the oil pump/dizzy drive and therefore it is not in contact with the front side of the plate.
Chris at Octarine Services

I've measured four NOS plates at various points:-

No.1 was 2.28 - 2.30mm

Nos 2 & 3 were 2.28 - 2.31mm

No 4 was 2.28 - 2.32mm

Approx .090 to .091"
Dave O'Neill 2

A little adjustment with a file and all is now well. Engine almost ready for placing back in Graemes car when I get time next week.
Alan
Alan Anstead

Dont use haynes shop manual for this...

haynes has the wrong specs (typo?) for the end float ect ect ..i dont remember the details but use a differsnt manual (bently) for this spec
1 Paper

I dont possess a Haynes for a Spridget.
Alan Anstead

Interesting. What should the endfloat be? My Haynes says 3 to 7 thou for A series (which looks reasonable to me), but from 4 and a half thou to 85 thou for the 1500, which does indeed look like a typo. A missing "0" perhaps.

If someone wouldn't mind posting correct values I'd like to make the correction. Thanks.
Greybeard

Thanks for everyone's comments. As Alan says the sprocket as fitted had too large a step where it engaged on the end of the camshaft, so "we" filed off 10 thou and now have 5 thou end-float. What is disconcerting is that this sprocket has been fitted by the po for 15000 miles and running with 15 thou float.

Ready made shim washer are stock items but are sized to fit the crankshaft to align the two sprockets so the chain doesn't run out of line.
Graeme Williams

Just a picture.

Alan Anstead

I build A and B series to 1.5 to 2 thou" end float cam shaft and 3-4 thou" crank end float.
I have also found many builders, amateur or pro, do not measure the end floats and they also tend to put the cam in 'on the dots'
Peter
Peter Burgess Tuning

While we were trying to resolve the endfloat issue Alan and I swapped the timing gears for an old set Alan had. When we degreed the cam the timing was around 3 degrees different from the original set. As we didn't have an offset key to hand we reverted to the original gears and a spot of enthusiastic filing.
Just goes to show how much variation you can get with dot to dot.
Graeme Williams

Graeme,

It depends on the accuracy of machining of the keyway - I have found sprockets of both the double and single varieties having several degrees difference between them.

Just underlines that you can assume nothing and have to measure and "fit" parts whether old or new.
Chris at Octarine Services

I wonder Chris, are the "dots" punched on when the wheels are fitted to an engine, or just stamped at time of manufacture?
Graeme Williams

I don't think it really matters how accurately the dots are placed, as
long as they are in the general vicinity of where they should be. The important thing is that the keyways are machined accurately in relation to the gear teeth.

As there are two gears, each with a keyway, they need to be machined very accurately.
Dave O'Neill 2

Dots or sometimes raised marks are made with the sprockets but I guess there are manufacturing tolerances which allow things to wander a bit.

Also the machining of the camshaft & crank could be out slightly - especially if the cam has been reground at some time.

In the production environment they may have selectively chosen parts so that tolerances cancelled out - or they may have just thrown them together - who knows?

Offset keys are the answer to timing the cam correctly - the vernier sprockets are an expensive way of doing the same thing!
Chris at Octarine Services

This thread was discussed between 08/05/2017 and 13/05/2017

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