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Series A large idler thrust washer



greg brillus

Well Known and Active Website User
VOC Member
#2
Mark I think it is dictated by the oil pump once it is installed, plus if you have a gasket in between or just metal to metal with some sealant. Then from this you can work out how much end float the idler will have.
 

Dinny

Well Known and Active Website User
VOC Member
#3
Greg, thanks for the info. My thoughts are that the thrust washer is the correct thickness to align the large idler with the cam/crank gears and then different thicknesses of gasket are used to set up the end float but I could be wrong?
 

A_HRD

Well Known and Active Website User
VOC Member
#4
Mark,

I'm glad you asked this question because I needed a reason to go searching for mine which went AWOL...

Like most things with the 'A', the answer isn't so easy. Early Singles - yours, and also mine built Oct-Feb 35/36 - had a 2 piece thrust washer comprising a hard steel ring which fitted partially over the bronze bush flange before fitting the assembly in to the crankcase with a 1 to 2 thou interference fit (heat case first -and ensure oil-hole lines up).

Later singles used a one-piece bush (top of pic) to save all the hassle of the earlier variant. This new bush was made from cast iron and had a thicker top-hat brim at 0.218" (same as the earlier steel piece). Let's face it, I don't really see much input to cause any significant longitudinal thrust from the large idler, so this "production easement" must have seemed more logical. Overall length is 15/16", ID is 0.625", OD is 0.8765". Bob S mentions the later variant in "Ab Initio" - which of course is also widely featured in the imminent new book - Back to 'A' (plug, plug). :D

I think you and Greg are both right about idler end-float. It does need some of course, but not much, 4-10 thou max would seem right to me. I don't believe there were ever any figures published for this - but I stand ready to be corrected.

Peter B


large idler bush 001.jpg
 

Dinny

Well Known and Active Website User
VOC Member
#5
Peter,

A picture is worth a thousand words. I was looking for a thin thrust washer not realizing how thick it is. I had it all the time and so I will test assemble the idler/ cam/ oil pump in the next few days and see how much endfloat I have.

Many thanks for the invaluable input, it is very much appreciated.

Thanks
Mark
 

Attachments

Dinny

Well Known and Active Website User
VOC Member
#6
Well, idler is in and when I fit the oil pump (no gasket) it starts to tighten up on the idler. The gasket will give it the endfloat required and I agree, about 5-10 thou should do it. Time to make the gasket...

Thanks
Mark
 

greg brillus

Well Known and Active Website User
VOC Member
#7
Mark, I went through the same process on this Comet and found I had to install a gasket to get some end float on the idler gear. I think from memory it did have a gasket in there as I had kept the remains of some of the gaskets so I could get some idea of their thickness when the reassembly time came about. Cheers..........Greg.
 

Dinny

Well Known and Active Website User
VOC Member
#8
Thanks Greg, I have read somewhere the gasket should be 15 thou so that’s where I will start.
Cheers
Mark
 


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