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Comet timing chest

Grash

Forum Website User
VOC Member
Advice needed. I am just refurbishing the timing chest and have avidly read all that I can find on fitting spindles, shimming, backlash and a mind boggling amount of other issues. Sometimes I wish I hadn't started... Can someone explain why there is no thrust washer between cam and crankcase. There is much mentioned about side thrust on follower assemblies and I would have thought that some would be transmitted to the cam itself and hence to the case wall.

Thanks

Graham (not an engineer!)
 

Len Matthews

Well Known and Active Forum Website User
VOC Member
Obviously the designers felt that the ground end face of the camshaft abutting the machined surface of the crankcase was sufficient. Anyway, there should not be any end thrust at that point although I agree it is puzzling that shims are interposed between the followers and the crankcase wall but not the camshaft.
 

vince998

Well Known and Active Forum Website User
VOC Member
Cam followers "should" sit flat on the cams with full contact and "should" exert no form of "side" thrust to the cams. Push rods are not always 90° to the followers/rockers and due to followers and rockers moving in a 90° opposed arc to each other(thats why the push rods have balls on the ends and the followers/rockers have cups), some side thrust will be generated.
Obviously the designers felt that the ground end face of the camshaft abutting the machined surface of the crankcase was sufficient. Anyway, there should not be any end thrust at that point although I agree it is puzzling that shims are interposed between the followers and the crankcase wall but not the camshaft.
 

vince998

Well Known and Active Forum Website User
VOC Member
Something else to watch out for is that the holes in the steady plate are not countersunk. Not so much of a problem on comets as they are made of steel and aren´t subjected to over-exhuberant fettling, but i´ve seen new steady plates for twins with this strange practice. Has the effect of dishing the shims over the end of your spindles (especially the cam follower spindles) when tightened, and totally buggering up your painstakeingly set running clearances.
Advice needed. I am just refurbishing the timing chest and have avidly read all that I can find on fitting spindles, shimming, backlash and a mind boggling amount of other issues. Sometimes I wish I hadn't started... Can someone explain why there is no thrust washer between cam and crankcase. There is much mentioned about side thrust on follower assemblies and I would have thought that some would be transmitted to the cam itself and hence to the case wall.

Thanks

Graham (not an engineer!)
 

chankly bore

Well Known and Active Forum Website User
Non-VOC Member
I am assuming you are fitting steel large and small idler gears, and are aware of the errors in Richardson re cam timing and thrust washer location. Join the Club. There will be someone local who can help you. F5AB/2A/7945 since 1970
 

greg brillus

Well Known and Active Forum Website User
VOC Member
All the timing gears are straight cut gears meaning no end thrust loads, forget about the exact amount or thickness of shim washers either side of the followers but rather use shims to align the face of the follower with the width of each cam lobe to minimise wear....take your time and set each up carefully...it will be worth it, cheers....Greg.
 

Grash

Forum Website User
VOC Member
Thanks for the tips guys (by the way I am a member, dont know why it says I'm not, 21310AA). I've hit my first problem, getting the new follower spindles in. Heated the case to 200C ("No dear, nothing's burning"), Tight going in, became very tight then stopped. Took them out again and there is a clear ridge showing, half way in but only on one side. Thought I had it straight but perhaps not. Think I'll stop tonight before I do any more damage.

Cheers
Graham
 

greg brillus

Well Known and Active Forum Website User
VOC Member
Are the spindles you are fitting the same thickness over their total length or do they have a small step about 20mm from the inboard end, in other words...you could be installing oversize spindles without realising it, which would explain what you are describing. If you have the case at @ 200 celcius they shouldn't be that tight to install. Should also use a piece of tube machined to the correct length and slipped over the spindle to act as a limit stop whilst using washers as packers and a plain 5/16 BSF nut just proud of the end of the spindle so as not to hit the end of it...then tap the spindle into it's hole....once they are home you don't want to be adjusting them again soon....cheers....Greg.
 

Grash

Forum Website User
VOC Member
Thanks for the tip but the new spindles are 0.375" all the way. I'm very limited on equipment (verniers, drill press and assortment of hammers) but as best as I can, the bottom half of the hole ie the bit I've not yet wrecked, measures 0.370. I dont know the exact material, but most engine alloys are listed having coeff of expansion of around 20 x 10^-6. At 0.375 diameter and a rise of 180 degs, this will give a change of approx 1.3 thou diameter. This means I still have an interference of 3+ thou. I suppose as soon as the spindle starts to warm up (which prob wont take very long), this will change. I need someone to tell me what such a fit feels like. Do I need to "ease" something?

BTW Vince998, had a look at the steady plate for countersinking and it didnt look too bad, but the shoulders of the new spindles are chamfered or filletted or whatever the term is, for almost half of the radial width of the edge. Presumably this is not good?

Cheers
Graham
 

vince998

Well Known and Active Forum Website User
VOC Member
Hi Grash,
As long as the timing plate holes are not countersunk, the tapers on the spindles won´t cause the shims (ET98/1) to dish.
To aid fitting spindles, assemble the spindle together with cam or follower and 1 extra shim (E95(cam) or ET98(follower) + nuts and put in the freezer overnight.
Heat cases to 200°c for a good couple of hours, carry out to garage or down to cellar where your spindle assys are waiting in a coolbox. Tap each spindle assy into place (it really should only need a tap).
After the last spindle is in place, remove the nuts (starting with the first spindle, it should have heated up enough to be gripped by the crankcase), and leave to cool.
As the cases cool, they retract the spindles in a little, but you´ve calculated for this by using an extra shim.
If everything is as it should be (all assembly are exactly the same width on the spindles, you´ve cracked it. If not, now comes the task of lining up the spindle ends so that the steady plate pulls down flush and at the same time enough clearance for the various components is present. (Your´re lucky, you only have 3 spindles to match up ;-)
Leave this until the crankcase halves are back together and done up tight!!!
Don´t worry if you have to pull out spindles a little to line up the ends (ends of the spindle shafts and not the threads) using a slide hammer, you can compensate with shims to attain correct clearance (thats why shims are there so use them!!). I´ve even put extra shims behind the followers to get them full contact with the cam before.
If done properly, you shouldn´t have to touch the timing side again for a long time.
On assembling, it is very easy to pinch the E95 shim/s between the spindle end and the steady plate (falls off the spindle and onto the threaded portion). Use clean oil for assembly and look before nipping everything up.
Thanks for the tip but the new spindles are 0.375" all the way. I'm very limited on equipment (verniers, drill press and assortment of hammers) but as best as I can, the bottom half of the hole ie the bit I've not yet wrecked, measures 0.370. I dont know the exact material, but most engine alloys are listed having coeff of expansion of around 20 x 10^-6. At 0.375 diameter and a rise of 180 degs, this will give a change of approx 1.3 thou diameter. This means I still have an interference of 3+ thou. I suppose as soon as the spindle starts to warm up (which prob wont take very long), this will change. I need someone to tell me what such a fit feels like. Do I need to "ease" something?

BTW Vince998, had a look at the steady plate for countersinking and it didnt look too bad, but the shoulders of the new spindles are chamfered or filletted or whatever the term is, for almost half of the radial width of the edge. Presumably this is not good?

Cheers
Graham
 
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