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cam replacement

redbloke1956

Well Known and Active Forum Website User
Non-VOC Member
Hi to all, I have just received my new Mk 3 cams and cam followers for my Comet and have a few questions
1 to press the old cam out of its gear should I heat the gear first ?
2 is there a trick to lining up the gear and new cam positions prior to assembly ?
3 can/should the pushrods ends be tempered so that they can shape themselves to the seats in the new followers ?
Any hints/tips or further advice appreciated.
Thanks
Kevin
 

Len Matthews

Well Known and Active Forum Website User
VOC Member
No need to heat the cam pinion. To enusure you press the pinion on to your new camshaft in the right position, note there is (or should be) a notch in the end face of the cam. This was used to locate the cam in the Factory jig so that the timing marks were in the right place. Without this jig you can, before pressing out the worn cam, scribe two lines parallel with the notch on the face of the pinion. This will give a guide when pressing in the new cam. Try to get it right first time because too many attempts will spoil the interference fit.
Assuming you have stainless push rods, no tempering is necessary but it's wise to ensure they can spin freely in the followers and the rocker adjusters. Lapping the ball ends with fine grinding paste is worth doing but make sure all traces are removed afterwards.
 

davidd

Well Known and Active Forum Website User
VOC Member
Follow Len's advice! The timing details are in Instruction Sheet no. 6, I believe, but Len's method obviates the need for the details. Getting the marks right is only important for timing the gears the next time the chest is apart. If you press it in yourself you need to check and probably adjust the timing. Some would say that is necessary even with the cam supplied with the pinion pushed on.

In general, the pushrod ends do not match well and for best results you should shape them to the followers and adjusters. You can do it with paste, I use the oil soluble paste. A Vincent man told me recently to chuck the push rod in the drill press and use a cam follower to shape it on low speed with some paste. You can do it without paste by using a diamond stone and just checking for the high spots visually with some magnafication. Keep shaping the shiny spots (high spots) until it is all shiny.

This cam indexer was copied from a photo of one used at Harpers, I believe, from Peter Barker. It has two fixed pins (inner and outer) and the one in the middle is spring loaded and disappears in the base. This latter pin engages with the groove in the cam and the outer pin locates the gear in the propper relationship to the gear teeth. You can simply place a correctly indexed cam on the base and mark where the dots should be, lining up the new pinion on those marks. It may be difficult to see, but I have a Comet mark on the left side of the base.

David

CamIndexJig.jpg
 

nkt267

Well Known and Active Forum Website User
VOC Member
Also be aware that if the interference fit on the new cam to cam wheel is to small then the cam can turn in the cam wheel. Gary Robinson tack welded both the cam assemblies I sent him to stop this happening..John
 

davidd

Well Known and Active Forum Website User
VOC Member
Spot welding in good, but not always necessary if the pinion and gear are good. If welded, the spot weld needs to be tidy and ground afterwards so there is no interference with the steady plate and washers.

David
 

clevtrev

Well Known and Active Forum Website User
VOC Member
Spot welding in good, but not always necessary if the pinion and gear are good. If welded, the spot weld needs to be tidy and ground afterwards so there is no interference with the steady plate and washers.

David

One does NOT weld on that side, simply because when, the next time you remove the shaft, it buggers up the hole.
 

clevtrev

Well Known and Active Forum Website User
VOC Member
Spot welding in good, but not always necessary if the pinion and gear are good. If welded, the spot weld needs to be tidy and ground afterwards so there is no interference with the steady plate and washers.

David

One does NOT weld on that side, simply because when, the next time you remove the shaft, it buggers up the hole.
 

davidd

Well Known and Active Forum Website User
VOC Member
I have never welded a pinion to a shaft, but all the ones that have been provided to me have been done on the outside, including the Robinson cams. It is a very good point. I do not spot weld them for that very reason. So far, so good.

David
 
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