Cone ground cam followers

[Mk4Jag]

Hi everybody - new to the forums so still finding my way.
Recently I purchased an aftermarket set of new cam followers for my 1947 pushrod Mk4 Jag only to find that they have been cone ground instead of dome ground. Will these run well on a newly ground cam or will they cause problems?
Regards
Mike.

[Evoluzione]

Try finding your way to Speedtalk and posting there, there is very little in the way of expertise on here these days.

[DVandrews]

I think the profile of the follower is designed to encourage the follower to turn or roll in to the profile rather than being swiped which would accelerate wear. I would consult the supplier. I could ask a good friend who designs cams and followers for a living but the response might be slow.

Dave

[Mk4Jag]

Thanks Dave - would appreciate any help I can get - dont want to damage the cam.
One of the Jag club members had a batch made special several years ago and being just the organiser of the manufacture wouldnt know the technical implications. A cam follower profile machine is a rare beast in the engineering shops these days as most are ground flat for overhead cams. I phoned one engineering shop about getting my old followers ground but he was going to do it with a tool post grinder set over 1.5 degrees that would also result in a cone and not a dome. The cam grinding guy says he will dome them for me at a cost but is he just drumming up unnecessary business?

[DVandrews]

I think the doming is to avoid problems of dig in when the lobe passes the central point of the follower as there will be a loosely defined point. In practice it will very much depend on the profile and the length/width of the flank and any offset of lobe/follower centre that will determine if it is a problem.

Dave

[Mk4Jag]

Thanks Dave. Probably best to let the cam grinding firm grind the followers to suit their cam grind.

[99hjhm]

Tell us who the cam grinding firm is. Have to say, never heard of a concave follower.

There is a debate on A Series(Mini) circles to the radius needed, which on those was convex and is done to make the follower turn.

[Auntieroll]

Ask the cam re/grinding specialists they should be able to tell you the geometry of the lobes and the required follower contact profile.
Radius on followers is usually VERY large ,measured in feet (or metres for the remainers.)
ie near to being flat .
The cam lobes are sometimes ground very slightly tapered to encourage rotation of the follower and thus minimise wear.
A concave follower in an ic engine is in my experience a knackered follower .
IMO the machinist who reckoned on a 1 1/2 degree taper is way out.
1 degree is about 17 thou per inch IIRC which is FAR smaller than the radius required.
The whole cam/follower interface is a minefield of metrology ,design , machining ,heat treatment,lubrication and most , if not all, major manufacturers have encountered problems at one time or another, often related to budgetary constraints .
Special coatings and materials can help resolve competition engine wear problems but are often not economically viable for mass production.
I repeat, valve train design is a complex specialist subject in its own right.

[Mk4Jag]

Hi guys.
When I said cone ground I meant that the follower face was ground with straight sides leading to a conical point at the top centre - not concave which I agree would be a knackered follower. The correct convex curvature is 39" radius which results in an edge relief of about two and a half thou. I think it better to let the cam grinder do his part on them rather than risk the chance of a stuff up.
Thanks for the input guys.
Mike

[Mk4Jag]

Hi guys.
When I said cone ground I meant that the follower face was ground with straight sides leading to a conical point at the top centre - not concave which I agree would be a knackered follower. The correct convex curvature is 39" radius which results in an edge relief of about two and a half thou. I think it better to let the cam grinder do his part on them rather than risk the chance of a stuff up.
Thanks for the input guys.
Mike

[Turn7]

Evoluzione said:

Try finding your way to Speedtalk and posting there, there is very little in the way of expertise on here these days.

I think thats actually a real slap in the face to a number of posters in this area.

I can think of at least 5/6 regulars that are extremely technically minded and very experienced.....

...And happy to offer advice....

Edited by Turn7 on Sunday 15th September 10:03

[Mk4Jag]

Thanks Turn7 - much appreciated.
Regards
Mike

[DeadCatWalking]

You are correct in that the ideal radius of a convex ground pushrod type follower is approx 1 metre. The cam lobe is normally ground with about 2 thou taper from edge to edge to match to this and make the lifter rotate. Cone grinding sounds like a bodge but I'm not saying it wouldn't work. I have refaced worn pushrod type lifters dead flat on my grinder in the past and had no problems and the surfaces end up flat anyway after bedding in and some wear. What I might be tempted to do in your case is take the sharp central point off by giving the lifters a rub on some 180 grit W&D with a little paraffin. I think you'll very quickly end up with a close approximation of a curve ground surface.