Is there a fault with this camshaft?
Discussion
I'm rebuilding a pre-war Riley special -the engine was half done when I bought it, with all the bottom end assembled. I'm a bit worried about what I see when I look through the fuel pump mounting aperture to one of the camshafts. On the picture, you can see two cams with their followers above sitting on the base circle, with the fuel pump eccentric between.
Now, I was told that the engine had "fast road" cams fitted, and it looks to me as if the camshaft has been reground to give more lift (and presumably duration) by reducing the base circle diameter. However, on the cam on the right it looks like the base circle has been reduced below the diameter of the adjacent shaft, leaving a step, but the follower is of large enough diameter to be sitting on the step, not the base circle. I'm thinking this means it will be impossible to set valve clearances correctly, and the follower wil get an almighty smack when the opening ramp hits it.
So, I'm fearing that I should strip the bottom end to get the camshafts out, check them properly and if necessary get them corrected. What's the PH collective wisdom -anyone seen anything like this before?
Now, I was told that the engine had "fast road" cams fitted, and it looks to me as if the camshaft has been reground to give more lift (and presumably duration) by reducing the base circle diameter. However, on the cam on the right it looks like the base circle has been reduced below the diameter of the adjacent shaft, leaving a step, but the follower is of large enough diameter to be sitting on the step, not the base circle. I'm thinking this means it will be impossible to set valve clearances correctly, and the follower wil get an almighty smack when the opening ramp hits it.
So, I'm fearing that I should strip the bottom end to get the camshafts out, check them properly and if necessary get them corrected. What's the PH collective wisdom -anyone seen anything like this before?
I can't see enough detail in the photo but if it is as you say then certainly the cam needs sorting as it won't run like that. Nice spot btw. Not many people would have noticed that.
Cams should have a substantial undercut each side of the lobe and no regrind should use all of that up. This makes me wonder if the regrind has gone right through any hardening involved although I have no idea what cam metallurgy an engine like yours uses. Modern cams are mainly chill-cast grade 17 iron which generates very hard carbides in the iron during the casting process but old pushrod cams tend to be either flame or induction hardened cast iron, induction hardened carbon steel or as with the Leyland A and B series a type of steel such as EN34 which work hardens against the follower during the running in period.
Probably best to try and compare it with a stock cam to see how much has been taken off. The cam grinder must not have been the sharpest tool in the box to have done a job like that which also makes one wonder if the new lobe profile is even vaguely suitable for the engine.
Cams should have a substantial undercut each side of the lobe and no regrind should use all of that up. This makes me wonder if the regrind has gone right through any hardening involved although I have no idea what cam metallurgy an engine like yours uses. Modern cams are mainly chill-cast grade 17 iron which generates very hard carbides in the iron during the casting process but old pushrod cams tend to be either flame or induction hardened cast iron, induction hardened carbon steel or as with the Leyland A and B series a type of steel such as EN34 which work hardens against the follower during the running in period.
Probably best to try and compare it with a stock cam to see how much has been taken off. The cam grinder must not have been the sharpest tool in the box to have done a job like that which also makes one wonder if the new lobe profile is even vaguely suitable for the engine.
Looks to me as though the step is in the right direction, i.e. surface to the left of the lobe is lower than base circle. Would be easy to check the direction of the lip with a probe (e.g screwdriver) through the hole you took the picture through. Admittedly, it looks like the base circle has been reduced to the absolute max.
Pumaracing said:
I can't see enough detail in the photo but if it is as you say then certainly the cam needs sorting as it won't run like that. Nice spot btw. Not many people would have noticed that.
Thanks! I've just turned the engine over and looked a little closer, and the adjacent lobe is even worse -it's being held nearly 1mm off the base circle!Pumaracing said:
Cams should have a substantial undercut each side of the lobe and no regrind should use all of that up. This makes me wonder if the regrind has gone right through any hardening involved although I have no idea what cam metallurgy an engine like yours uses. Modern cams are mainly chill-cast grade 17 iron which generates very hard carbides in the iron during the casting process but old pushrod cams tend to be either flame or induction hardened cast iron, induction hardened carbon steel or as with the Leyland A and B series a type of steel such as EN34 which work hardens against the follower during the running in period.
As far as I can tell all the surfaces I can reach are still hard, using a crude "try and scratch it with a screwdriver" test.Pumaracing said:
Probably best to try and compare it with a stock cam to see how much has been taken off. The cam grinder must not have been the sharpest tool in the box to have done a job like that which also makes one wonder if the new lobe profile is even vaguely suitable for the engine.
Who knows! However, it will cetainly need to come out and go back to a cam grinder. Any recommendations for someone who knows what they're doing?BTW, I'd just like to sat how much I value Pumaracing's contributions to this forum.
If the lobe profile is ok and all you need to do is put an undercut each side of the lobes then that's a fairly simple op with a carbide tool or an abrasive wheel grinder which many engineering shops could do. Now I could evaluate the profile for you if I explained to you how to measure it properly with a dial gauge and degree wheel but it's time consuming and it might be easier to just speak to people who really know their stuff like Dave and his son at Newman Cams and let them do the whole thing.
http://www.newman-cams.com/contact.html
Tell them I sent you. They'll be able to measure the profile and will probably even know what the OE one is. If the profile now on there is not too radical for road use and the compression ratio of the engine (which might benefit from being increased) and is also correctly designed to match the follower diameter (which they'll need to know) then they can machine the undercuts in, chamfer off any sharp edges and the job's a good'un.
However I have my concerns about both the amount that's been taken off and also whether the profile now copied onto this cam is from a suitable and similar engine. I suspect it'll just be a profile from another common pushrod engine like a Mini, Ford Crossflow or whatever and if the follower diameter is different from yours then it might not work properly for technical reasons which I won't go into here. Dave and his son will understand all this in great detail and will be able to tell you if it's salvageable or scrap and you need a new cam.
They might also need to know which side of the lobe the followers sit on (they should be offset by a few mm from the lobe centreline) and what the lobe taper angle is to spin the follower properly. They'll already know all this if they've dealt with this type of engine before but they'll tell you what they need you to send them and any measurements you might need to take.
If the only solution is yet another light regrind then the followers will need replacing or refacing if they are not already new ones. Dave might be able to reface them so I'd also ask him this. In fact point him at this thread or email him my post and they'll see what the issues are.
http://www.newman-cams.com/contact.html
Tell them I sent you. They'll be able to measure the profile and will probably even know what the OE one is. If the profile now on there is not too radical for road use and the compression ratio of the engine (which might benefit from being increased) and is also correctly designed to match the follower diameter (which they'll need to know) then they can machine the undercuts in, chamfer off any sharp edges and the job's a good'un.
However I have my concerns about both the amount that's been taken off and also whether the profile now copied onto this cam is from a suitable and similar engine. I suspect it'll just be a profile from another common pushrod engine like a Mini, Ford Crossflow or whatever and if the follower diameter is different from yours then it might not work properly for technical reasons which I won't go into here. Dave and his son will understand all this in great detail and will be able to tell you if it's salvageable or scrap and you need a new cam.
They might also need to know which side of the lobe the followers sit on (they should be offset by a few mm from the lobe centreline) and what the lobe taper angle is to spin the follower properly. They'll already know all this if they've dealt with this type of engine before but they'll tell you what they need you to send them and any measurements you might need to take.
If the only solution is yet another light regrind then the followers will need replacing or refacing if they are not already new ones. Dave might be able to reface them so I'd also ask him this. In fact point him at this thread or email him my post and they'll see what the issues are.
Edited by Pumaracing on Sunday 23 October 17:47
Pumaracing said:
If the lobe profile is ok and all you need to do is put an undercut each side of the lobes then that's a fairly simple op with a carbide tool or an abrasive wheel grinder which many engineering shops could do. Now I could evaluate the profile for you if I explained to you how to measure it properly with a dial gauge and degree wheel but it's time consuming and it might be easier to just speak to people who really know their stuff like Dave and his son at Newman Cams and let them do the whole thing.
http://www.newman-cams.com/contact.html
Tell them I sent you. They'll be able to measure the profile and will probably even know what the OE one is. If the profile now on there is not too radical for road use and the compression ratio of the engine (which might benefit from being increased) and is also correctly designed to match the follower diameter (which they'll need to know) then they can machine the undercuts in, chamfer off any sharp edges and the job's a good'un.
Thanks, I've spoken to Newman Cams, and they will take a look at them. They are familiar with the engine, and actually have a new pair of camshafts on the shelf if the worst comes to the worst!http://www.newman-cams.com/contact.html
Tell them I sent you. They'll be able to measure the profile and will probably even know what the OE one is. If the profile now on there is not too radical for road use and the compression ratio of the engine (which might benefit from being increased) and is also correctly designed to match the follower diameter (which they'll need to know) then they can machine the undercuts in, chamfer off any sharp edges and the job's a good'un.
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