How do you tell if the cam is knackered ??
Discussion
..is it obvious ? My chim has always had a v.slight engine ticking noise - not very loud at all ( def not exhaust manifold) and it still pulls very strongly. But at the last service (40K) it was mentioned that I will probably be looking at a new cam soon as "they all go about 40-50K"...is this the case does anyone still have the original cam at 60K, 80K ??? and what are the tell tale signs to look for when it about to go or has gone ???
I don't know about the anecdotal signs particular to your car, but in general you inspect them.
Usual signs are uneven wear on the cam lobes. If the follower doesn't sit all the way across the lobe, it's common to find wear where the follower interfaces.
If this is the case you can measure the size of the step. If the follower sits right across the lobe, it may not be possible to observe wear in this way.
Then, the only way is to put the shaft up between centres, with a dial guage running from the lobe. You can then measure each of the lobes against a spec table that shows deflection versus angle.
Further thought suggests that you might be able to get the overall open to closed dimension for each of the lobes and mic up the cam for comparison.
>> Edited by dilbert on Monday 7th March 12:47
Usual signs are uneven wear on the cam lobes. If the follower doesn't sit all the way across the lobe, it's common to find wear where the follower interfaces.
If this is the case you can measure the size of the step. If the follower sits right across the lobe, it may not be possible to observe wear in this way.
Then, the only way is to put the shaft up between centres, with a dial guage running from the lobe. You can then measure each of the lobes against a spec table that shows deflection versus angle.
Further thought suggests that you might be able to get the overall open to closed dimension for each of the lobes and mic up the cam for comparison.
>> Edited by dilbert on Monday 7th March 12:47
From my own experience, my car had flat 'spot' over 4000rpm, with lots of popping and banging to accompany it, with an apparent breathlessness. I took it to Noble's in chesterfield, who examined the engine externally, ran some tests etc but could not find anything specific wrong with it. They said then that it was probably the cam, but would need to open it up to be sure.
Cue searches on PH and an expensive trip to coventry (TVR Power). Camshaft was deemed 'scrap', and ended up having complete 'Taraka' upgrade.
Very worth it. oh
Cue searches on PH and an expensive trip to coventry (TVR Power). Camshaft was deemed 'scrap', and ended up having complete 'Taraka' upgrade.
Very worth it. oh
On mine, they shone an infra red heat sensor thingy onto each branch of the exhaust manifold as close as they could to the head. The differences in temprature showed that 2 or 3 cylinders were not working to their full potential, they said most likely cause was the cam, they were right.
If you have rolling road figures, low power with high torque is also a clue, apparantly, although not definitive.
Don't rule out the exhaust manifold / gasket either... it is a metallic tick! If the heat sensor thingy indicates no internal probs, look there.
If you have rolling road figures, low power with high torque is also a clue, apparantly, although not definitive.
Don't rule out the exhaust manifold / gasket either... it is a metallic tick! If the heat sensor thingy indicates no internal probs, look there.
deeen said:I've found it very difficult to get clear results from this. Might work better if you can do it on a rolling road, but an engine just ticking over seems to have quite big variations in header temperatures from cylinder to cylinder. Think it may be something to do with the very unequal header lengths on these engines.
On mine, they shone an infra red heat sensor thingy onto each branch of the exhaust manifold as close as they could to the head.
I think you might be able to guess at the problem if you have an unexpected power loss or rough running at high rpm, and if the cam is so far gone that some lobes are completely gone you could in principle collapse the lifters and measure the valve clearances. But I think in practice the only way to be sure is to take the valley gasket off and actually inspect it.
Rough and ready test (you don't need a fancy meter for this). Take the car out one dark evening and find an area free of ambient light to stop in. Pop bonnet and get tracy to hold the revs at 2k-2.5k. Have a look at the pipes - they'll be glowing. If there's a noticeable difference in colour between the pipes this may indicate an issue. Mines heading for 62k and is a little noisy, but nothing outrageous. I'm expecting I need to change the cam at some point, likely before LM, but am holding off for now.
Steve.
Steve.
Mines on over 100k now and I suspect mine is due for a change. From what I can tell it's still the original.
Car is still running OK, but seems to be a little slower getting up into the higher revs than it used to be (bought the car on about 65k). Seems to have trouble getting above 5000 sometimes!
Also as mentioned above, lots of pops and bangs!!
Anyone got a rough idea how much to replace one including labour. (cue the cries of dispear!!)
Car is still running OK, but seems to be a little slower getting up into the higher revs than it used to be (bought the car on about 65k). Seems to have trouble getting above 5000 sometimes!
Also as mentioned above, lots of pops and bangs!!
Anyone got a rough idea how much to replace one including labour. (cue the cries of dispear!!)
Hi Snorky - forgot to say 68000 miles for me. And a small exhaust manifold / gasket blow is still a very metallic tick, btw!
Hi GreenV8S - I drove 80 miles to the garage and he jumped straight out and shone the thingy at it, might this have helped? Inconclusive, hmm, you may have a point (you usually do!) well he didn't spot the other internal problem till he got it apart(head gasket blowing between 2 cylinders) and the third cylinder with a low reading, although not as low as those two, I couldn't see (quick glance with the naked eye) a problem with the lobes on the old cam he showed me.
Hi Dilbert. AFAICS, the cam lobes bear on the centre of a hydraulic tappet with a large flat face, so no step. However, on mine, two of the lobes were visibly gone, no need for measurements when it was that far gone! Assuming the old cam I was shown was actually the one from my car, of course.
Not my usual garage, in case anyone who knows me is not in the pub yet.
Hi GreenV8S - I drove 80 miles to the garage and he jumped straight out and shone the thingy at it, might this have helped? Inconclusive, hmm, you may have a point (you usually do!) well he didn't spot the other internal problem till he got it apart(head gasket blowing between 2 cylinders) and the third cylinder with a low reading, although not as low as those two, I couldn't see (quick glance with the naked eye) a problem with the lobes on the old cam he showed me.
Hi Dilbert. AFAICS, the cam lobes bear on the centre of a hydraulic tappet with a large flat face, so no step. However, on mine, two of the lobes were visibly gone, no need for measurements when it was that far gone! Assuming the old cam I was shown was actually the one from my car, of course.
Not my usual garage, in case anyone who knows me is not in the pub yet.
Worth checking the rockers as well. The bible shows some pretty piccies of what can go wrong and the resulting damage. The cost is dependent on whether it is just the cam or other bits like rockers need to be done.
No reliable way except inspection but valve lift and compression testing along with the other less reliable stuff can help to build a picture of what is going on.
No reliable way except inspection but valve lift and compression testing along with the other less reliable stuff can help to build a picture of what is going on.
Gassing Station | Chimaera | Top of Page | What's New | My Stuff