HOW WORN IS MY CAM?

[Chimpafrolic]

Hi there,

Today I thought I would have a look at the condition of my cam.

Grateful if the resident cam experts out there (Rob, Spend, Others) would give me their exert opinion on my results.



I guess I have answered my own question with my traffic light colour coding of the results.

However I had expected to see more like 12mm of lift on the thirteen healthy lobes not an average of 10.52mm.


This is my summary of the cam (happy to be corrected though):

• I have thirteen lobes within tolerance

• The greatest range between the thirteen "in tolerance" lobes is 0.94mm (Cyl 6 Exhaust 10.05mm VS Cyl 4 Exhaust 10.99mm) and this would be considered acceptable as they all have over 10mm of lift

• Two lobes (Cyl 5 Inlet 9.66mm & Cyl 2 Inlet 9.81mm) are starting to show the early signs of wear and are likely to rapidly decline due to the onset of lobe hardening failure

• Cyl 3 Exhaust lobe at 6.99mm of lift is worn, and should be considered out of tolerance possibly with most of it's hardening compromised

What I am looking for is someone with good experience of RV8 cam wear to tell me if my above summary is accurate or not.

Having seen snaps of some horrifically worn cams my guess is there are much worse cams than mine still doing service?

The car is a 4.0HC litre Chimaera, the HC spec is supported by the presence of double valve springs and an ECU chip that is clearly marked HC.

My understanding is that the HC was fitted with the TVR435 cam as fitted to the 5.0 litre cars, although again I stand to be corrected on this point.

As stated above I had expected to see more like 12mm of lift on the thirteen healthy lobes not an average of 10.52mm, am I right or wrong to expect this amount of lift on an HC?

Although it's all a bit subjective, given my results the question is:

"HOW WORN IS MY CAM?"

Edited by Chimpafrolic on Sunday 20th February 20:00

[Alexdaredevilz]

Could that not be a shot lifter?

[carsy]

Whats the mileage on it.

[Ant.]

Would not have thought that is a way to make a judegment on your state of cam lift.

Worn lifters, bent push rods are a couple of things that come to mind that may make a difference.

Probably a better measure would be a RR session, or better still pull the cam and inspect.

[Chimpafrolic]

Ant. said:

Would not have thought that is a way to make a judegment on your state of cam lift.

Worn lifters, bent push rods are a couple of things that come to mind that may make a difference.

Probably a better measure would be a RR session, or better still pull the cam and inspect.

• 3.5mm off a lifter would be very unusual in my opinion

• Bent push rods are also pretty rare in my experience and it would have to be bent like a banana to lose 3.5mm

• The RV8 is well known to suffer from cam lobe wear

• Measuring valve lift at the rockers with a DTI is an excepted method of measuring cam wear (well it was when I made my living from wielding spanners)

• It makes absolutely no sense to go to the trouble of pulling the cam just to measure it, if I did that I would simply replace it

Come on chaps, what I am looking for is constructive input from others that have knowledge of what's considered acceptable lift.

I do have a slightly disappointing RR result, I am just trying to diagnose the cause here.

If the cam is considered by those in the know as "not excessively worn" my next step will be to check the cam timing.

As its an HC it should have vernier adjustment, and they are known to slip.

However if the knowledgeable consider it too far out of tolerance then I will likely replace with a MC1.

Calling Rob Robertson.

[spend]

Drain the oil, drop the sump & do a quick visual of the lobes. If it is the cam lobe on that 3 exhaust it will be easy to see. You could lift the valley to see if you're pretty sure it's going to need renewing.

I assume you've checked the rocker shaft for play/wear, felt for excess lash when valve is closed, looked at the rod down the hole....

I think if you log the angles that you begin to see lift and when it's over on each valve may give you better ideas if you just want to do it from the dial indicator. ie just crown of lobe gone or lazy lifting ~ all ends up the same normally though (new set..)

Biggest problem is really that once you have nagging doubts about the cam, it's far easier for piece of mind to just bite the bullet & put your mind at rest

[Chimpafrolic]

spend said:

Drain the oil, drop the sump & do a quick visual of the lobes. If it is the cam lobe on that 3 exhaust it will be easy to see. You could lift the valley to see if you're pretty sure it's going to need renewing.

Good idea, I could do with a new sump gasket anyway

spend said:

I assume you've checked the rocker shaft for play/wear, felt for excess lash when valve is closed, looked at the rod down the hole....

Yes all checked fine

spend said:

I think if you log the angles that you begin to see lift and when it's over on each valve may give you better ideas if you just want to do it from the dial indicator. ie just crown of lobe gone or lazy lifting ~ all ends up the same normally though (new set..)

Also suspecting the vernier sprocket may have slipped

spend said:

Biggest problem is really that once you have nagging doubts about the cam, it's far easier for piece of mind to just bite the bullet & put your mind at rest

Never a truer word spoken, damn your perceptive observations


Thanks Spend, all good points especially the last (sadly)

Calling Rob Robertson again , need to explore my options.

Cant decide if I should do it myself or get the cheque book out?

My back isn't what it used to be

[Ribol]

If the pushrod isn't slapping around all over the place then the cam has to be knackered.

Once it has gone past a certain point it will start to wear fast which is why you have one well ahead of the rest.

[Chimpafrolic]

Ribol said:

If the pushrod isn't slapping around all over the place then the cam has to be knackered.

Once it has gone past a certain point it will start to wear fast which is why you have one well ahead of the rest.

Chimpafrolic said: Cyl 3 Exhaust lobe at 6.99mm of lift is worn, and should be considered out of tolerance possibly with most of it's hardening compromised

I know I am mostly answering my own questions here but it would still be nice to compare my lift figures with a new cam.

The rolling road tells me I am 20% down on HP, which is a lot in my book.

I doubt there would be such a big loss of power from having one exhaust valve opening 30% less and two inlets opening 10% less than the 10.52mm average of the other thirteen valves.

After all there are sixteen valves & eight cylinders.

Unless what I have here is thirteen cam lobes that have all worn at equal rates (unlikely), one knackered lobe and two very much on the way out?

So it would be enormously helpful if someone could tell me if the average lift of 10.52mm on my thirteen valves is normal and within tolerance.

I would have expected something nearer to 12mm based on other engines I have built?

The photos of shot cams I have seen on PH look like the worn lobes would have struggled to lift 3mm, nowhere near the 7mm I am getting even from my worst lobe.

Has anyone got any lift figures taken from a healthy TVR RV8 they can share?

[CarlosV8]

Sorry for the not-very-useful post, but how did you go about measuring the valve lift? What measuring device did you use?

I need to change my rocker cover gaskets and planned to check the valve lift whilst I had it all apart to give me an idea of how healthy my cam is, but not entirely sure how to go about it.

Cheers

Carl

[spend]

Put a DTI on the valve retainers one by one & wind the engine round.

[Chimpafrolic]

I didn't take any photos myself but here are some examples of valve lift being measured in the same way on other OHV push rod engines.







If you measure how much each valve is being opened by it's cam lobe you can establish how worn the lobe is.

A worn lobe will give significantly less lift and should be immediately obvious, look at my exhaust cam lobe on cylinder number 3.

Some variance between the lobes is to be expected and a certain amount of wear can be considered acceptable.

How much wear is acceptable is subjective and is one of the things I am trying to establish here.

My worst lobe is opening it's valve 30% less than the average of the thirteen valves that give very similar lift, I also have two valves that are opening 10% less than this figure.

While my measurements do indicate a my cam is a bit worn I wouldn't mind betting if you took measurements of a cross section of RV8 cams out there mine wouldn't be considered that badly worn.

I doubt its enough to knock 20% off the power output, but I never built an RV8 so I could be wrong?

If you see more or less the same amount of lift at each valve its a good sign the cam is healthy, but its not a guarantee as all lobes may have worn evenly (not that common).

To eliminate even wear across all the lobes we need to establish what lift you should expect from a TVR RV8 with a new cam to make a comparison.

Surely someone must know?????

[Slow M]

If you suspect cam failure, pull the oil filter, cut it open, look for metal particles. You'll know. Best of luck.

Alternate: pull head, pull lifter and visually inspect mating surface.

Also, stop running that motor! You'll be replacing the oil pump as a matter of course if a lobe has failed. If you keep on, potential damage to other components is exacerbated. Have you seen a drop in oil pressure?

B

[Chimpafrolic]

Slow M said:

If you suspect cam failure, pull the oil filter, cut it open, look for metal particles. You'll know. Best of luck.

Alternate: pull head, pull lifter and visually inspect mating surface.

Also, stop running that motor! You'll be replacing the oil pump as a matter of course if a lobe has failed. If you keep on, potential damage to other components is exacerbated. Have you seen a drop in oil pressure?

B

I have seen no drop in oil pressure in he last 10,000 miles, she has always held a solid 30 - 35psi at hot idle on the TVR gauge.

I am reliably informed this translates to a true 55psi if you plumb a decent gauge directly into a gallery and is the correct pressure for an RV8.

I honestly don't see at being that bad, most RV8s have a bit of cam wear and many soldier on for years with some lobes being almost completely rounded.

OK all that metal has to go somewhere, but with regular changes the filtration system seems to be effective enough to allow plenty of old Rangies to march on well in excess of 100k.

With 7mm of lift on my worst valve you could hardly say the lobe is rounded, in fact its still opening a fair bit and it will certainly be allowing the exhaust gasses out (all be it with a bit of restriction).

Being the first to post my valve lift figures here doesn't mean I need to immediately bin the cam, I expect if we all did the same measurements we would be surprised what we would find.

The question is should I bite the bullet like you and Spend have suggested, and slip a new cam in now.

Or wait a while longer & use the money for another trip to the South of France

With the oil and filter changed every 3,000 miles I expect she will happily make it there and back on the old cam, just like it did last year.

These engines are very tough and very tolerant of wear, but do I take your point, the correct thing would be to change the cam.

Its just I don't have an endless supply of cash and the South of France in a TVR does make me so happy

Edited by Chimpafrolic on Monday 21st February 09:50

Edited by Chimpafrolic on Monday 21st February 09:52

[v8 racing]

Hi Dave, your cam lift of around 10.5 mm is about right for a mild cam, the hc engines and 500 ran around the 11.5 mm, if you have one at 6.5 then yes your cam well and truelly shot!, just out of interest when measuring valve lift on the engines you cant do it the way you are doing it to acheive a guaranteed result, the tappets on these engines can leak down very rapidly when you are turning the engine over by hand due to the spring pressure, the only real way to do it is pop all the valve train of and put the dti down the pushrod hole on top of the follower.

[Chimpafrolic]

v8 racing said:

Hi Dave, your cam lift of around 10.5 mm is about right for a mild cam, the hc engines and 500 ran around the 11.5 mm, if you have one at 6.5 then yes your cam well and truelly shot!, just out of interest when measuring valve lift on the engines you cant do it the way you are doing it to acheive a guaranteed result, the tappets on these engines can leak down very rapidly when you are turning the engine over by hand due to the spring pressure, the only real way to do it is pop all the valve train of and put the dti down the pushrod hole on top of the follower.

Many thanks Rob,

I totally understand, 11.5mm is much closer to the 12mm I had in mind and supports my suspicions.

I appreciate my method is a bit flawed with hydraulic lifters, but I was just trying to get a quick indication of what I had expected all along.

Following your response I am now pretty confident it shows my cam to be fooked, so I think its time we talked turkey my friend

Please can you PM me so we can discuss my options.

Cam kit from you & fit myself, or save my poor old back and pay you to do the job for me.

I like the sound of your MC1, if I am honest with myself a lumpy cam with poor idle will just annoy me in the end.

I look forward to hearing from you and thanks again for your advice.

Cheque book at the ready , Dave.

[Chimpafrolic]

Ok chaps,

After all my moaning and bleeting I have just had a chat with Rob and he gets the job.

Nice bloke & excellent advise.

So now its the old MC1 or Stealth chestnut.

Rob advised the Stealth should still give good drivability in my 4.0HC, apparently its the 500s with heavily ported heads that can suffer more low down.

So I am inclined to take the Stealth option and enjoy a bit more top end

Thanks to everyone that chipped in here, especially Spend with his "You know the answer already" post.

And Rob, obviously.

Dave.

[roysum]

Does the HC have pocketed pistons then ?

R

[Chimpafrolic]

roysum said:

Does the HC have pocketed pistons then ?

R

Yup, the 4.0HC ran the same TVR435 cam as the 5.0 litre cars so it does have the valve reliefs machined into the piston crown.

For clarity I discussed all this and a few other points directly with Rob this morning.

Rob had no hesitation in recommending the Stealth as a good option for my 4.0HC, and that's more than good enough for me.

Interestingly I assumed the addition torque of the 5.0litre would help make the Stealth cam smoother at low rpm compared with my little 4.0 litre.

Not so said Rob, in fact he said its the the other way round because of the additional porting work done to the 5.0 litre cars makes them less happy at the lower rev range whatever the cam.

Anyway I am just grateful for Rob's advice, this and his undeniable reputation is why I will be going with the Stealth.

Actually I am feeling much better now I have committed to a new cam, denial can be a dreadful thing.

[roysum]

Chimpafrolic said:

Yup, the 4.0HC ran the same TVR435 cam as the 5.0 litre cars so it does have the valve reliefs machined into the piston crown.

For clarity I discussed all this and a few other points directly with Rob this morning.

Rob had no hesitation in recommending the Stealth as a good option for my 4.0HC, and that's more than good enough for me.

Interestingly I assumed the addition torque of the 5.0litre would help make the Stealth cam smoother at low rpm compared with my little 4.0 litre.

Not so said Rob, in fact he said its the the other way round because of the additional porting work done to the 5.0 litre cars makes them less happy at the lower rev range whatever the cam.

Sweet ! let us know how it goes !

Roy

Anyway I am just grateful for Rob's advice, this and his undeniable reputation is why I will be going with the Stealth.

Actually I am feeling much better now I have committed to a new cam, denial can be a dreadful thing.