Thread: Lumpy Cams and Valves

Did a broken spring cause the valve to drop or did the collet let go.

A wilder cam generally has more lift and duration which has the valve spring under higher compression for longer. It could also bend or break the rocker arms.

I would say the failure is related to the cam change.

In racing most people make 1 change at a time to see whether that change makes things better or worse.

James

Havn't had a chance to take the rocker cover off, I think I might be trying to make some room in the shed to do the work on it myself from now on though, especially if he's going to be denying stuff and thinking he can just keep charging us for stuff that is his fault.

Shamo

'dropping' a valve and burning out a valve are two very different things. 'Dropping' a valve refers to the collets that hold the valve in place failing, leading to the valve falling into the cylinder and causing catastrophic damage. a burnt-out valve is where the valve seat is eroded by the combustion gases leaking past it, due to not fully seating or a worn seat developing a leak. Either one could result from other valve train work, but I think it is a bit harsh to hold the guy responsible for engine issues that occur on a race car. May or may not be caused by the lumpier camshaft, 'post hoc ergo proctor hoc'.

Originally Posted by POD

but I think it is a bit harsh to hold the guy responsible for engine issues that occur on a race car.

x2 ....

Cheers
Mike

hi
i agree that it is a little harsh to blame your engine builder at least without knowing what has actually happened. i do find it an issue the he changed something (anything) on the car with out you knowing, unless you have an agreement with him where he can do what he deems best. a race cam wil put alot more stress on related parts but you do have to ask yourself if the guy had asked you before would you have said yes to the extra power the cam cam shaft can give!!
hope you get this sorted
BT

Couple of thoughts here...

First, Camshafts are the one component that needs the most attention when running in, particularly in a race engine. Did you get any instructions? Did you follow them?

Second, a more lumpy cam will compress the power band & move it higher in the rev range. Did you use those extra revs? And... were valve springs, followers etc changed to suit? It's possible you got valve float & that's when it let go.

The carbs, manifolds & ports, valves & cam, pistons, CR etc all need to be matched. If anything is below spec or not up to the job you'll get poor times or failure.

Been there many many times...

Regards
Max P

Did he build the engine and choose all the new components originally? If he did then he should know how much valve to piston gap there is.

You can also get valve spring binding if the cam is to big, when this happens the damage is usually massive.

You say it has longer rods and different pistons. Do the new pistons have the same deck height as the standard pistons or not? If the deck height is the same as the standard piston but a longer rod has been fitted then the piston tops out higher then standard which would mean the dome of the piston sits closer to the valves.

Before fitting a higher lift cam a good performance engine builder would take the head off put plastercene or similar on top of the piston bolt the head back on with the old head gasket and the new cam fitted and with the cam timing he intends to run dialed in, then turn the engine over by hand. Then remove the head and see if there is a reasonable valve to piston gap by measuring how thick the palstercene is that is left where the valve has pushed into it when opened.

Then and only then would he know if there is enough piston to valve clearance for the new cam. This is a very time consuming job and one that few mechanics know how to do properly.

Anyway good luck with this but its quite possible from what you have said that a mistake might have been made. The only way to find out is to strip the engine and see what is bent and broken.

Now can anyone please tell me if TDV6 injectors can be serviced and cleaned successfully?

cheers,
Terry

Originally Posted by POD

but I think it is a bit harsh to hold the guy responsible for engine issues that occur on a race car. .

Originally Posted by Brit Tech

hi
i agree that it is a little harsh to blame your engine builder at least without knowing what has actually happened. i do find it an issue the he changed something (anything) on the car with out you knowing, unless you have an agreement with him where he can do what he deems best. a race cam wil put alot more stress on related parts but you do have to ask yourself if the guy had asked you before would you have said yes to the extra power the cam cam shaft can give!!
hope you get this sorted
BT

I agree, I think I may have been expressing myself in a slightly frustrated/stressed way the other night and probably blamed him for alot more than was his fault.

Originally Posted by Tusker

Couple of thoughts here...

First, Camshafts are the one component that needs the most attention when running in, particularly in a race engine. Did you get any instructions? Did you follow them?

Second, a more lumpy cam will compress the power band & move it higher in the rev range. Did you use those extra revs? And... were valve springs, followers etc changed to suit? It's possible you got valve float & that's when it let go.

The carbs, manifolds & ports, valves & cam, pistons, CR etc all need to be matched. If anything is below spec or not up to the job you'll get poor times or failure.

Been there many many times...

Regards
Max P

No instructions were given from him, he just told me it should be making more power than last time (which the few times i got to post did reflect) and yes I was using the full rev range...

Originally Posted by TerryO

Did he build the engine and choose all the new components originally? If he did then he should know how much valve to piston gap there is.

Yes he built the whole engine and has done heaps of escorts before so I'm sure he knew what parts he was using and how much clearance there will be etc. (this backing up the fact that I probably shouldn't be blaming him for as much as I had originally)

All in all, I agree, no real assumptions can be made until the engine itself is stripped and assessed. This of course will be the next thing we do and will go from there. This thread was more just to gauge a bit of a general feel about whether or not there is a direct correlation between the two that would have been more obvious than having to pull the engine down.

Cheers for the replies guys, will keep you posted.

Shamo