| Author |
Message |
Paul Newman (Newman)
Junior Member
Username: Newman
Post Number: 164
Registered: 12-2001
| | Posted on Wednesday, May 01, 2002 - 8:41 pm: | |
He was told he had no clearance left on an exhaust valve. What is the shim thickness that is there now? The minimum is 3.25mm. Replace the shim if all else is well. My concern would be what damage will occur, not what power will be lost. |
Brian stewart (Eurocardoc)
Member
Username: Eurocardoc
Post Number: 272
Registered: 11-2001
| | Posted on Sunday, April 28, 2002 - 10:31 pm: | |
What started this line of thought? Did the car suddenly develop a problem, was it after some work being done? It could easily just have one or two bad plug extensions which can cause a popping or similar at that rpm. |
Richard Stephens (Dino2400)
Junior Member
Username: Dino2400
Post Number: 69
Registered: 10-2001
| | Posted on Sunday, April 28, 2002 - 8:15 pm: | |
I don't think you'll lose any power because if it's tight that means it is still going to open just as far as it would if it's set to proper clearance. The problem is that the valve will spend less time on the seat and therefore not have as much time to cool. This may lead to a burnt valve. It may even snap and then chunk up the piston and the head you'll be looking at a lot of work. My dino engine had a snapped valve when I bought so I can attest to the dollars and time required to rebuilt - and you've got a couple of extra cylinders!
In my limited experience, popping and hesitation always turned out to be ignition related and rarely fuel delivery or valve related. But if a tight valve is suspected, by all means take the time to measure the clearances to see. When a head is rebuilt, they often tighten up over time initially (I set my on the loose end of the spec anticipating this). But if the head hasn't been rebuilt and suddenly clearance is lost, then I'm with Edward that something must be wrong with the valve or its seat.
|
Dave328GTB (Hardtop)
Junior Member
Username: Hardtop
Post Number: 117
Registered: 1-2002
| | Posted on Sunday, April 28, 2002 - 7:58 pm: | |
Ken,
For any of us here to guess at how much power you may be down would be sheer speculation. Keep us informed about the final diagnosis and how it is afterwards.
DAve |
Paul Newman (Newman)
Junior Member
Username: Newman
Post Number: 154
Registered: 12-2001
| | Posted on Saturday, April 27, 2002 - 9:40 pm: | |
If you lost your clearance, its either a valve going bad or the seat itself. Should fix it incase something worse comes along = bigger $$$$$ |
Ken Ross (Kdross)
New member
Username: Kdross
Post Number: 31
Registered: 2-2002
| | Posted on Saturday, April 27, 2002 - 8:31 pm: | |
That does not sound good. |
Edward Gault (Irfgt)
Intermediate Member
Username: Irfgt
Post Number: 1230
Registered: 2-2001
| | Posted on Saturday, April 27, 2002 - 8:02 pm: | |
Probably not a huge difference. I still would want to know where the proper clearance went. You just don't loose .030 inches of clearance without something being wrong. |
Ken Ross (Kdross)
New member
Username: Kdross
Post Number: 30
Registered: 2-2002
| | Posted on Saturday, April 27, 2002 - 7:46 pm: | |
I finally brought my car in to have the valves adjusted. As some FC members may recall, my 1985 308 QV was running poorly due to a possible "tight" valve. The car hesitated and "popped" at around 2500 to 3500 rpm. My mechanic is pretty sure that one of the valves is tight and that there is a backwash effect occuring through one of the exhaust valves (hence the popping noise). My question is this, how much more powerful should the car be once the problem is corrected? Should I notice a significant difference in power, or just that the hesitation will be gone? |