When to Rebuild Cylinder Head

[DG624]

I have an 86 Carrera with about 135,000 and am going to add some exhaust and intake improvements to boost HP but should I have the cylinder heads rebuilt to make these changes effective and make sure the engine is working at the prescribed level?

I think the valve springs should be replaced but will a simple leakdown test show valve and valve seat condition?

[Flat6pac]

At 135K you need head work, studs and springs are the least..You ll be suprised how well things work with a valve job. The leak down tells you where the cylinder is the weakest
Bruce

[smokintr6]

At 135K you need head work

I disagree with that as a blanket statement. Top end overhauls are not inexpensive by any streatch. I would suggest having a leak down test performed, and then make an educated decsion from there. If the leak down looks good, and the car is not consuming a lot of oil, I would let it ride.

I guess it also depends on your definition of "a few intake an exhaust items". If that means swapping out the heat exchangers and adding a different air filter, then I still stand by my original statment. If you are bolting on a turbo, or making insane modifications, then in all reality you probably should go through the heads.

[smokintr6]

I just noticed you are from Columbus, Oh... I just moved to Kansas from Granville about three months ago. I miss that area!

If you are not doing the work yourself I know a great indy shop in the area that knows those cars inside and out. He could help you with any modifications, and would be able to give you an honest evaluation on the condition of your heads. AND his pricing blows the down town shops out of the water. PM me if you are interested in details.

[lindemans]

Valve guides will almost certainly have substantial wear at that mileage, allowing the valve stems to wobble in a way they should not be.

If you do the heads in time, you may prevent having to replace your valves before the stem,s get tapered...

[Steve@Rennsport]

Leakdown testing shows the condition of the valve sealing, however it doesn't tell you anything about guide wear.

JMHO, but at 135K, they almost always need guides and sometimes new exhaust valves (stem wear).

[cmcfaul]

rule of thumb, when the chains are stretched / tensioners are near or at the limit of holding tension.

Chris
73 911 e

[smokintr6]

[QUOTE]rule of thumb, when the chains are stretched / tensioners are near or at the limit of holding tension.
[QUOTE]

yep, and after 24 years his suspension bushings are surely trashed, and the paint is starting to age. He probably should just junk the whole thing and buy a new car

Oil consumption and valves that never stay "adjusted" can be a resonable assesment of the top end (including the guides). I guess I've never been one to throw the baby out with the bath water, especially when the bath water costs between $6-10k

If you've got the money, and you don't mind spending it on the car, and you want to make sure you get the last few %, by all means rebuild the top end. You are certainly at a mileage where many engines have started to show some wear. If you're only bolting a muffler and an airfilter on an otherwise healthy engine, save your money and keep enjoying the car.

Good luck with whatever you choose to do.

[DG624]

I have had some body work after some storm damage and was also restoring the interior. The car will look great so I was thinking the performance could be improved. Smokintr6 I agree that there is a bottomless pit for spending. I just didn't want to amke some changes with exhaust if I could save some money by doing needed cylinder head work also. I won't change it if it doesn't need replacing.

I have not noticed much oil consumption but just the usual blue smoke when it sits for a long time. A leak down test and compression test was recommended for basic engine wear analysis. I guess if there is good compression and power and no significant oli burning I should be good. Valve springs are probably worn and I should also check the chain tension.

[Walt Fricke]

DG624

Why do you think the valve springs are "worn?"

Sure, they have opened and closed many times. But they are made of pretty good stuff, and I bet seldom saw 6,000 rpm, and then not for any protracted time.

You can (or a shop can) remove an intake and an exhaust without taking the engine out of the car, and the springs can be checked on a spring checker to see if they are still good. In fact, I think about all that needs to be done is to check their length compared with a new spring. My understanding of springs is that they don't lose rate - coil springs may shorten, and torsion bars twist, but their rates don't really change.

If you decide to have a "valve job" done (which would include replacing the troublesome guides, though your oil consumption suggests you just might be lucky there?) with the seats and valve faces touched up, the springs of course have to be removed. So all can be checked. But I wouldn't tell the shop ahead of time to replace them.

Walt

[DG624]

I guess I was assuming that all springs lose tension after 100K but checking is the sure way to know. I also should remember the cost of these parts. Thanks for the advice.