98 V70 GLT no comp on cyl 5-need some guidance

[northernlights]

When the shop gets the head, they will check all of the cylinders. There is NO reason to have other valves replaced, just the burnt one (or pair). If they rebuild the head, new stem seals, they will regrind all of the seats and valves to make sure they are in near new condition.

Have that cylinder injector tested and cleaned professionally.

One reason to replace exhaust valves - Stellite coating! Those are not supposed to be ground as the coating goes away.

There will be a loss of long term durability with uncoated valves, i.e. if someone grinds the exhaust valves. Does that matter on an old car? It depends how long you will own it!

[rspi]

One reason to replace exhaust valves - Stellite coating! Those are not supposed to be ground as the coating goes away.

Interesting... So this "coating" doesn't wear off over time? I was told that valves wear over time, as they are spinning in the head. One of the main reasons they burn, wear???

[northernlights]

I'm sure it wears, just very slowly. The coating significantly increases the durability at elevated temperatures. It's only on the exhaust valves, but notice they seem to be the only ones to burn...



There was a time not too long ago when it wasn't unusual for an engine to need the valves and seats ground after 30-50k miles. Technologies like Stellite coating helped to fix that problem.

[rspi]

Nice. Thanks for the info. I wonder if that coating is on the seating area???

Spoke to a guy a month ago that actually had an intake valve burn on his S70 T5. First intake valve burn I have seen on these cars.

[northernlights]

I don't know what the seats are made of. I know on the domestic V8s (Chevy's anyway) one could purchase aftermarket Stellite seats, but that was usually to eliminate the valve seat recession common to cast iron heads.

[shadetree_v70]

Well, i'm finally coming around to doing something about this. Ive parked the car for the summer but i will need it for winter so time to get fixin before bad weather sets in. I found a salvage 97 850R with 111k, and i think i could probably get the head and turbo for about $200 if i pull it myself.

Question 1: is that a direct swap to my GLT block or do i need to also grab the ECU, and/or other bits?

Question 2: if i pull my head and send it to be machined and replace the burnt valve, will the 15g turbo be a direct bolt on without causing problems like adding stress to a LPT head. My current turbo either needs replaced or rebuilt. The hinge for the wastegate is rattly loose, like the bushing disintegrated and smoke comes out right there.

Im also not averse to rebuilding the turbo with a kit, but i like the idea of component swapping for the sake of time management, with the idea of a rebuild in the future.

[erikv11]

1.) The T5 head is exactly the same as the one that came on your LPT.

2.) The 15g turbo is a direct swap. On standard boost (i.e. with your GLT ECU) there is no danger of damaging the engine. You will hardly notice any difference between the current 13g and the 15g if you keep the current ECU.

3.) It might be easier to just swap in the whole engine from the 855, I prefer that to cracking them open.

[erikv11]

BTW The 97 ECU will not work in your 98. Well it will work just great except it will fry the climate control module; the pinouts for A/C are different between 97 and 98.

[shadetree_v70]

I see your point about the whole engine swap, I just have no way to know what shape that one is in. For that matter, same with the head. Maybe the best route is simply to grab the 15g out of the junker and rework the head I already have to remove, since the turbo is a direct swap. More down time but less labor. Thanks a lot for your help!

[rspi]

The turbo may not be a direct swap. Some of them have the oil/coolant ports moved a little. Probably not a big deal.

If the car is wrecked, the motor is likely fine. I'm a head guy myself, it can be done without help and no special tools or lifts.

As for the motor swap, if you're not planning to build a 300 hp car, the lpt is fine. Some guys around here have actually tuned their lpt to be faster than the stock T5's.

If you only have a burnt valve you can pull the head, take out a valve or two and boy the valves instead of the entire head.