Just got the head off my 850 turbo. Tech put me on a burnt valve when I got the car. You can see why I had no compression in cyl #4. As I was taking apart eng, thing looked to good, or new. I think the eng has been rebuilt recently. The head bolts looked new, timing components, hone marks on cylinders, no carbon build up, or ridges on top of cylinders. Should I keep tearing down the lower end? Car has over 300,000. on it.

 

Wow... that looks just like the head on my customer's car that I screwed up... the hole is even the same shape! Except in my case, it's a break from something getting sent through the valves and not a burn

Anyhow, if the cylinder walls look good, you SHOULD be okay with a valve job... but I would consider replacing rod bearings... as long as there's no play and no scoring on the journals, replacing them with a new set of new standard bearings just to play it safe should help it to stand up to its new- found vigor with a nice, tight head.

 

That is a burn hole it will be seen better once the valve is out of the head. You will be able to see the melted metal on the back side. Almost like if you were to heat it with a torch like you were going to cut it then let it cool. There will be little craters as well.

 

Oh and P.S. when it is all done do your self a favor and run premium gas to save the head from it doing it again.

 

Sooo...does that mean I should be running premium as well?

 

Yup, you should be, you can get away with regular, but should be premium. My car used to be my parents and they ran regular unleaded in it for I don't know how long, years, and I started using the middle grade, 89 or whatever it is, but it will be fine on regular, just probably not as good as it could be. Once my wagon project is done I will religiously run 93 in that.

 

After I do my tune up I'll run out the tank of reg and put in premium. I mean, there has to be a difference, otherwise they wouldn't sell it, lol.

 

All turbo cars should be running premium. Specially if it is modded.

As for the volvo, tough break.

 

Its up to you, did you do a compression test before pulling the head so you have an idea what the condition of the lower end is like?

 

Yep, compression was 160/160/160/0/150 pretty good for 300+ miles. I think I will pull the oil pan and have a look since it is on a eng stand.

 

The answer to the premium gas vs. regular gas question is this: These cars- even the turbos, CAN run regular. The car's engine management system can compensate for the difference by retarding ignition- that's what the knock sensors are for. However, particularly on the turbo cars, you will see a decrease in power and fuel economy. the difference is pretty noticeable. So while you're not likely to hurt anything by running regular, your car will run a lot better with premium.

 

Everyone also has to remember the regular gas of today is in no way what it was even 2 years ago. It has totally changed and not even done changing now.

We never used to see burnt valves on these cars till the gas prices shot way up there and everyone went to using regular gas because it was cheaper. Then we went to doing head jobs on car about 1 every 2 months without fail. We had even done a car 2 to 3 times because they did not take our advise and do all the valves in the head. They only did the valves for the cylinder that burnt.

 

Started running premium. Total difference. Now my car drives like it wants to go somewhere, lol. Thanks for the good tip guys!

 

Can you just add cans of octane booster to the tank?

 

just get premium