FYI, others in the Forum have stated the Volvo 960/S90 has an issue with burning valves. I lost a valve on #1 cylinder of our S90, no compression and the cylinder simply did not fire below about 2000 RPM. Several of the mechanics around Los Angeles thought is was probably due to "bad gas from Costco (not that we get our gas there)" and/or a failing injector, noting that they had seen this problem before. A reconditioned head is available from the dealers for about $2k (with substantial core charge), which is probably what the mechanics intend to use with quotes for the whole job around $3k.

I reconnected with an old machine shop I've used in the past and they will recondition the head for a lot less. In taking the head off, I've tried to pay particular attention to anything else that could have caused the problem or simply needed to be fixed. I would recommend anyone doing this to get the Technical Manual CD from FCPGroton, it has all the service and parts manuals for the 900 series cars. If you print all the associated pages for R&R it comes out to 22 pages (with a few assoicated illustrations from the parts manual), plus a further 6 pages on head reconditioning. Also, I have used nearly a box of Ziploc bags to label where all the parts came from.

I have found what I think is the cause for my problem and it could be the cause of some others as well. I'll attach an image of the intake gasket, which to my surprise has a very uneven distribution of mounting bolts. In particular, the #1 and #6 cylinders have a single bolt on the opposite ends that are a significant distance for the center of the manifold that has a more even distribution of bolts. I think this issue with the end cylinders was compounded in my case by a gasket that collapsed a bit over the years and possibly a lack of attention during the original build process. I would note that I'm an original owner and I know that this part of the car has never been previously apart. Without removing the injector trim cover (it does just pop off) and some serious inspection, you can't even see the intake manifold bolts. In my case, ALL but one of the manifold mounting bolts were just barely tight, the exception was the #1 bolt which to my surprise I could simply remove with my fingers.

I now consider that this condition of the bolts and some indication on the gasket itself shows an air leak into the #1 cyclinder. This caused a lean operating condition and probably resulted in the burned valve, with part throttle (low RPM) operation at higher vacuum being the most lean. I had wondered a bit about the postulated causes by the local mechanics, since this is my wife's car and it would be unusual if she had it above 2500 RPM.

I would recommend that anyone into the area around the injectors to check the torque on the manifold bolts. I have done this kind of thing on my other cars, but it was simply "out of sight, out of mind" on my wife's car which was normally maintained by the dealer and local specialist shops.

 

Sorry to read about your burnt valve. I have read a lot of information about valves burning because it seems that these Volvo white blocks experience this issue more than other cars.

I believe all of the burnt valves are exhaust valves. I've seen them burnt on cars with miles as low as 61,000. I initially thought the primary cause was people running normal 87 octane fuel, 91+ is recommended in the 960's. Now I believe the primary cause is leaky valve stem seals that are worn due to the use of oil filters that do NOT measure up to the Mann/OEM standards.

So, I have 2 questions for you...
1. Was Volvo or Mann oil filters used on the car since new?
2. What octane fuel was used in the car most if the time?

 

Not sure that I'll help your theory, we normally run premium gas (considering prices in LA, a slight reduction in mileage would eat up most of the 3-4% cost advantage for regular). I state normally because my wife may have used lower grade on occasion, but I told her to never even consider using anything below the mid-grade level. I have generally used only Volvo OEM oil filters, getting them from a dealer on the internet, and I've always changed the oil with lately a synthetic blend every 6 months / 5000 miles figuring that is cheap insurance. Since the car is now at 135k miles, the new oil picks up the darker color of contamination fairly quickly, but I have not found any areas of the "sludge" that you used to see at engine teardowns in the past.

While on OEM parts and stuff, I've always used Volvo sourced brake parts from the same dealer as that is a key safety area. Onw advantage when replacing rotors is that Volvo OEM rotors were marked for alignment a particular area on the hubs to minimize runout, this worked out very well for me as the replacement rotors were always within runout spec without having to be ground (I don't have the machine to do that). I also used the Volvo OEM pads, more for convenience in ordering them at the same time since a large enough order from the dealer shipped free. At my last order the dealer indicated the part numbers had changed, but that had happened infrequently in the past and I didn't think about it very much. However, I was not happy to find that the new version rotors in Volvo OEM boxes were now from China vs Italy / Brembo and that the Volvo OEM brake pads were from India vs Denmark. Afetrmarket is looking much better now!

 

A bit of an update. While I still do not like the Volvo intake gasket / mounting interface design, I had all the injectors tested and they did find a bad one. The injectors were sent out for this by the machine shop doing the head work and unfortunately the cyclinder numbers that I put on the injectors was wiped off during the testings / rework. However, it is probably likely that a bad injector was the primary cause of my burned valve, see photo.

I'm still working on a few things before putting everything back together, hoping I don't have a head bolt pull out. When removing the head, one of the bolts did not come quickly free. I worked it back an forth a lot, and tried to flood the thread area with WD-40, let it cool between every partial turn, etc. but found this one bolt had some corrosion (or something like that) which picked up some of the aluminum in the threads. I did test a good bolt to the 40 ft-lb pre-stretch torque and that was OK. So I really hope I'm not into heli-arc, etc. in order to get the engine back together.

I've worked on a lot of DOHC designs and the Volvo 6 engine is much more difficult to work on than most. I've been very careful to keep tract of the crank and cam positions so it can go back together the same way, but there are essentially none of the common timing marks and you need several Volvo special tools if you mess this up.

 

The machine shop that fixed the broken valve recommended that they perform a pressure check of the head collant system first, which passed. They told me that the 2.9 6 cyclinder head has a poor record for cracks, which I can believe. I feel that the air injection passages being cast into the head make this issue worse, and it bit me in the end. When I put the repaired head on the car (following the factory installation torque instructions exactly), the cylinder with the bad valve was fixed (engine runs fine to a point), but there is now a small crack that leaks coolant into an exhaust port. Nothing visible when the engine is cold, but a slight white cloud of steam follows the car after the engine gets warm and the coolant system does not develop any pressure. The compression is fine and there is no indication of coolant / oil mixing or combustion gas in the coolant, so the head gasket is actually fine.

Due to other issues (some simply cosmetic) with a fairly high mileage car, I did not feel like springing for the Volvo sourced rebuilt head. However, we did finally find another S90 that was built in October (ours was March) 1997 that had only 54k miles. It had some fairly apparent minor mechanical / cosmetic issues that I could repair by swapping parts off our old car. So my wife is now happy again.

 

Man, sorry to read about the head install issue. As for the burnt valve, how long did you own the car before the valve finally chipped? Is it possible that it may have had a small crack and finally enlarged and cracked? Probably not. Those exhaust valves get so hot that they likely fail within minutes of developing any crack.

This is the first that I have read about a white block I6 having issues after a head rebuild. I have not had to do one yet but just the size of them bother me.

Glad to read that you have another on the road and running well. Maybe running some Lucas fuel injector cleaner through the tank every other month or something can help with keeping the valve path clean and trouble free. I run the cleaner through my motor every 90 days or 2,500 miles. Over the past 18 months I have averaged 2,200 miles per month so I do it every 5 to 6 weeks.

 

I'm a little pissed because the site crashed after I created a long reply, but here goes again. However, you will miss my somewhat long winded discussion of the issues I have with the 2.9 liter S90 engine design that included overly complicated head design, poor practice when coarse bolts are simply threaded into aluminium, etc.

We purchased the 1997 S90 new, basically it was my wife's car and she just loved it (still does) so it had a fairly easy life. The valve failed at 129k miles, while cruising on the freeway at about 70 MPH. Initial indication was a vibration, which was reduced when not on the gas, but the car would run at freeway speed. Our destination off-ramp was only a couple of miles away, so I continued until we arrived for an afternoon concert. The S90 ran very rough on surface streets, unless above about 20 MPH / 1500 RPM where it was just somewhat bad. At this point the check engine light was on and I thought it was an ignition problem.

After a careful drive home on surface streets, I found the OBD indicated a couple of misfires. One was simply a bad coil connection, so now I had 5 cylinders instead of 4 and the car ran OK above about 2000 RPM. After swapping coils and the ignition control modules, the problem stayed with the #1 cylinder. I then found my compression tester had died and after getting a new one found that the problem was zero compression at cranking speed (no plugs installed), with the other cylinders all at near 200 psi. since there were no other indications of a failed head gasket, my thoughts turned to a valve failure.

Side note, the rubber in the plug coil connectors on our car was all rotten and the vibration at the valve failure had caused another cylinder to drop out due to a loose coil connection. I then cut all the coil connectors apart and plugged the contacts directly into the coils, watch polarity and tape them in place if you do this. I have now found that the FCP sourced side indicator light wiring kits probably can also be used to fix the plug coil connectors as well. See my other posts on the rubber vac fittings and OBD monitors, the SMOG here in LA is a real problem for rubber degradation on the Volvos.

Since our car had some other issues (clearcoat starting to flake off, torque converter probably making some noise, etc.) the quotes for repair from the Volvo mechanics in our area were more that the car was worth. After looking at a lot of other cars, I decided to attempt the repair myself, at about $900 out of pocket in the end. I have prior (but not recent, due to time constraints) experience with engine overhauls on racing cars and aircraft and I do have the Volvo manuals. I think I was a bit unlucky in that the head cracked at installation, which I think is somewhat due to the overly complex head design (24 valves, air injection passages in the head as well, etc.). I also have older Alfa Romeos and Maseratis, they are MUCH easier to work on than the Volvo and I know exactly how much Maserati spent making their cars maintenance friendly, zero!!

In hindsight, I now see that there was a slight increase in HC readings at our SMOG tests that started in 2007. The computer probably somewhat compensated at the SMOG / cat level for a failing injector, but that likely caused the eventual valve failue.

 

So you think it was likely running lean?

You can thank Porsche for the motor design. I use to run the dog crap out of my last S90. I mean long runs like I was the last person on earth. Do you think it was something injector cleaner would have helped?

 

My guess is that the cylinder with the burned valve was running lean, but not enough that we could tell in normal LA local driving (about half the time stopped in traffic). I normally used some injection cleaner every two years, before the car was due for SMOG testing and tried to do a 30 - 50 mile freeway run at the same time. Also, in 2007 we stopped using the car for long trips and it really became the car for just local trips and that might have not been particulary good for the injectors.

 

Hi Bob-

Sorry to hear about your troubles, but glad you were able to get going again. As to your post on the intake gasket- it may not have caused your issue with the burnt valve, but it is definitely a known issue on these cars that the gasket fails and causes vacuum leaks. I had this problem on mine, and as you noted, the bolts were definitely not tight when I was removing them. And, it was cylinder #1 where the problem was found.

Thanks-
Brady

 

Thanks Brady,

The really unfortunate thing is that you can't even see the front intake manifold bolt unless the upper radiator hose is off and most of the upper bolts are hidden by the aluminum trim cover over the injectors. Until I got into the repair above, I did not reealize that the trim cover was a separate piece that could easily be removed from the fuel rail.

The 98 we purchased with 54k miles is now running fine, but I'm still catching up on some of the maintenance that was never done (fuel filter, etc.).

 

Well, I visited a few shops that really have me believing that burnt valves are the result of poor fuel/air mix so a leaking intake or bad injector will likely cause one to burn. Running rich or lean they claim causes it.