need info on 1991 "3800"

[Philippe Racicot]

Last weekend, after 235000 km of service my 91 Park Avenue's engine began to knock the day after my Buick dealer changed the oil... (curiously the samething happened to my 67 this summer, but on this one I changed the oil and I blew the engine...). Today I called in local junkyards and I found a couple of these. This is an an advantage of owning a 12 years old car because I had a lot more problems to find a rebuildable 430 for my Riviera! On of those guys asked me what was the eighth digit on my car's serial number because he said there were 3 different engines available in 1991 (one supercharged and two aspirated models) I told him my car's 8th digit was a L and he said he had the correct engine for my car... but it was too expansive. Other junkyards I called did not asked me about that. Some engines came from Oldsmobiles 98 and Toronados and others came from a 92 Bonneville and a 92 Regal. The least expansive came from a 91 Park Avenue just like mine but I have not checked it yet. I think that all 1991 to 1994 non supercharged 3800 would fit my car but I might be wrong. I would appreciate if someone could clarify this to me.

[NTX5467]

If it's a lower end bearing knock, why not just put a crank kit in it (reground crankshaft with matching bearings in it) and go on down the road? Might also add a new timing chain set at that time too.

Anytime you get a salvage yard engine, you're getting an "unknown" quantity, regardless of what the salvage yard people might tell you. In essence, you are basically getting a "core" that is rebuildable. Granted, there are many reputable salvage yard operators in this world, but they only know about the car the car has had since it came into their possesion. In other words, the "new" engine could have the same issues as the one you have in the near future--or you might get lucky.

Basically, if you're going to do an R&R, why not do it with your existing engine and freshen it up in the process. That way, you know what you've got AND only have to pull it out once.

As for the different versions, it might relate to whether the motor is a balance shaft motor or not. There might be something else I have forgotten about, though, which would be specific to your vehicle and hence make the motor more expensive.

I'd say to just rebuild what you have. Don't forget to figure some new mounts in the mix too if they are needed.

Just some thoughts,

NTX5467

[Philippe Racicot]

Thanks for the reply and happy new year! The reason why I preferred not to have my engine rebuilt is due to my past experience with escalading costs when you open an engine and decide to correct other problems. For example: my car's intake gasket leaks and it would be a good thing to replace it too. There is also a lifter noise that occurs when the engine is cold. As for the timing chain I had it changed about 3 months ago when I had to replace the magnet on the timing chain sprocket for the crank sensor. That's why my garagist wanted me to put new bearings on my engine. I might be wrong but I feel more confident to buy a relatively good used engine and keep mine for parts. Of course I'll check carefully the oil pressure and compression on an engine that is still in a car. I found one that costs 350 canadian $ and I have to check it next week. My main concern was to be sure that the replacement engine would fit in my car.

[Guest Albert]

Other times you can pick up a whole scrap car for a couple of hundred to with lower miles & a rusted body.. on the other hand i have picked up quite a few motors over the years from the scrap yards and had good luck with all, most yards check the compression before the motor is pulled and some will even tell you the current millage. I got one to replace a motor that went at 215,000k for the wifes car, the replacement motor i was told had 40k on it and it looked it, the car ended up with over 400,000km befor the car was totaled by her dad many years later.

[Guest]

Speaking of knocking engines- while my Buick 92 Park Avenue with a 3800 is still smooth and perfect running- my 95 Chrysler Concorde has developed a knock at idle. My dad said he thinks it is a rod bearing. Sad part is that it has only 91K, easy, well-maintained miles. It can only be heard at idle. I guess I will trade it in before the engine goes. I will NEVER buy another Chrysler product.

[NTX5467]

Instead of guessing about what's wrong with your Concorde engine, get it to a shop that is competent in Chrysler stuff as there are some noises those cars make that are easily mistaken for other things. End result is that a good bit of money is spent to needlessly replace a part that wasn't bad to start with when all it might have been was an exhaust seal that needed replacement. Might even be a bad engine mount too!

Chryslers still have several idiosyncracies that GM and Ford do not have. When a GM or Ford tech diagnoses them like what they are used to, with all due respect, they might come up with an incorrect diagnosis. As always, take the vehicle to someone that knows what they are looking at, regardless of what make or origin it is. Check out the FAQs at www.allpar.com too. There's also a Usenet newsgroup for Chrysler items. Something like www.rec/autos/makers/chrysler, if I recall correctly. There might be a link from the allpar.com site.

Just some thoughts . . .

NTX5467

[NTX5467]

Philippe, I know that there can be good engines in the salvage yards, or at least they were good when they came in there. Basically, if the issue is in the bottom end of the motor and providing there are no other issues with oil consumption via the rings or valve seals, there's no reason to bother those things.

In the middle '80s, it was somewhat common for a 3.8L Buick V-6 which had not received regular maintenance to develop a lower end knock as you describe. Basically, the oil galley in the block is rough cast to a particular size. Other GM carlines would use one long drill bit to machine them out to finished size, but Buick used two shorter drill bits, one from the front and one from the back. By design, they did not meet in the middle. If, perchance, the block's internal castings were not quite within the best relationship to each other, the drill bits might have a mismatch where they didn't meet. That area of the main oil galley is the area that feeds the center main bearing. In theory, it would receive sufficient oiling volume, but if gunk had built up in there due to poor maintenance, the oil supply was starved and guess where the knocking bearing always was. This typically happened at about 60-80,000 miles.

To replace the crankshaft and bearings, the engine must be removed and turned upside down on the engine stand. It's not necessary to take the heads off or disturb other areas (as pistons, rings) but the lower timing sprocket and related items would be affected. Back then, when people bought one of those cars (usually Regals for some reason) with a knock, they just put a crank kit in them and went on down the road. As you've already done the timing chain and cam interrupter, that's less to worry about.

If you've got an intake manifold leak, that needs to be fixed too. It could also be the reason for the knock if it's been there a while (from oil dilution with coolant) and undiscovered. Oil dilution will happen sooner or later if it's not fixed, either way.

As for compression checks, as it was pointed out many years ago by a dealership technician, all you're checking with a compression check is the top compression ring and how well it's sealing. An engine with good compression can still have compromised or worn oil rings which might not be doing a good job of scraping the oil from the cylinder walls, therefore letting oil get past the upper rings regardless of how well they were sealing. Hence, an engine with good compression can still have an oil consumption problem that is ring related.

I also know there are many good salvage yard operators, but I've heard stories of some that changed instrument clusters among like vehicles to sell the engines out of them. Naturally, the cluster had a low mileage for the year model. In more recent times, the clusters might be sold themselves as people don't want to send their defective clusters out for high dollar exhanges. End result, many times you're taking someone's word that can have little supporting evidence as a worst case scenario. Of course, if you can trace the vehicle back to the prior owner, those things can be verified, just as you might do if buying a used car.

In your area, it might be common to have a rusted car with reasonably low miles, but down here in the TX areas, we don't have that rust problem and we usually don't have engine problems with Buick V-6s either (other than some intake manifold leaks of late). The problems we saw when those cars were newer included the crank pulley/damper and the interrupter you mentioned. Everything else was pretty much bulletproof, which is why everyone got by with just doing crank kits on the earlier motors.

I fully understand cost overruns and such when starting to do a simple mechanical procedure. There are always things that are neat to do "while you're there", but if you don't have some guidelines in place, those things are sure to happen. Unchecked, a simple bearing job can end up as a full blown rebuild. Reality is, if the oil consumption is not an issue, the top side and rings will be ok so there's no need to get those replaced. Just because you might see some wear on the lower cylinder walls is no reason to rebore everything or get excited, especially if there are no existing piston knocks.

Anyway, just some additional thoughts. Of course, it's your car and your money.

Enjoy!

NTX5467

[Guest Shaffer]

Thanks NTX. That was me that posted about my Concorde. I thought I was logged on. I was thinking of selling the car anyway, to buy a newer car or truck, but liked it and did not want to sell it. I may take it to the repair shop we often take our cars to. Maybe they can hear what is wrong with it. Thanks again about the info on the site.

[Philippe Racicot]

Thanks for your reply NTX5467, I changed my mind and I'll do what you say. Before buying another engine I'll look at mine! It's oil consumption is reasonable and I know people that have done about 400 000 kms with these engines. These people had a much lighter right foot than me however! I just hope that repair cost will be reasonable so I could spend more on my 67's air conditionner and my 75 455 that has also been sick for a while. It was already in bad shape when I got that car over a year and 14000 miles ago and I was planning to rebuilt it before my 67 430's bottom end literraly exploded last summer and changed my priority order!