Hey everyone. I just bought my second volvo. My first was a 1983 244 Diesel in college with 280k miles. Great car but back to the point. My 1988 740 (non-turbo gas) has an engine knock. Not a ping during load, a consistent knock. It's pretty loud and seems to occur at a rate of half the rpm. I'm thinking it's a valve but here's where I need help. If it was a piston wouldn't it knock once per revolution or would it knock only on combustion which would be once per 2 revolutions. I'm really hoping it's a valve with a clearance issue. I live in Boston with on street parking so I bought it for basic transportation (and I love old volvos). It has 163k miles on it and it was well maintained (oil changes, flame trap always kept clean, no oil leaks). The idle is a little rough but it runs pretty well. The last owner bought it new but it became the kids car for the last 10 years. 3 boys drove the car through high school. Could have been over-revved etc. I'm also looking for feedback on what the typical problems are in terms of piston slap, valve clearances, etc. Thanks!!!

 

is this a twin cam or single cam?

wait for the experts to get on...

 

Regardless, a teardown will be needed to find the problem. You could use a mechanic's stethoscope to pinpoint whether the noise is from the top or bottom end.

 

It's the single cam engine. It doesn't seem to burn a drop of oil and there are no leaks. Amazing for the year and mileage...

That's a good idea using a stethescope. I'll give it a try.
I was hoping that a valve clearance adjustment (shims) would solve the issue and prevent more damage but it sounds like it's a bigger problem. I paid $800 for it so I'm just going to drive it easy until it blows up and then find a good used motor (if any are still out there).
Thanks for the help.

 

Cheaper than a mechanics stethescope is a wooden dowl. Though going by what your saying it sounds like a rod is coming apart in the motor. you can put a strong magnet on your oil filter and run the car for a week then drain your oil, look for metal shavings take your oil filter off and cut it open and look for metal shavings. Chances are you need a new bottom end. I would get one before the piston decides to let loose and possibly also destroy the head.

 

It's rare that that motor would have that problem with such low mileage unless it was really neglected in oil maintenance. Are sure it had good oil changes? It does sound like a "rod knock"--the death of a motor. It is not worth rebuilding--I'd get a used motor from a junkyard--plenty of them around. You should be done for around $500.

 

If it's at half engine rpm it may be piston pin, rod knock or some other similar issues.
To determine if it is a bottom end issue, remove one spark plug lead at a time and listen for a change in the noise. Removing a plug lead eliminates the power stroke and if the issue is bottom end, unloads or loads up the components differently.

Regards, Andrew.

 

I didn't even think about taking off a plug wire. Great advice. I'll try it tonight after work. I ran chevron fuel injector cleaner through the system last week and the engine idles perfectly now. The knock is obviously not going away but it hasn't affected how it runs. Hopefully I can get through the winter with it.

Thanks for everyone's help.

 

Piston slap is not uncommon in these engines, so if it were me, I'd not get too upset right at the moment. They'll run forever and be noisy doing it the Volvo fours.

Regards, Andrew.