Olds engine question

[TC Chris]

Since you guys are saying kind things about Olds engines, I'll ask this. My 1965 Starfire's 425 engine has a rattle at cruising throttle. I have an idea that it's a worn timing chain and/or timing gears, letting the chain slap the cover. That might also explain diminished performance. I don't know if this one has nylon or other plastic timing gears. I bet one of you knows. The guy in the Starfire video was disappointed in the test car's acceleration. One comment said "it's an old engine, they get tired."

If I keep on working until I'm senile, which seems likely (working, that is, not senility), I may hire out a rebuild of the Olds engine. Or maybe the '38 Buick. Too many projects, not enough time.

Chris Campbell

[electra225]

It's probably got plastic teeth on the cam gear if the setup is factory original. If it was slapping bad enough to bang on the timing cover, I would think it would have already jumped time. A noise at cruise is almost impossible to troubleshoot via electronic communication. Loose flywheel, a dry center carrier bearing on the driveshaft, rough bearing in the water pump, alternator, or air conditioning compressor. Pre-ignition. Loose/worn/dry rocker arm or valve lifter, the list goes on and on and on. Best to have a live body do some quality troubleshooting, then report the results on here. Good luck.

If it makes you feel better, Olds engines are tough as nails. It is old, so there is that. If a little TLC is warranted, it doesn't owe you anything.

I have a huge amount of respect for the second generation of Oldsmobile engines. I wasn't as big a fan of the 394 and earlier engines due to the poor crankcase ventilation and the associated lifter noise. I've seen them sludged up so bad, when you remove the valve covers you couldn't see the rocker arms. Olds fixed that with the later 400, 425, 455, 330, 350 engines. They had good oil pumps, stout bottom ends and forged crankshafts. It's hard kill one. I don't believe I remember seeing an Olds engine that had spewed its guts. The timing chain usually goes out before the engine grenades.

[TC Chris]

What the heck, I'll speculate some more. Somehow spark knock did not occur to me. 10.5:1 compression plus lousy gas.... But then I'd expect it to be noisier under load than when just maintaining. It would be interesting to see what the compression is after all the heavy-foot driving I did.

No AC, so not that. No center carrier on driveshaft. Wouldn't a water pump be weeping? Never fiddled with lifter adjustment on that car (the Chevy, all the time).

And last, what dies when the timing train fails on this one? Do we have piston/valve collisions or does it just go far enough out of time to shut down?

Chris Campbell

[electra225]

It is not an "interference" engine in the strict sense. I'm guessing that if you were turning it about 5000 rpm when the chain failed, then all bets are off. Under normal operating conditions, the engine would just quit. Or fail to start like your Chevy did when its chain failed. When you are running breaker point ignition, particularly on a GM engine, the engine "wears out of time". The point gap closes gradually as the rubbing block wears. This increases the dwell time by making the clearance in the points closer. That tends to increase the timing, which, given the current "mouse milk" we have to burn, which tends to lead to pre-ignition, spark knock, pinging, whatever. And, yes, pinging can happen going down the road at freeway speeds. It is normally best heard under acceleration, but it happens at speed. I like the Pertronix "Ignitors" that replace and eliminate breaker points. This keeps dwell and timing constant and unchanging. Every firing sequence is like the last one, and like the next one. On a GM vehicle, I don't care if it's a four-cylinder Vega or a three-deuce big block, you want 36 degrees maximum timing at 1200 rpm. Not 1195, not 1205, 1200 rpm on the nose. And with the engine at operating temperature and with all accessories off. You need to make sure the timing mark is accurate. You can check that with a screwdriver in the plug hole and with a valve cover for #1 cylinder removed. Then mark the timing mark on the harmonic balancer accurately if it is proven not to be. You need to make sure the vacuum advance and the centrifugal advance mechanisms are working properly. Then using a throttle-setting tool, set the throttle via tachometer to exactly 1200 rpm and set the timing to 36 degrees maximum advance. You may need to use a timing light with an advance feature to do this. You would set such a device to 36 degrees then set the timing mark on the harmonic balancer to 0 (zero). The timing light will make the reading necessary for the 36 degrees of advance. There is no EGR valve on a car that old, so that won't be a concern. Determine there are no vacuum leaks and that the ignition system components are up to snuff before the timing is set. If you are not running the correct AC spark plugs, make sure the ones you are using are of the correct heat range. Too "hot" of a spark plug, meaning ones that the electrodes extend too far into the combustion chamber may cause pre-ignition as well. Too "cold" of a plug, too low an operating range, will run too cool, not extend far enough into the combustion chamber and may tend to cause hard starting, poorer fuel economy than normal, and may foul more easily. Also make sure the engine is not running with too lean of a fuel mixture. That raises combustion temps and may promote pre-ignition. Also make sure the engine is not overheating. If there is an idiot light for temperature indication, the engine may melt down about two seconds before you have to call the fire department and you not suspect a thing. Even if the engine is not overheating, per se, it may be running warmer than normal, say, 230 degrees. Not warm enough to cause damage, but warm enough to cause pre-ignition.

[Firedome]

Sorry Chris just saw this. As the Olds guy here I'd say this:
If you're using good gas (get no-ethanol Premium from a station that sells it, often near marinas, I would never use anything else in any vintage car) then the first thing to check is dwell and timing as per Greg. If they are off that by itself could cause spark knock. On an Olds V8 the usual is to set back timing from 7.5 BTDC to 5.0 BTDC the result being less pinging and slightly less power, and if it is a timing/gas quality problem the knock should go away. First year for the Rochester QuadraJet. There is also a chance it's idle speed mixture that's set too lean. The idle screws only control the mixture at idle, mixture at cruise is controlled by the jets. But mixture could be too lean at cruise if crappy ethanol fuel is being used. For Olds v8s it's recommended that the carb be re-jetted one or two steps larger when using ethanol gas. However the real answer is to use No ethanol Premium and make sure timing is spot-on, the little used per year is so trival expense shouldn't enter the picture when the engine's welfare is considered. Of course if the heads are majorly carboned up, maybe time for a valve job, or at least, an Italian tune up?

Going by memory the plug is a Delco R45-S but double check, however I greatly prefer NGK, I forget the equivalent #.

Shouldn't be the timing chain, If it jumped a tooth, it would run terribly, rattle would be the least of your problems!

Founder of OCA Blue & Gray Chapter, 1985...Oldsmobiles previously owned:
1936 Series F-36 sedan, 1947 78 Dynamic club coupe, 1950 98 sedan, 1956 98 Holiday sedan, 1956 Super 88 convert, 1957 Super 88 convert, 1958 Super 88 Sedan, 1965 Dynamic 88 convert, 1969 Toronado Custom (x 3), 1972 Cutlass S coupe, 1973 Delta 88 sedan, 1974 Delta 88 sedan, 1974 98 LS sedan, 1976 98 LS sedan, 1977 Delta 88 sedan., 1990 98 Regency.
Currently: 1969 Cutlass Holiday Sedan.

[Firedome]

BTW: up to '64 Olds V8 timing gears were iron, after '64 Olds V8 timing gears were aluminium with plastic coating on the gears to reduce noise. It's been known, rarely, with high age/miles, for that plastic to chip off and pieces to fall in the pan possibly clogging the oil intake. When I had my Rocket 350 rebuilt I used all metal gears.

To check timing chain wear you can remove the distributor cap, slowly rotate the engine in a clockwise direction until timing marks read zero and if you go past zero continue rotating the engine clockwise until they line up. When lined up slowly rotate the engine counterclockwise until you see the rotor move, then stop and read the timing marks again, the difference is the amount of slop in the chain. If it’s greater than about 5-10 degrees (don’t recall the actual spec) it's recommended to replace the chain/gear, very excessive slop could cause a jumped tooth, it happened on a Mopar 440 I had once. Stopped dead but no engine damage in that case.

[TC Chris]

All good info. The Olds hasn't been driven since about (guessing now) 1990, 1995. The move into current storage was via flatbed.

Chris Campbell