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In the past, I've opened up 100 K miles Oldsmobiles (425/455) engines and even though the chain was a little sloppy, the neoprene gear was in decent shape. All these cars were "older" owned. I'm under the opinion, that when they wear to a certain point, they go bad fast. This is a 1975 Olds 350. Engine has 97 K miles on it. It ran smooth. It's been sitting for around 4 years. I put it on the engine stand. Fresh oil and filter, pulled the HEI out, primed the engine, reinstall the HEI. I decided to do a compression test plus spinning it over is a plus in my way of thinking. Each cylinder was 125 psi give or take a few. It fired easily, idled smooth. I have receipts, former owner had a water pump, fuel pump, rebuilt Quadrajet &tune up. Hmmm, no timing chain. I pulled the fuel pump, socket on balancer, turned a bit, "finger'd the hole." As usual, a little sloppy. (:•》Anyway I started unbolting, opened the front cover and I was pleasantly surprised, the neoprene on the cam gear was in good shape. I always say, those Oldsmobile Engineers were pretty smart. Most these engines were designed for reliable, quite running, operating. I glad I don't have to drop the oil pan, so far. That's enough MAW for this engine. Plans are for installing this engine in my Grey 1967 Oldsmobile 98 then sell it. I have 3:08 rearend in it so it shouldn't be too bad. This engine moved a 1975 Royale convertible for 4 decades.
I have found similar, mid 70's Olds V8 were super reliable. Yeah a neoprene rear main seal is a good idea if going that far along with new gaskets. The Felpro Conversion set is $12, just add a Neoprene rear main the same price, so a resealed motor for $25.
It wasn't made out of neoprene it was nylon. Oldsmobile/GM were not the only manufacturer to use them. I would not glorify that part, they were not reliable and failed leaving the bits of plastic in the pan to be sucked up into the oil pickup. The timing set was the cause of many engine failures. You are in the minority to have found one in good shape at 100k miles.
Eric is correct, it's nylon. Neoprene is what wetsuits are made out of.
This gear looks similar to the one I pulled from a 100,000+ mile 307. I was completely surprised that there were any teeth left at all, yet it was still serviceable. Apparently Olds must have changed the nylon formulation from the 60s to the mid-70s and later.
My 79 H/O had on 55k on it and most all of the teeth were in the oil pump pickup screen. The aluminum teeth underneath were starting to curve over from the chain pulling on them. I was amazed that it still ran when I disassembled it.
I pulled one out of a 100,000 mile W-30 with 3.91 gears and it was in great condition. I also pulled them out of other 100,000 mile cars and were trashed. My dad bought a 77 Cutlass new and that car went 280,000 miles on the original timing set. That was the first time to open the engine at 280K miles. A new timing set and it went to a little over 300K when we quit driving it. At 300K it still did not use a drop of oil.
I got about 450,000 km out of one, I bet it looked like Bill K's, never pulled it down. It still only used 1/2 Liter every 4000 km but I had a spare 307. It was a 307 in a 81 Delta 88, one of the best cars our family owned, only paid $500. I had all the bills from when it was purchased new in 82, wish I would have kept them, very well taken care of.
I had an 83 Cutlass with a Buick V6. One day, it would fire right up, then die as soon as you put the car in drive. The nylon gear ended up being the problem. 88,000 miles and 13 years old. The teeth weren't broken, just worn out.
Last edited by 1967Supreeeme; December 23rd, 2019 at 11:40 AM.
I was amazed that hers ran as long as it did And actually it was running pretty good. She came home from work one day and had to stop at the end of our street to let another car go by. When she hit the gas to turn down our street it gave up In all reality other than the timing set the engine was in remarkable condition inside. It did barely bend a couple of exhaust valves.
How many degrees of crank is it taking to rotate the cam gear, If I turn my crankshaft with a wrench I'm getting 7 degrees before the distributor moves. I suspect I skipped a tooth or it's so worn so bad I can't get the timing correct, though I still have other things to check.
My 88 Caprice had steel, I could peak through the hole when I had the manifold off, so they did change at some point during the 80's. I had a 72 Eldorado still running nice and smooth at 120,000 but had another Caddy go at around the same, it sucked to replace, similar to an olds motor. the pan needs to be dropped to do it right.
I had read that racers back in the day actually used stock nylon gears because they were never worried about piling up enough miles for it to matter, engines were always being torn down.
The only reason I started this thread was to show that in some instances these "nylon/polymer" can hold up in the right conditions. At least 3 times I've seen 100K mile engines with them in good shape. All were owned by "older" people. Earliest was a 1967 425. I've seen a few engines with the oil pump screens clog full of chunks of "nylon/polymer" but the engines weren't damaged. Here is an example, in the link I'm including, of a clogged screen. The crankshaft on the 400 E was std/std and in decent shape except there was one groove and a tiny chunk of metal embedded in the bearing. The bearing did it's job, imo. One piston had a cracked ring gland hence the metal.
This is why I suggest if the "nylon/polymer" is gone to pull the pan, check the screen. jmo. https://classicoldsmobile.com/forums...ebuild-139796/
Back in the '80s I had a beautiful triple black '75 Regency(1 of my all time favorite cars) The original engine made it to 286k but it started to use more oil than I was willing to tolerate & it would foul out the #3 plug(kind of hard to do with HEI). I had a real nice '72 455 with 60k on it, waiting to go in the car. After I got the old motor out I opened it up just to see what I had after all those miles. The rings had lost their tension in the #3 hole & the cylinder wall looked like it chrome plated it was so shiny!! The other 7, except for a little top ridge looked pretty good. The timing set looked amazingly good, the chain was a little sloppy but all the nylon teeth were intact. Even the bearings looked good. I probably could have honed the bad cylinder, put rings on the 1 piston & it might have run for many more miles!!!
It wasn't made out of neoprene it was nylon. Oldsmobile/GM were not the only manufacturer to use them. I would not glorify that part, they were not reliable and failed leaving the bits of plastic in the pan to be sucked up into the oil pickup. The timing set was the cause of many engine failures. You are in the minority to have found one in good shape at 100k miles.
Yeah I had a timing set go on me while driving on a parkway. 1967 330 just over 100,000 miles. The teeth were nubs, how it drove that far is beyond me. The timing set is the only real knock on cars like ours, and the reason people would say the cars are good for 100,000 miles before major issues. I was essentially the second owner since about 42,000 miles, I was young and did get on the car. Ran great just before as it did right after the timing set replacement. So very hard to know whats what.
Originally Posted by Kennybill
The only reason I started this thread was to show that in some instances these "nylon/polymer" can hold up in the right conditions. At least 3 times I've seen 100K mile engines with them in good shape. All were owned by "older" people.
I believe it, I purchased a 1972 98 455 many moons ago, older female owned, 100,000 miler. The car ran great ! Had intended to swap the engine out. My mechanic at the time convinced me that it was best to get it rebuilt now rather than later. I assured him the engine was ready to go as is... In the end he won out, I mean after all it did make sense.
One day during the process he tells me I was right, the engine was clean and in great shape once pulled apart. Don't remember details on the timing set but I'm guessing it was part of the great shape. The car had lived a nice easy life likely under 2000 RPM for the vast majority of it.
Still I would agree with oldcutlass, so much so that I recently had my 69s timing set replaced even though I thought is was ok to go. Once a fellow member planted that seed i couldn't shake it. In the end the set had already been replaced but i couldn't confirm it without having it opened up. It definitely had some mileage on it and some stretch, but i could of gotten away with it for a while. Regardless now I have absolute peace of mind.
How many degrees of crank is it taking to rotate the cam gear, If I turn my crankshaft with a wrench I'm getting 7 degrees before the distributor moves. I suspect I skipped a tooth or it's so worn so bad I can't get the timing correct, though I still have other things to check.
.
In the old days , back when these things were in vogue .
The shop where I worked had the following standard for timing chain " slack ".
four degrees or less was OK. At six degrees the engines would run but poorly . Eight degrees or more was "out to lunch " .
Replace it .
Last edited by Charlie Jones; December 24th, 2019 at 07:20 PM.
December 22nd, 2019, 10:33 AM
And actually it was running pretty good. She came home from work one day and had to stop at the end of our street to let another car go by. When she hit the gas to turn down our street it gave up 
In all reality other than the timing set the engine was in remarkable condition inside. It did barely bend a couple of exhaust valves.
