Truck doesn't start. I tried all the usual things and gave up on my own. A local highly recommended mechanic told me that based on my description, I need a new timing chain (this is an '84 with less than 80K miles!) but he said in his experience, these old 302's have very little valve clearance and it probably isn't worth the $500 to replace the timing chain since it is almost certain that I have bent valves as well and we won't know until he replaces the chain. He said if the cover bollts are seized, which is likely, it could run over $1000. I told him the bolts may be ok since the engine is always oily. It has always blown oil (not alot, maybe a quart a month) out everywhere. He said I have severe blow-by indicating bad pistons or rings. He recommended I junk my truck! Does any one agree with this theory? I'm going to tow it to him first and have him confirm his sight-unseen diagnosis. I would have thought with only 79K, I could get another 100K out of this truck. -Norm

 

Waay too easy to check for bent valves before chain replacement. It doesn't matter how oily the outside of the engine is, the bolts seize in the aluminum timing cover. With no more miles than that I sincerely doubt that much of a problem with the timing chain.

 

your description doesn't all add up really. I'm not sure how you get from a truck don't start to timing chain is bad and having bent valves.

I would start with a compression check of all 8 cyclinders if bent valves are suspected.

If the problem is that it just don't start...then start with the basics...check for fuel and spark (with correct timing). If you have decent compression with fuel and spark at the right time then that's a good start.

 

Also....$500 to replace a timing chain?? There is a fair amount of work to do but none if it is that complicated.

If you KNOW it needs one, buy one and a torque wrench and replace it. Most parts stores will let you borrow/rent the torque wrench. It's not that difficult. Make sure it's on TDC on the compression stroke and get a good manual. But make sure you need it first.

 

I have seen very few bent valves in any 70-80's model USA V8 engines, that were related to a timing chain. The comp ratio is rather low, and the stock cam is rather short on lift, for interference to occur.

The engine may only have ~80K miles on it, but it's still nearly 30 years old. The stock cam gear had plastic/fiber teeth, and they can/do rot away over time, driven or not.

 

Very true....I had a leak on the timing cover on my 460 with 140k miles. When I pulled it off the chain was very loose and had 4 of those plastic teeth broke off. But it never skipped a link and certainly didn't have bent valves. I would think that if you had interference issues you would put a hole in the top of the piston before you bent a valve.

 

If the engine is stock (not a high lift cam and high compression pistons) then I don't think it will have piston/valve interference.

 

I've seen a 60s version 289 with enough slop in the chain that it wore a hole in the side of the T/C cover - no bent valves tho'.

I've also seen an early 70s small block swallow a valve. Completely merged with the piston. They drove it in and it started every time. Noisy as hell but it started.

 

Thanks everyone. For clarity, Kevin, I did the basic checks of fuel, spark and compression. It drove one day like it was in 3rd gear accellerating real slow but it reached 70 mph and seemed fine at that speed until I parked it and it never started again. Compression was eratic 80 lbs one time, 40 lbs next time; all cylinders were like that. Also had an incident a few days earlier parked in heavy rain some water got on the air cleaner and it blew white smoke (steam) out the tail pipe for a few seconds but it ran okay for a couple days. I thought maybe I had a blown head gasket. Since I really don't know what the problem is, I decided to take to an experienced mechanic. This guy was the president of the local Pontiac club and rebuilds carburated engines. I'm told he really knows his stuff. He's sure I've skipped a couple teeth on the timing gear from what I told him. He said it was a common problem on early 302's even with low mileage, maybe because of the nylon gears? I'm towing it in today. I'll post the final analysis. -Norm

 

Eratic compression readings would be a good indicator of the chain/gears needing replaced.
I bet while cranking it over, it sounds like it's almost going to start every once in a while, but never does, and the cranking sound changes while it's turning over.......

 

YEP! -Norm

 

Okay, Good news is my truck is running great now. Yes, those plastic timing gears were all torn up. No bent valves. What was Ford thinking when they put plastic in there? Makes me wanna buy a Chevy (no, not really).
Norm

 

Great....glad it was confined to just that then

 

Chevy also used nylon/nylon coated timing gears.

 

The nylon (coated) gears are quieter.