How many miles for an orignal motor?

[redhorseshoe]

I have a '73 with about 110,000 on it and wondering how many miles I can reasonably expect to get out of the original 302 before it needs overhauled/replaced. I know there's too many variables to mention that affect this but just hoping for a rough estimate. Mine's in good shape, starts, runs, and drives good.

 

[blubuckaroo]

There's really no reason your factory motor couldn't be healthy past 200K.

It depends on regular maintenance and how many little maintenance repairs you're willing to keep up with.

Your factory engine came with a carb that needs more frequent oil changes regardless of the mileage intervals.

Carbed engines also need more frequent tune-ups.

Scheduled coolant replacement is important too to avoid corrosion.

Maintenance items like water pumps, gaskets, main seals, and valve guide seals will be necessary along the way.
None of these things were designed to last the life of the motor, and they can all be done with the engine in the car.

 

[redhorseshoe]

That's really what I was hoping for. I've been replacing small things just to keep it in decent shape. Rebuilt carb here, new coil there, that kind of stuff. Someday I'd like to put a new motor in it but am really enjoying things the way they are for now.

 

[.94 OR]

I'm in the same boat. I think the engine had a rough life before I bought it. Since I bought it when I was 19 I know I wasn't easy on it for the couple years I drove it before it got wrecked. I'd be surprised if I drove it 3000 miles in the last 25 years. Glad it is no longer my daily driver.

 

[BajaBronco]

If it hasn't been done, I'd recommend a new timing chain. Originally a 1973 would have had a plastic composite gear set and they do go bad. Let me see if I can find pics of a Baja I had with 120k on it, ran great compression and carb side of things, did water pump as it was leaking and decided to pull cover off. Glad I did.

 

[Master Chief]

If it hasn't been done, I'd recommend a new timing chain. Originally a 1973 would have had a plastic composite gear set and they do go bad. Let me see if I can find pics of a Baja I had with 120k on it, ran great compression and carb side of things, did water pump as it was leaking and decided to pull cover off. Glad I did.

At the very least, I recommend this too. This morning I dismantled a 1971 302 pulled from an F100 with 135,000 miles on the odometer. The timing chain was loose enough to skip across the sprockets because of the numerous teeth that were chipped off the composite gear. The cylinders look great but one paper thin cam bearing came out with the cam so I imagine it may have been close to failure. The main and rod bearings have normal wear, no surprises there.

 

[Rustytruck]

The 40 year old steel clad head gaskets should be replaced. Bronco water pumps don't like to sit around and last about 10 years or so. Use to get 10 years on mechanical fuel pumps now days seems to be lucky to get 5 years unless running pure gasoline instead of blends. Adjust the points every 10,000 miles and replace the plugs every 30,000 miles

 

[sykanr0ng]

Carb engines that run rich have the excess gas wash the oil from the cylinder walls quicker at shutdown.

 

[ugly74]

When I bought my 74, the man I bought it from was certain it had over 300k with the original reciprocating assembly. It had had head gaskets, timing chain, water pump, etc done to it, but still ran good. Smoked at start up an was leaky, but....

When I rebuilt it about a year later, the bearings were dated '73.

Take care of it and they'll last a long time.

 

[DirtDonk]

Yep, what they said.
The only thing I had done to my '71 302 was a valve job, new lifters only and timing chain at about 95k. It had been rode hard and put away wet for it's first 50 to 60 thousand miles, and it showed. But once a little chemical magic, daily driving and a couple of parts had been throw at it, that engine gave great service until I sold it with 175k on it. Still ran great and only used a quart of oil between changes.
For years that was on quart every 5000 miles (my chosen change interval) to about one quart every 2500 miles at the end. By then though, I was actually changing the oil every 3000 miles too. Which is, I believe, the factory recommendation for ours under similar circumstances.

Good luck with yours. Glad it's still running good at this point.
Keep up the good work!

Paul

 

[ep67bro]

At least 100K. My 73 had at least 120,000 on it when I took it apart last year. had original bearings, head gaskets and other internals. She was worn out did not have good compression but ran, I did a basic over haul and its still alive now. How it was maintained is key. I say if she runs, keep her going!

 

[blubuckaroo]

I just looked at my maintenance records, and our first rebuild was at 199,162 miles.

It had a little top cylinder ridge. The motor still ran ok, and had fair oil pressure, but had a burned valve. Evidently, even though it was a '77, and made for unleaded fuel, the early seats weren't hardened as necessary for modern fuel.

The only previous work was a timing chain set at 76K and a couple water pumps & fuel pumps along the way.

I just figured, rebuilding just the heads at that mileage was throwing good money after bad. I pulled the motor & tranny, had both rebuilt, and reinstalled them in '02.

I did the next and previous rebuild myself.

I'm a bit of a "maintenance nerd" and I do believe that's why the first motor lasted as long as it did.

The last build wasn't even necessary. I found its problem was just a bad intake gasket vacuum leak in the valley, but I had already talked myself into different pistons and heads.%)