72 304 Rebuilding Questions.

I am starting the rebuild of my '72 304 rebuild. Started with bad starter and ring gear. Long story short I have decided that while it is out for that repair I am going to do the rebuild. First do any of you have recommendations on the master kit? and source for crank kit or just have the one i have reground? Next I have discovered that the PO replaced the original alternator with a GM one wire I believe and backyard engineered the mounting. Is there a source for brackets and does anyone know if there was a preferred alternator that was used for that swap? Motor will be out tonight so I hope to get it to the shop by the end of the week.

 

I've never bought a kit, but instead bought the parts I needed. Pistons will be your biggest expense if you go for the full rebuild. You won't know the size until your shop measures your block. I have bought crank kits from the shop that did the work and they came with the proper sized bearings. Whatever core you take to them, they will give you one size under for a replacement crank.

I enjoy rebuilding engines, but I think today a long block sometimes called a "crate engine" (not really a crate engine to my understanding - that's a new motor) will likely be comparable in cost once you add up the parts and machining. Worth looking into.

I'm not sure about a '72 wrt the alternator... I would search the AMC Forums and maybe this has come up. The original alternator would be a Motorola, and they have a poor reputation. The favorite for replacement is a GM Delco 10SI, but IIRC they are too big for the factory mounting. Lots on the net about the 10SI. Supposedly there are Denso alternators that are quite a lot smaller and work well for swaps.

For the brackets, a junkyard or part-out will be your only source. i don't have a book that shows the '72 alternator mounting, but I think it will be the same for all the AMC V8s '71-74. Here's the '74 drawing - you can compare to what you have.

 

Thanks Tim I have just the bell housing bolts to go tonight I have been looking at the long blocks, I want to look and see whats inside this motor and do some checking locally. You are never sure what the new one was thru before the engine rebuilders got there hands on it

 

Why do you think you need a crank kit? Disassemble your engine (carefully) and see what it needs. Do you know you have to keep each lifter in the exact order they were installed, if the can and lifters are good enough to reuse? Don't assume you need to buy a bunch of parts, unless the engine has obvious problems. I have pulled a lot of engines down where all that was needed was a light cylinder deglaze, rings, lap the valves, and fresh gaskets. If the crank needs grinding. a good machine shop should have this capability.
-Donny

 

Following up a bit after Donny's comments ... The horse may be out of the barn in this case, but I would first measure the compression wet and dry, and note the hot running and hot idle oil pressure. A rebuilt or refreshed engine won't make any more power than a seasoned engine with good compression. And a seasoned engine is a reliable engine.

Good practice would be to start a notebook and keep track of all this relevant data. A compression tester is cheap, and tracking the compression will give you a much better idea of your engine's condition. Measure, measure, measure.

You can also keep track of the oil pressure. The factory gauges aren't particularly accurate and have a lengthy settling time, but you can detect a trend, if present. (If I saw a sudden change and were following the factory gauge, I would suspect the sender/gauge first). These engines (Gen 3 AMC V8s) often develop very low hot idle oil pressure (ie less than 10psi) at high mileage. This is usually attributed to wear in the timing cover and oil pump, which can often be addressed without disassembly of the whole engine. The TSM has instructions for measuring wear in the timing cover.

These engines also seem to suffer bad cam bearings pretty often; the bearings come apart (delaminate) and oil leaks back to the pan where it should not. You can also simply have a lot of wear in the bearings, but this is the same for all engines with this type of oil-suspended sleeve bearings. When oil pressure is really low, the rod bearings can lose their oil cushion and have metal-to-metal contact. You then have a knock which rapidly gets worse and signals the end of bearing life.

But if you've got good oil pressure and good compression, in general a rebuild isn't warranted. New timing chain and gears, measure and refurb the oil pump (lap the timing cover if needed), inspect the cam and lifters, replace some gaskets and seals, and you're done.

 

Thanks for the input. First the oil pressure when hot is pretty low at idle under 10#. I also get enough blow by that I get oil coming out of the fill tube and that makes a mess every where under the hood. I checked the compression a while back and #2 cylinder was about 15 to 20 lbs lower than the rest. While this is out for the ring gear replacement I was going to see what was good bad or indifferent to see where I need to go. While I was getting things ready to remove the engine I also saw that the plug from #2 is pretty badly oil fouled. Kind of making me think that the cylinder has issues. And since I'm not getting any younger I figured this was the time to do this so I don't have to soon anyway

 

Back when engines typically had forged steel cranks, garages would often do an "overhaul," usually including rod bearings, rings and valve grind. As I understand it, the main problem with a "freshening-up" procedure is the bore taper (existing wear) fatigues the new rings. Also, supposedly moly or chrome rings won't seat in an old bore, you're limited to cast iron rings which have shorter life. Modern engines (304 included) have a cast iron crank, which wears away faster than a forged crank. You could measure and maybe save an iron crank without turning it, but I would not assume you could slip in some new bearings and all will be well. Pretty sure that the modern cost of labor rules out this kind of repair over the typical factory-built reman engine. This is a much better job for a garage than any kind of overhaul; more profit and less liability.

How many miles on this engine? From your description, I'd guess that your rings are worn out. If you take it to a shop and have them measure it, I'm sure they will recommend straightening the bores and new pistons. You could go the patch-up route, as Donny suggests, and hone/re-ring but you won't get the same life from the new rings as the originals. That may be ok, depending on what you want from the engine.

If it were mine, I'd do the oil pump / timing cover recondition first and look at the results. Measure the gears end clearance, and hone the timing cover to set clearance at the low end of factory spec. Then run it and see what pressure you get. If the pressure does not come up to 20-30 psi, it's something you would need to do anyway. Also, the factory timing covers are much higher quality than the current aftermarket offerings, so by all means spiff up your original cover.

 

I'd also mention that, with the engine together, you can do a leak-down test that will point to where the loss of compression occurs. You can buy a leak-down tester, or there are online articles about making one. Requires a compressor, as I recall.

 

Thanks Tim. I got the motor out last night was an interesting proposition. I have a fiberglass tub and there isn't any clearance to get a wrench on the top 2 bolts had to cut 2 2" holes in the tub to get a wrench on them. I didn't want to try to pull the engine and transmission all together. I think I'm going to do pretty much the complete rebuild though. I'm still working at this point but after next year I'll be considering retirement and funds are available now and it is out so might be the time to just do it. My son wants me to do it as this will pass on to him when the time comes I can't still enjoy it. Might be when I'm 90 though lol

 

Ok question as well that I'm sure one of the group will know. Since everything will be nice and clean after the machining. Does someone know what the color of the block was originally? I am guessing blue but would like to match the original as close as possible and would like to know the code.

 

1972 blocks for California delivery were red. All the others were metallic blue.

Note that the engine enamel from the day was not so deep and shiny as what's sold today. I presume the engines were painted fast and - of course - not rubbed out. Also, haphazardly sprayed metallic can have quite a range of appearance, with more flake, less flake, gun angle.



This is pretty close, but I think it looks way too even and bright (ie the color was not as intense) compared to what I remember. Possibly more flake, finer flake? Or more pigment? Engine Paint Color preference Not as wildly shiny as some modern paints sold as AMC blue; less shiny like this is more realistic.

 

Thanks Tim I thought that was the color I could see that behind the flywheel

 

Ok another question Can the seal on the input shaft of my transmission (T15) be replaced without tearing that down?

 

I would not unless it were on the bench. Maybe you can. It's in the bearing retainer, and that's what holds the input shaft in the case. There is also a gasket between the case and the bearing retainer. Too much risk that the input shaft comes out and the pocket bearings go into the case.

Is it leaking? Gear oil smells very different from engine oil.

Thinking about it, you could maybe remove the top of the transmission and wrap some wire around the input gear to hold it back. Then you could remove the bearing retainer and replace the gasket and seal. It probably won't fall out on its own, since the bearing is pressed on to the input gear, and the bearing should be a fairly tight fit in the case.

 

I have the block, crank and heads at the shop now. Waiting on them to get it checked out to see what i need to have done. The shop guy said that there is a pretty good ridge in the cylinders and i pretty sure the heads do not have the hardened exhaust seats. So we will see. I think the crank will have to be ground as well journals had some scoring. I do think that this motor was opened on the bottom end or the crank was reground or replaced as the rod bearing were marked 010. Now just a waiting game on the shop I think there were alot of motors taken out because of all the time people were home with no where to go

 

Yes.

1 Remove the front bearing retainer without allowing the input to slide out. Hold onto the input shaft, tap the retainer loose, and slide it off. For bad angles or if I thought it would be a while before reassembly, I've used a small flat piece of metal with a hole drilled into it to keep the bearing in place. Just lay it across the bearing and retain it using one of the retainer bolts through the hole.

2 Replace the seal.

3 Reinstall.

Quite a simple job, actually.

 

OK so I did purchase a rebuild kit was asked about bearing and cylinder bore size. The crank is .010 under for size and the cylinders are .040 over. Why would you say available sizes on the cylinder are standard .030 .040 and .060 and then send me .030 pistons with .040 rings that won't work will it?

 

Has to be a mistake. They need to match.

What are you intending to do?

If I were having machining done, I would let the shop buy the parts. They can get a good price from suppliers and should be able to match the price of a kit easily. Let them pick parts that match their work (you'll still need to check all parts for fit at assembly). If they bore the cylinders oversized, they will need to fit the pistons to the bores. They can also exchange your crank for a reground crank with the proper bearings. If it's 10 under now, you'd get a 20 under crank and bearings in exchange.

 

Also, it's pointless to put new pistons in an old bore. You only need pistons if the bores are being machined to a new larger size.

 

Those are the sizes that they are going to those were what the shop said that they would be when they were finished. And I had planned to get new pistons I guess I'm going to have to send the kit back. I was going to be less to buy all of the parts that way. I guess thats what I get trying to have all the stuff in one package

They sent .030 pistons with .040 rings and I looked at the manufacture's site they don't even make 40 over