Engine rebuild conundrum.

[Gumby]

I am doing a mild rebuild due to the motor having humped timing. So i have a bit of new parts to install, intake, cam, lifters, heads, pushrods, rockers, etc.

My question is do I have to replace the cam bearings and if so is there a way to do so without dropping the pistons and crank?

Thanks for any help folks.

[AwesomeJ10]

I'm 99% sure the answer is no, you cannot remove the cam bearings without dropping the crank.

In fact, I'm pretty sure that the average guy can't remove cam bearings - must be done at a shop.

[Addicted]

You don't need to drop the crank to do the cam bearings. You do need to pull the engine so you can replace the rear one. You also need a cam bearing tool to do the job. You'd be ahead of the game to pull it and take the short block to an engine machinist to have him do the bearings.

[Gumby]

I have the engine on a stand in the garage, this is my first rebuild. I have the bearing tool (no one i knew had one so i had to buy it). I am trying to save a penny here and there by doing all this myself i do not have a piston ring compressor. I guess if it comes down to it i could drop the crank to do the bearings. But is it a necessity to replace the bearings for a new cam. I hear of others doing cam swaps but never bearings.

[Addicted]

If the bearings look good it's not necessary. No need to drop the crank to do cam bearings. Since it's out and on a stand get to work. Just make sure you line the oiling holes up, take your time and you'll be good.

[fulsizjeep]

Martin, you should be able to inspect the bearings once you are down to no cam in the motor. If the bearings are not flaking off or worn down to copper surface, I would say don't worry about changing them. One indication of flaking bearings is small soft metal in the bottom of the oil pan and in the pick up screen. Have you dropped the oil pan yet?

[whsii]

If you are going to take the block to a mechanist, and have the cam bearings replaced, why not have the block boiled, cylinders honed or boarded, and do it right?

Yes it will cost more, maybe much more than you are thinking, but you will end up with something that will last and you will be proud of.

If I had to take an engine to the shop, I would have them mic the crank, check the bore, go through the heads, and balance it.

Yes it will cost $1K or so, but you will end up with a "new" engine. If you do the upper section as you are planning and drop a ring next week, it will cost you more in the long run. These things average 30 years old.

Balancing cost around $100 and is the best money spent in my opinion.

[Gumby]

Flint, I think there is copper showing on the front bearing. So i think it will be best to replace them.
Whsii, i am saving the cost on this one in order to have the 401engine professionally built.

Now i have to figure out how to get them out with the crank and pisrons still in.

I got home and took another loom at the bearing, there is no copper showing but it does show wear.

[FSJ Guy]

Again, you don't have to remove the crank or pistons to replace cam bearings. You may have to rest the entire block on a tire since the engine stand is likely blocking the rear access to the cam bearings, however.

[Mr. Goatman]

You don't say what kind of wear or mileage this engine has but if your that far into it already and the cam bearings are showing copper why not do the complete rebuild? It is a little more money now but will save more money and work later as well as give you piece of mind. Bearings and seals wear out. If the cam bearings are that worn what else is getting ready to die? If I had the engine out and torn down I'd be more concerned about the bearings and rings than the push rods or rockers. All of that being said; there have been times when I had more time and less money when I would tear down, fix what's broken, and reassemble. Just be prepared to do it again.

[tgreese]

Well, the OP states that he wants to keep costs as low as possible ... I presume he is only repairing the engine, not adding some go-fast parts.

If the engine jumped time, did the valves hit the pistons? If so, you should probably replace the pistons that contacted the valves. If not, then you likely don't need a whole lot of new parts. Normally if you have the heads rebuilt, you need to at least fit new rings. Most people would also replace the rod bearings if they need to pull the pistons.

I suggest you describe your whole project in a little more detail here. If you are doing a patch-up job, figuring out the minimum you have to do usually requires some experience. You don't want to overlook something you really need to do. Normally cam bearings are very seldom part of a patch-up job, unless you have low oil pressure. These engines can have bad cam bearings, but if you've been running a long time with very low oil pressure due to bad cam bearings, you really want to inspect and measure the rod bearings as well.

Does the cam have a flat lobe? Why do you want to replace the cam? What is your hot idle oil pressure and compression now? If you just jumped time, you likely want to just remove the timing cover and replace the timing set.

[jdaniel83]

I just did a cam swap in my '89 and I ended up having to have the cam bearings replaced. I pulled the motor and took it to a shop and had them do it, but they did it with the crank and everything still in the motor. It cost me a little more but it was much less then the cost of new rings, main & rod bearings, etc. that would have had to have been replaced had I pulled the crank/pistons. The guy at the shop said it was not too difficult of a job with the right tools, they just had to knock out and replace the rear cam plug on the back of the motor to get to the rear cam bearing.

[Stuka]

Well, the OP states that he wants to keep costs as low as possible ... I presume he is only repairing the engine, not adding some go-fast parts.

If the engine jumped time, did the valves hit the pistons? If so, you should probably replace the pistons that contacted the valves. If not, then you likely don't need a whole lot of new parts. Normally if you have the heads rebuilt, you need to at least fit new rings. Most people would also replace the rod bearings if they need to pull the pistons.

I suggest you describe your whole project in a little more detail here. If you are doing a patch-up job, figuring out the minimum you have to do usually requires some experience. You don't want to overlook something you really need to do. Normally cam bearings are very seldom part of a patch-up job, unless you have low oil pressure. These engines can have bad cam bearings, but if you've been running a long time with very low oil pressure due to bad cam bearings, you really want to inspect and measure the rod bearings as well.

Does the cam have a flat lobe? Why do you want to replace the cam? What is your hot idle oil pressure and compression now? If you just jumped time, you likely want to just remove the timing cover and replace the timing set.

AMC V8's are non-interference engines. So even if the chain broke completely the valves and pistons would be fine.

As for the original post asking if you can change cam bearings without pulling the engine, the answer is no. Engine has to be pulled in order to get to the back half of the cams bearings.

[Gumby]

Thanks fellas I will knock out the plug and carefully remove and install new bearings and a new plug. I had an issue with the original motor when it jumped timing I found the chain to be loose very loose. loose got a deal on a replacement motor with all intention on rebuilding the original. I finally took the heads off and found that the motor had been rebuilt and is bored .30 (stamped on the piston face). I got a sweet deal on a set of rebuilt heads valve job also completed and has double springs, the owner was planning on installing them on his 360. This is what made me decide to do the modification. I have no idea when it was rebuilt ( the engine), the mileage was just over 178000. So I am here with my dilemma. I really know nothing about the pressure readings prior, never really got to drive it much. The previous owner could not keep it running. running got it going good then it would have issues then it jumped timing so I pulled and replaced the motor.

[Addicted]

.
AMC V8's are non-interference engines. So even if the chain broke completely the valves and pistons would be fine.

Tell that to my '71's 360 with the bent exhaust valves from the timing jumping from a stretched chain.

[Stuka]

.
AMC V8's are non-interference engines. So even if the chain broke completely the valves and pistons would be fine.

Tell that to my '71's 360 with the bent exhaust valves from the timing jumping from a stretched chain.

Did it have the factory dished pistons?


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[Addicted]

.
AMC V8's are non-interference engines. So even if the chain broke completely the valves and pistons would be fine.

Tell that to my '71's 360 with the bent exhaust valves from the timing jumping from a stretched chain.

Did it have the factory dished pistons?


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Yup.

[Addicted]

.
AMC V8's are non-interference engines. So even if the chain broke completely the valves and pistons would be fine.

Tell that to my '71's 360 with the bent exhaust valves from the timing jumping from a stretched chain.

Did it have the factory dished pistons?


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Yup.

[babywag]

My 401 '77 Cherokee bent valves when the nylon coated cam gear let the timing jump.
(100% stock engine)
It can/does happen when they jump timing.

[Stuka]

Well I stand corrected


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