Crane 753901 with stock 87 (help ASAP

Hey guys, I am having the crappiest day ever. I have been having problems with my rebuilt 4.0 I recently re-installed in the Jeep. So far it hasn't been anything major until yesterday. To cut right to the chase, I purchased the Crane Cams 753901 with the recommended anti-pump up lifters and springs that go along with the cam and installed them in the otherwise stock non-HO engine. I had the head and engine rebuilt with .030" Sealed Power pistons, but the machine shop re-used the old valves and re-ground them to the appropriate heigth (atleast thats what they told me). Anyway, I think a valve is bent as the engine is now starting to backfire through the intake on one of the cylinders. At first, I though the rockers were wore out and maybe caused a problem. Once I opened the valve cover I did indeed find about 4 very sloppy in tolerances, and I found 1 brand new pushrod bent. I replaced the rockers with all new, along the the new pushrod for the intake and exhaust for that cylinder. I started the engine again, and it still backfires, which leads me to believe that the intake valve is bent. My question is, what could have caused this to happen, the engine was run for about 2 hours until this happened, so I don't really think it was the cam's lift that did it. A mechanic friend of mine thinks the lifter failed and pumped up to the point where it ran the valve into the piston. Either that or the valves may not have been machined correctly. So, what do you think, was it the cam, the lifters, or the valves themselves. If the valve is bent, and i decide to replace all the valves, will the head need a new valve job or other head work? Please help!!!

Backfiring through the intake is a sure sign that one or more intake valves isn't closed during the exhaust stroke. The question is why? Here's a list of possibilities:

1. Intake valve bent or damaged.
2. Poor valve job and valve not sealing against valve seat.
3. Broken or dislodged valve spring.
4. Lifter stuck in fully pumped up position.

Your mechanic friend may be right. Whatever the problem is, you'll have to remove the head to find out what the damage is and how it could have happened.
More than 90% of problems that occur after an engine's been rebuilt are caused by mistakes in assembly rather than parts failure per se, so that's something to keep in mind when you fix the problem.
Did you check the installed height of the valve springs during assembly? The Crane springs install at a height of 1.70", and this requires you to machine 0.060" from the spring seats. Otherwise the spring tension will be too great, causing accelerated wear of cam lobes, lifters, bent pushrods, and rockers lifted off the head.

Check the cam timing (if you have a degree wheel), and at a minimum the index marks on the timing sprockets (and count the chain links with the tension on the chain as shown in the FSM). If you did not assemble the timing chain and cover, check this before operating the engine again.

It sounds like you may have the cam a tooth or more out of sequence, and the result may have bent a valve as you suspect (along with the pushrod and other loose things you found).

The other thing to check is the spring seats, as the Crane 258 AMC performance springs are usually a larger diameter from the factory springs and the head must be machined to provide a seat for the larger coil diameter. Failing to machine the heads may bind the springs, with the same bent pushrod result.

Dr Dyno, so in order for me to get my required height of 1.70" I must machine away .060" from the seats? What about the exhaust of 1.24", what must be done to achieve this? I attempted to find the installed height but couldn't find a suitable place to get a good measurement. I called Crane Cams and they set to check the lifter pre-load, which we didn't do. Another thing they said is that with the cam I got, the actual lobe part where the valves are not open is smaller than the stock cam, and I may end up having to buy slightly larger pushrods. Do you know the stock length of the pushrods, or maybe the correct size I may need? Thanks!

karter74 said:

Another thing they said is that with the cam I got, the actual lobe part where the valves are not open is smaller than the stock cam, and I may end up having to buy slightly larger pushrods. Do you know the stock length of the pushrods, or maybe the correct size I may need? Thanks!

Click to expand...

Mmm, that's interesting. So Crane cams are saying that the base circle of their cam is slightly smaller than that of the stock 4.0 cam. I'm in the same boat because I'm using a Crane 753905 cam for my stroker but I'm using Mopar springs (1.64" installed height same as stock) instead of Crane's. The stock pushrods are 9-5/8" long. The 1.24" that you mention is the spring length when the intake valve is fully open.
Here's the cam card:

http://www.cranecams.com/?show=brow...=243 C.I.&partNumber=753905&partType=camshaft

I'll have to phone the Crane cams techline to find out more info. about their cam base circle and which length pushrods to use.
I seriously doubt that your problems could have been caused by pushrods that are too short. If anything, I'd expect the opposite. Pushrods that are too short will not open the valves fully and cause poor performance, but not cause the kind of problems that you had.
Did you have the block deck or head surface milled?
You might find this article helpful:

http://www.cranecams.com/?show=faq&id=1

Something is wrong here. I did a stroker and used the Crane cam and the Crane performance valve springs without machining the head. I had the block decked .020 and used the thin Mopar Performance head gasket. I had the valve guides sleeved, but that has no impact on this issue. I used the Sealed Power H802CP pistons. I had no clearance problems and have 15k miles on my stroker. Sounds like a lifter pumped up and locked up.

There are a couple of different Sealed Power pistons that are used. Mine have a slight dish. Maybe the "standard" pistons do not have as much of a dish.

By adjusting the quench height, I run regular gas with no ping. Got to love strokers. I wouldn't change a thing on my stroker other than a high volume oil pump, but there are reports of a high failure rate on the high volume pumps.