There has been considerable controversy on whether or not the 3.0 L 12 valve engine is a valve bender even though it is listed as non-interference. I truly donÆt have the answer and I have heard opinions and testaments going both ways. I just had an interesting conversation with an automotive machine shop owner (Bill) this morning. For what it is worth, here it goes. About ten years ago, this shop was contracted to machine the heads of a dodge caravan 3,0 L 12 valve that had leaking head gaskets. (External) He claims that he machined the heads approx. .020. The shop installed the heads along with a new belt and water pump. About two months later, the water pump seized and the belt broke which resulted in some bent valves. (He did not remember how many and which valves) The shop offered to repair the head, belt and pump problem but the vehicles owner wanted a new engine and would accept nothing less. The owners sued the shop for faulty work, the pump manufacturer for defective part and the machine shop for machining the head in excess of factory specifications. Bill had the heads and attempted to find a combustion chamber volume specification. He was unsuccessful. So, he did something that I thought was pretty unique. He obtained a head from a low mileage engine that had not been touched and he replaced the bent valves in one of the heads that failed and took them to the shop where the engine was. Modeling clay was put on the top of a piston. The heads were installed one at a time without a head gasket. The cam was rotated with first an intake fully opened and then an exhaust. The engine was rotated by hand while each valve was set at full open. He claims, there was only.018 difference of valve depression between heads. Now the real interesting part, he told me the final clearance between the valve and the piston was .007 on one head and .025 on the other. I understand this is without a head gasket but scares me. Can anyone with a 3.0 confirm this? By the way, Bill said after all his research, the insurance companies decided to settle out of court with each sharing the cost of a new engine.
Conner

No on has been able to confirm much of anything.I am wondering the same thing since I just broke a timing belt but the majority think that it has probably done no damage.

Conner -

Very interesting information, but if I'm reading the FSM correctly and I was the judge or plaintiff, I'd have made your friend buy me an engine all by himself and let him deal with the water pump manufacturer for the price of a water pump and associated labor to R&R.

The FSM states the service limit is (-) 0.008" total including any milling to the deck.

On my rebuild I had a total of maybe 0.004" removed.

I do believe the valvetrain crashes on these engines are the result of overmilling the block and heads, but it's just my opinion since I haven't seen nearly as many engines as professional mechanics.

Frank

Frank: I agree with your specs, but we all know that has been exceeded many times over. What i am attempting to do here is get handle on the problem so that we can safely say. Dont worry about it or you may have problems. I am sure there are many heads out there that have been machined several times. How would you know without special equiptment? Using Bill's measurements, i can see how a replacement piston,connecting rod, head gasket thickness or a cam change could make a big difference. This does'nt consider how many times the head was machined. My point is the clearance that tight to begin with? I dont know.

I may be a fuss budget, but I "pre-assemble" the engine and check piston clearances with modelling clay. I then assemble the engine and rotate it by hand to recheck with the plugs out, then spin it with the starter to pre-oil it and one final check. I didn't do it that way once on a maxi dollar SBC, and once was enough.... It's amazing how much damage one busted sodium filled exhaust valve can do.

The overall cylinder head height is listed at 3.31" with the milling limit not to exceed 0.008" including milling to the deck. A machine shop should be able to check the head, although afaik they can't determine the block milling depth for total accumulation other than what they do at the time. The modeling clay method that your friend used is the time-honored way engine builders check valve/piston clearance, but I guess otherwise the factory service limit should be followed. It should be easier on blocks you know haven't been rebuilt, but the age of our trucks is getting to the point that multiple rebuilds and a long chain of ownership complicate the circumstances.

Maybe it would be a good idea for the next one of us who does a rebuild to use the modeling clay to get some overall measurements for definite clearance requirements. It should be easy to then measure piston/deck clearance and overall head thickness and come up with a total limit for use in future rebuilds.

Good thinking! <img src="/forums/images/graemlins/kewl.gif" alt="" />

Frank