CAM WALK

[wjtom]

My question being why do these motors need the pin in the first place.There a plenty of motors that just use the timing chain and taper on camshaft to keep the cam where it belongs. Thoughts anyone?

[SilverXJ]

The timing chain does not do much to keep the cam in the block. The taper on the cam lobes along with the pressure from the oil pump drive should keep the cam in the block. There are some Ford flat tappet engines that have a cam retaining plate as well. A certain Ford 302 comes to mind. We had one come into the machine shop when I was still working there. When I heard the sound the owner was complaining about i knew exactly what was happening. I found that a mismatch of parts gave him cam walk.

In our engines, the early 4.0L had no cam retention mechanism. Later Jeep added the spring and pin to the cam bolt. There is also an AERA document referencing rebuilt engines with a knocking noise that was coming from cam walk. The rebuilder omitted the pin and spring. And, as you know, Jeep later changed the pin and spring to a retention plate. I don't think this was done as a "might as well", but they may have found an issue some where. Perhaps under certain circumstances Jeep found that the pin and spring wasn't sufficient. Which, in our case, is exacerbated by out valve train and cam modifications.

However, I have no answer as to what causes the cam walk to begin with. This is a question that has plagued me since my cam bearing failures. Oddly enough it seems that after my failures others have had the same problem. The only thoughts I have are a) that there is some kind of pulsing going on in either the cam/valve train or the oil pump that is loading and unloading the cam or b) perhaps the timing sets we have been using don't put the gears inline with each other and perhaps the cam gear is more reward than the crank gear, which could pull the cam out of the block only to be sucked in later by the cam lobes and oil pump. I know its not a high volume vs standard oil pump issue. Another observation I have found is that the 4 cylinder version of the 4.0l came with an actual chain tensioner on the slack side of the chain (passenger) where the 4.0L had the snubber block on the tension side of the chain. That also leads to the question why would the 4 cylinder need the tensioner and the 4.0L got the snubber on the tension side of the chain. A logical explanation of the snubber on the 4.0L would to prevent the chain from slapping the timing cover. But then why would the chain be slack enough to slap on the tension side? The only other off the wall though I have is that the waster spark system (coil rail) is causing some kind of havoc on the exhaust stroke.

[wjtom]

So basically nobody knows.I have had no problems yet.But with the amount that do it would be interesting to know the reasoning behind the changes over the years.It would be nice to see somebody make a timing set and cams for the later model stuff with the cam retaining plate.Roller would be real nice but if nobody asks it wont happen.Crane has the stuff but broke the tool for cutting the cam gear.Guys you have to call and ask so they know theres a market.Otherwise we are stuck with what we have.They had the stuff over a year ago.

[SilverXJ]

I know of no one to ask about this. I wish I did. While my stroker is running well I feel like I fixed the symptom, not the cause.

Jones Cams will make a custom cam based on the later blank. I'm sure other small grinders will as well. Jones was just the first one that said he is able to and he has a very good reputation so I stopped with him. Jones also said he could make me a roller cam... but it was ~$1000 just for the cam. I am completely happy with the Jones' cam in my engine. But timing sets there is nothing but the stock style one which I am running. I do recall a post about using a ford something or other timing set and having some machining done to it to make it work for the 4.0L.

I spoke with crank last year or the previous year and they said they were working on a roller cam. I may call them again to put a bug in their ear.

[wjtom]

I know of no one to ask about this. I wish I did. While my stroker is running well I feel like I fixed the symptom, not the cause.

Jones Cams will make a custom cam based on the later blank. I'm sure other small grinders will as well. Jones was just the first one that said he is able to and he has a very good reputation so I stopped with him. Jones also said he could make me a roller cam... but it was ~$1000 just for the cam. I am completely happy with the Jones' cam in my engine. But timing sets there is nothing but the stock style one which I am running. I do recall a post about using a ford something or other timing set and having some machining done to it to make it work for the 4.0L.

I spoke with crank last year or the previous year and they said they were working on a roller cam. I may call them again to put a bug in their ear.

I spoke with them late last year.They broke the hobbs tool for cutting the distributor gear.If nobody calls it gives them no incentive to spend the money.Come on guys the advantages to the roller are worth the extra money.Yes the upfront cost is more but there is no downside.Now if we can just get someone to make a roller to use the cam retainer and have a good timing set.Lots of guys starting to push these motors with blowers and turbos.Same goes for edelbrock with a head thats reasonably priced.They did the research and know how to make it in their foundry but didnt think the market was there.Scat beat eagle to the punch even though eagle was poking around and came up with a complete kit first.Pick up the phone or shoot an email to these companies show them theres a market.Eventually the used stuff will dry up like everything else and get expensive to the point the new stuff looks really attractive.