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Larry
Larry, Automotive technical expert
Category: Car
Satisfied Customers: 1139
Experience:  30 years automotive technical writer, editor & author
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I have a amc 360 engine in my 74 cj5, found the timing ...

Customer Question

I have a amc 360 engine in my 74 cj5, found the timing chain had jumped and that the cam, distributor gear was destroyed. new timing chain, new cam gear, and car starts ok cold, but after about 5 starts warm, engine wont start binds up...as if timing is way off, of which I know its not....can someone help... have had this problem for awhile now...
Submitted: 6 years ago.
Category: Car
Expert:  Larry replied 6 years ago.
By the sounds of it, I would say the cam bores in your engine block are probably out of alignment because the block is warped. When the engine gets hot, the alignment gets worse and binds up the cam. That's probably what happened the first time. The cam bound up and stripped the cam drive.

This happens a lot on overhead cam engines with aluminum heads (usually as a result of overheating), and sometimes it will even break the cam. It does not happen very often with pushrod engines, but when it does it almost always means the block has warped throwing the cam bores out of alignment. Somtimes this happens as the result of "aging" in the cylinder block, but the most likely cause is overheating.

One way to tell if the cam bores are out of alignment is to remove the cam drive, back off the rocker arms and remove the pushrods and lifters to see if the cam turns freely in the block. It may spin okay when cold, but the question is will is still turn freely when the engine gets hot?

If the engine is completely torn down, the amount of misalignment in the cam bores can be measured by inserting a straight edge in the cam bore and using a feeler gauge to measure the clearance between the straight edge and each bore. More than about .002 inches can cause trouble. The fix is to have the cam bores in the block align honed or bored to restore straightness.

Here's an article with more info on cam and crank bore alignment:

http://www.aa1car.com/library/2003/eb100338.htm


Customer: replied 6 years ago.
Reply to Larry's Post: I am understanding your reply, just wanted to say that the engine in supposedly rebuilt and now has about 2200 miles on it. Also I have not overheated it and have always constantly paid attention to temp guage operation..What you said about engine is making sense, but I'm very disappointed in engine I bought if this is true. The engine has that low mileage but is about 3-4 years old. So'll I'll be unhappy. It seems that after the last go around with replacing distributor with gm hei and new cam dist. gear it started 5 times fine when warm the sixth time it went back to its I don't want to turn over and was binding. Do you also think that there is possible other damage do to this. and is it a possiblity that the torgue may have not been done correctly, when installed...
Expert:  Larry replied 6 years ago.
Since the engine was recently rebuilt, another possibility is that the cam bearings do not have adequate clearance. Or, if an aftermarket cam was installed in place of the stock cam, it is possible the cam journals were not ground correctly and one or more of the cam journals are slightly oversized causing a bind with the stock-sized cam bearings.


But I would still think the most likely cause is misalignment in the cam bores due to block warpage. If this was never checked, it would be the engine rebuilder's fault.

The bolt torque on the cam drive would have no effect.
Customer: replied 6 years ago.
I'm back again, had to work today and I wanted to tell you that I understand your diagnosis and spoke to a few people and they kind of agree. let me give you a few more details. once when trying to start engine after hot got the binding going and the positive batter cable got hot actually started to smoke some. ok I cut off the end and renew and didnt have that happen again. A friend said the cable going from positive of battery is not beefy enough should have a bigger ought size. So I am going to replace that also.. But the thing I did tonite is I started it up cold. First crank alittle slow,but then fired right away..Battery showing 13.9 volts when I cranked I don't know what the draw was to starter...once the engine had run for 30 minutes up to temp and revved a few times, shut down and tried to crank after 10 minutes. was binding...Now what I did was disconnect battery and I had cranked the engine over about 4 full turn. it turned over very freely and only seemed tighter on the compression stroke...Does this seem to be that the direction we are going maybe that I am sending you in the wrong area...I really do appreciate your input, but what do you think....thank you again....
Expert:  Larry replied 6 years ago.
If your problem is hot starting, the fault could be one of two things: the starter is not getting enough voltage because the battery cables are undersized (replace with a thicker gauge size), the battery cables have a bad connection (remove and clean BOTH ends of BOTH battery cables), or something in the engine is binding up when it gets hot (could be warmped block, or could be insufficient clearance between pistons and cylinders).

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