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Broke 390 FE timming chain, WHY?
I just put together a 390 FE engine. Nothing wild 9.5 to 1 pistons a flat tappet camshaft, single 4bbl, aftermarket intake, and all the rest stock. I drove it for about 100 miles with no trouble. It then quit and I discovered a broken timming chain and the crankshaft timming gear had all the teeth stipped off. the chain was still hanging on the cam gear. The break in the chain was in the part that was hanging on the cam gear. The chain was a stock type of chain with steel gears. The engine had plenty of piston to valve clearance.
What would cause this type of problem and what other damage might there be? |
I can only guess that it was an awfully cheap chain or one that was improperly heat treated, probably the latter. I've never seen the teeth completely worn off a steel or iron gear...wear, yes; completely gone, never. Sorry about your trouble; there's a good cnance you've got some bent valves because of this. I'd get in touch with the timing chain company...
Dan |
Doc,
You don't say whether this was a new chain, old chain, new timing set , single or double roller?? Old chain could be streched which would lead to failure New chain on old gears could fail due to worn teeth on the gears Installing a new set or any changes in the timing set could result in mis-alignment of the chain and or gears which could result in failure. Double roller more resistent to stretching than a single and worth the few extra $$ as insurance Also poor lubrication to the timing chain can result in failure. Also as Carnut mentioned you should check the valve train for damage and to insure that it's not dragging and causing the chain/gear to fail. good luck, Mike |
I've never seen one break, I've seen plenty stretch from age and get loose, way loose. Perhaps it WAS loose to the point where it 'snagged' on a tooth and THEN broke!
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Sounds like your cam locked up.
Did you get the block dipped and put in new cam bearings? |
timing chain failure....
Quote:
where the camshaft seized or in the case of a Triumph Dolomite engine where the jackshaft seized. ....Fred |
Lower gear is on backwards
Jerry |
Did you check gear alignment?
The FE`s normally had a different cam gear configuration than most aftermarket timing sets. Original OE installed cam gears were flat on the back (block side), and used a washer style spacer to control cam thrust movement. This spacer looked like a thick flat washer, with a slot in it, which allowed the camshaft dowel pin to fit into. Most aftermarket timing sets use a cam gear with a stepped section on the back, which fits inside the cams thrust plate, to control thrust. With this style of gear, the flat spacer MUST NOT be used, or it will cause the cam gear to stick out too far, and force the timing chain to work in a severe misalignment, as the cam and crank gears are supposed to be parallel to each other. Unfortunatley, some people are not aware of the differance in the cam gears, and also add the spacer. Is this possible in your case?
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I concur with the above 2 statments. The simple check is to install both gears without the chain, put a straight edge across them and look. They should line up perfectly. Lots of folks miss this as the build up seems so simple at this point. You can still check yours to see if that was the mode of failure.
Sorry for your problem, hope you get it running soon. |
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