[Importtech]

Hey guys one of the guys I circle track race with is having a problem with timing chains breaking. It is a 355 and I know his is running an ISKY 278 hydraulic cam .450 lift 234 @ .050 on 106. I think it has happend 3 times. I know he tried using a cam button which I'm thinking he shouldn't need anyway since it is not a roller cam. I'm thinking there must be a problem with his block but not really an engine man. Can you throw some ideas our way? thanks in advance.

 

[Guest]

Gears out of alignment.

 

[Just_Another_Mike]

I had a motor which, before it was run, noticed that the rear cam bearing plug was in too deep. This would have caused the gears to be out of alignment as the cam would have been too forward and it would have worn the rear plug as well. It was a mild motor and would have probably run(for awhile at least). Just an idea.

 

[bbpwr]

next time he has the cover off take a 12 inch straight edge or a steel ruler and check to see if the gears are flush with eachother. then id check cam endplay. after that id maybe begin to suspect a slightly bent crank snout like mike said to check the cam plug .

 

[ironhead]

Jack..is the timing chain actually seperating?I only ask..because a chain break would result in major engine damage and most likely require a complete rebuild if not replacement.

 

[JimM]

Jack..is the timing chain actually seperating?I only ask..because a chain break would result in major engine damage and most likely require a complete rebuild if not replacement.

my thoughts exactly. How lond did it take him to dag the valves out of the pistons?

 

[71malibu406]

same thing i was thinking as well since i broke a timing chain a few months ago in my 331 Ford and it bent 14 valves and damaged 2 pistons and i wasn't really even on it that hard. still haven't gotten it all back together yet.

 

[Importtech]

Thanks for the replies...Yeah he's definitely bending valves and maybe getting pistons not sure on that but I'm sure its getting in his wallet. I'll get him to look closely at the gears alignment. I havent seen the engine but I'm under the impression the chain is breaking and not the cam gear. I've seen teeth come off the cast iron gears before.

 

[ironhead]

Jack..have your roundy round buddy check his piston to valve clearance.Check this 10 degrees both sides of tdc during the overlap period.The chain fail may be a result of slamming valves into piston tops.The P/V clearance and valve float with a hydraulic cam all lead up to bent valves and the shock transfered thru the cam to the chain link.

 

[Tom Mobley]

tell him to dump the thrust button, he doesn't need it with a flat tappet cam.

Has he got one of those needle bearing thrust washer deals behind the upper timing gear? You have to relieve either the upper gear or the front of the block the thickness of bearing or it will push the cam to far forward and stress the timing chain.