SOHC 519

[rowdy58ford]

Dynode my engine Fri made 902hp 2nd pull 6800 rpm but gas idle pulley pulled threads out broke chain bent a few valves broke a few rockers pretty happy but sad for carnage.

[thatdarncat]

902 is real good. You have my sympathies though for the breakage. It sure seems like these motors can fight you every step of the way.

[Barry_R]

Great power.  Sorry about the breakage.  I have had that exact same failure.

A few things to look at.  I fixed and changed numerous things.  Never truly knew whether they were accumulative or one item caused it.

Take a very close look at chain alignment - mine was off.  With the timing sprockets, cam sprockets, tensioner and idlers all mounted to different surfaces with the rear cover plate and gaskets and heads its pretty easy to get things out of place.  I ended up milling and shimming to line everything up.

I have only broken two timing chains in 40 years of hot rodding.  One was in an OEM bearing test at Federal-Mogul.  One was my SOHC.  Both of them said Rolon on them.  If your's says Rolon throw it away and have the garbage man keep the can.

I think that the large bolt on my idler was bottoming out at full torque - might not have truly clamped in position.  A 9/16 bolt should still easily handle handle idler loads but I went to studs just in case.

[57 lima bean]

Not good to hear.Sad week for bio and mechanical losses.

[jayb]

Great power, Greg, sorry to hear about this issues.  Are you pretty sure that the idler pulley was what started the problem?  I think you may have had a chain break, and then lost that bolt that holds the idler pulley in place.  If the chain breaks, it can bunch up in the area of the timing cover and jam, putting some funny loads on the rest of the timing components.  Is the bolt bent at all?  Also take a close look at the front cover and see if it is cracked or broken around the boss where the stub cam comes through.

It may have been the idler pulley coming loose, though, those threads are notorious for stripping out.  In fact the same thing happened to Jason B's heads, and I'm going to put some helicoils in there this weekend.  Barry's idea for a stud there is a good one. 

Were you running that sheet metal intake on the engine?

[rowdy58ford]

yes sheet metal straight runners old intake maybe late 70 or early 80 off ebay wanted to se if it made more power than my cast alum dove looks so far that the bolt pulled out the treads 1/2 to 5/8 the bolt came from a iron head set up I'll  be sure to use all the threads this time over looked the bolt length still have to take a part the motor this is all  I know for now there was still more power to be had the vacuum pump sucked in the valve cover gasket  cork gasket was loose and did not put a tune on it yet next time.