Thread: Hemi??

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".........The Hemi's in the 55's had a real weak bottom end.
First sign of trouble is low oil pressure,before crank lets go....."

".........The 55 Hemi motors did not like to be ran at speeds in excess of 90 miles per hour for to long,,,,,"

I've torn a couple of the old Hemis down with thrown rods (and ruined cranks) it did/does happen. It was never a problem with the design or materials used in the bottom end, but rather the engine had been starved for oil. Run any engine without oil and it goes boom.

Keep in mind the 50's cars usually had relatively low rear end ratios and short 14"/15" tires resultuing in the engines spinning pretty tight especially at high speed. The cars that the Hemis came in were normally top of the line models with automatics and it is unusual (rare) to find a Hemi in front of a 3 spd/OD.

This is a picture of the oil drainback hole on a 55 331 Hemi head (typical of all the early Hemi Heads). There is one hole in each corner of the head. These holes are the ONLY way the oil that makes it way to the heads has to drain back into the oil pan. Normally when these are clean and the rocker shafts don't have excessive wear (the more wear the more oil that flows to the head) they do fine.

Now add several thousand miles of sludge build up in these holes (real common when running non-detergent oil), a little wear in the rocker shafts allowing a fair amount of oil to accumilate in the head (especially with the oil pump spinning at high RPM). Then just for grins say you starterd out 1/2 to a quart low on oil to begin with and chances are at some point all the oil from the pan is going to end up in those big valve covers. What happens?

"....First sign of trouble is low oil pressure,before crank lets go..."

It wasn't a "weak bottom end", but rather one that didn't get any oil. Of course the results are the same

What I would recommend to anyone who is going to test fire or run an old Hemi is to first pull the valve covers and and insure the drain back holes are clear. If your doing a rebuild, plug the bypass valve and go to a full flow filter system with a quality spin on filter. Keep the old HEMIrrhoids happy