Weight groups, height groups, etc.

[Jay Auskin]

I'm rebuilding my 2.4L T motor due to a P.O. running on highly worn valve guides, and causing the #4 exhaust valve to break off and punch a hole in the piston, and give the top of the con rod a nice beating.

First of all, are the cylinder height group markings some sort of practical joke? 5 of the 6 are as close to passing for either a "5" or "6" height group as I've ever seen. But, I believe I have cylinders in the "6" height group, as one of them won't really pass for a "5". Anyone have real pics of both of these markings?

Second, I'm going to need to find a used con rod. Are there any markings on the rod to tell what weight group these are in?

Thanks in advance!

[BK911]

The cylinders have a triangle with a 5 or 6 in it. It should be in line with the other markings along the center of the cylinder.

The connecting rods have no markings to indicate which weight group they are in. Take them to you neighborhood drug dealer and borrow his scale. Clean them first though. Try to buy a new rod heavier than your old ones so you only have to grind one down.

Good luck!
BK

[Jay Auskin]

Is there also a casting identification of the height group on the cylinders?? The problem was I couldn't decipher the darn ink stamp markings of the 5, or 6 inside of the triangle. I think they're "6's" but I just like to be certain.

I owe my dealer money....I think I have a good scale at work to use.

[Tyson Schmidt]

From the Factory spec book for '72-'73:



Connecting rod weight groups.

Connecting rods are arranged in weight groups.
End digits of the spare part number indicate the given weight group.
The respective end digits are stamped into the shank of the given connecting rod if it was supplied as a spare part.

Weight:

over__under____weight___conn. rod__________conn. rod
grams_grams____group____part no.____________mark

645___654________1____911.103.015.31_______31
654___663________2____911.103.015.32_______32
663___672________3____911.103.015.33_______33
672___681________4____911.103.015.34_______34
681___690________5____911.103.015.35_______35
690___699________6____911.103.015.36_______36
699___708________7____911.103.015.37_______37
708___717________8____911.103.015.38_______38

Note

Connecting rods installed in a given engine must not differ among each other by more than 9 grams. To determine weight group, weigh the complete connecting rod without bearing inserts.






Hope this helps!

[Tyson Schmidt]

And here's the skinny on the cylinder height.

cylinder height (production)
#5________85.400 to 85.425
#6________85.425 to 85.450

cylinder height (replacement)

#R5_______85.150 to 85.175
#R6_______85.175 to 85.200


The cast-iron cylinders are ink-stamped on the barrel skirt. The birals are embossed on the area just above the skirt, but below the fins.

[cowtown]

Jay,
I am curious about how many miles/years it took driving on worn guides to cause the valve to drop. I've always wondered about this, just out of morbid curiousity.
Colin

[Jay Auskin]

Well, I believe it to be 51K miles. I bought the vehicle non-running. Take the valve covers off if you're concerned and look for carbon/soot on the cam housings. This will show if exhaust gasses are blowing by the exhaust guides.
My experience is on a '72 engine. I don't know if others had upgrades.