The Stovebolt Site Forums The Shop Area Engine Shop 1948 Chevy Thriftmaster 3100 engine questions

I recently acquired a 1948 Chevy Thriftmaster 3100. It has had some work done to it, and I'm not sure if the valve cover is on correctly - or if it is even the correct valve cover for this engine (I've attached a picture).

Is this the correct OE valve cover for this engine? Does the valve cover look like it is on the engine correctly, or is it backwards?

Another question I have concerns horsepower output of the 216 inline-6 engine. The 1948-53 shop manual I have says the S.A.E. Horsepower output is only 29.4 for the 216 engine. However, most everything else I've found on the internet for the 216 says it is actually rated at 90 hp. Which is the correct figure?

Definitely not a '48 engine. Someone who knows better than I can decode the engine serial number from the machined flat area just to the rear of where the distributor goes into the block.

That appears to be a later 235 engine, not a 216. The 216 has a side cover that extends all the way up to the valve cover, with holes for the spark plugs. Also, the 216 valve cover is secured on with two studs extended up from the rocker stands thru the center with acorn nuts, and the oil fill cap is toward the front. Look for the build date casting numbers down by the starter and the casting code toward the lover right front of the block. Those will tell you what year the engine is.

SAE horsepower is based on the formula Cylinder Diameter squared times Number of Cylinders divided by 2.5. Also called Tax HP in some places. The 90 HP rating is a Brake HP rating, and what's used currently. It reflects the actual output of the engine.

BTW, I had some confustion on your other thread it with your location. I assumed it was Waterloo, Iowa, as I'm most familiar with that city. You might add the state to your profile.

Isn't the SAE 29 hp rating is measured at the wheels and the 90 hp is measured at the crankshaft with no accessories or anything attached?

You're thinking of SAE corrected HP that accounts for accessories. See my post above. I just added the formula used for the old SAE HP.

The cylinder head casting number is: 3835913

I can't find the block casting number, it isn't between the distributor and breather pipe hole and I don't see it anywhere else. The serial number stamped into the block next to the distributor is: 0392325F54Z

Wouldn't F54Z denote that is it as 1954 engine built at the Flint, MI plant?

That head was used on a 54 full pressure 235 engine but maybe was used other places
So the head casting agrees with 1954
-s

Yes, a 54 engine, but the Z indicates it was originally installed in a car. A 1/2 ton truck 235 serial number for 54 would have ended in X or U (with HD clutch) or M (with Hydramatic transmission).
The block casting number should be down at the front lower right near the pan.

Check out the picture posted in this 235 valve cover reply by member Pre '68 Dave.

Per his picture, looks like your engine has an even later 1959-62 valve cover on the 1954 head. The 1954 valve cover (center in his picture) has the oil filler in the forward position and also has 4 "slots" cut/formed (2 towards the front L&R and 2 towards the rear L&R).

Dan

The 29 hp formula is not related to engine displacement because it doesn't include stroke length.

Block casting number is 3835911. Attached are some pictures of the casting number on the front/right above the oil pan, and two pictures of the driver's side of the block.

This truck is also equipped with a 4-speed manual (1st gear is granny), so that has been changed as well. Still has a torque tube (enclosed driveshaft).

That 3835911 comes back as a 55 block, according to THIS.
A 4 speed isn't necessarily a changed transmission as they were available from the factory. If your truck has remnants of the 3 on the tree shifter setup, then it might have been changed from a 3 speed transmission.

Yes, the "F" confirms built in the Flint plant and the "Z" does mean Passenger Car.

Bottom line to verify what this engine was built for and original installed in is your given serial number (see the 1st pic below with a screenshot from the 1954 Chevy Passenger Car "Engine Serial Number" data) that decodes that number. The screenshot was taken from the GM Heritage Archive.

FWIW, below are additional screenshot pics from 3 different Chevrolet Parts Catalogs (1962, 1970 and 1971) that identify your casting number and the vehicles they were originally installed in. All total I found 6 different GM Part Numbers apply to the same casting number block depending on which vehicle it was meant for.

I know, way down in the dirt and weeds to include this extra info. But maybe it can be of use to you and others in 235 identification searches???

Dan

Can't thank everyone enough who have participated in this thread so far. Great information and it is certainly shedding some light on what I have in this old truck.

After a complete brake system overhaul, I've been driving this truck to more shows this year. One thing I have discovered is this 235 passenger car engine definitely doesn't have stock compression. It makes fantastic low end torque, and I'm getting detonation at heavy throttle around 1800 rpm on 90 octane ethanol free gas. Seems as though I need to rework the timing curve in the distributor's mechanical advance.

Do they make different weights and springs for the mechanical advance for these distributors? Or can I mix-and-match parts from something else/newer?

What is your initial advance set at?
I suggest that you start out by setting your octane selector at the center position mark and tighten up the 1/2" hex head bolt, then set your timing by loosening the clamp screw which is behind the distributor to 5 degrees BTD (On the BB) as a starting point.
Once you have established this factory spec, drive it up a steep incline and listen for pinging.
Pinging (detonation) is usually from too much timing. It can come from too much initial timing.
The beauty of having the octane selector is that once you establish the factory setting for the timing, you can make adjustments on the side of the road without worrying about going back to the factory setting without a timing light. Just loosen the octane selector bolt and return it to the middle mark.

Sorry it took me so long to respond to your question, had other things going on and this was put on the back burner. I verified with a timing light the initial advance is indeed set to 5 degrees with the octane selector at "0". If I set the octane selector indicator in the "retard" range, idle quality suffers a little but I still get pinging at heavy throttle around 1800 rpm. No pinging with less throttle or higher RPM. So, to me, it's acting like the mechanical advance is just coming in too soon and needs to be delayed.

Have you disassembled the distributor and inspected the advance weights and springs? It sounds like the weights might have rusted and stuck in the advanced position, or a spring has weakened over time, or broken. Can you turn the rotor clockwise with the engine stopped, and have it spring back? The advance weights and springs are accessible by removing the breaker plate, without taking the shaft out of the housing.
Jerry

I disassembled the distributor (removed the breaker plate) and verified the mechanical advance mechanism still worked (it does). Everything looks to be in good shape, moves freely, and returns back to normal position with the springs. Before reassembling, I moved the anchoring position of one of the springs (to an available hole in the cover plate) to give it better mechanical advantage over the centrifugal advance mechanism in the hope it would delay when the mechanical advance would come in. That seems to have worked; I don't hear pinging anymore and the engine sounds/performs better under acceleration.

I realize it would be better to find a proper set of mechanical advance springs, but I'm having difficultly finding one of those "kits" that would have the springs I need.