VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 Checking cylinder pressure

I am working on a 216 out of my 1940 Business Coupe.

I ran a compression test and had an average on all cylinders, (with spark plugs removed) of about 110 except in the front cylinder which was 90. I removed the head and had it surfaced and reinstalled with a new head gasket. I redid the compression test and found the average pressure was about 35 psi. Adding oil to the cylinder has no effect
I removed all the pushrods to elimate valve issues with no change.

I systematically reinstalled the sparkplugs and found the cranking speed slowed until it virtually stops with the last plug installed.
All three of the compression gauges give roughly the same readings.

I have been using 12 volts to spin the engine. The starter is 6V and has just been rebuilt.

Any suggestions?? Comments??

Thanks,

Mike

The exhaust valve is leaking (burnt) for #1.
Was normal to grind valves on those engines every 35,000 miles or so.
This is assuming the valve was not sticking.
You should of had the valves ground while the head was off.
Super low compression with all valves closed because it could not breath.

Is it possible to resurface a head without disassembly? I wouldn't think a reputable machine shop would do such a thing. Also I have never heard of doing a compression test with all the valves closed. What information would such a test yield?

Yes a head can be resurfaced without taking the valves out. Depends to the reason it is needed.

It is diffficult to believe the engine would even turn over with all the valves closed.

Re resurfacing the head: So I would think that all the installed valves would be in the way of bolting the head down on the machine. Further to that, if it were my machine, I would not be putting a head complete with engine grime into my machine to do the job. Also with all the flying debris created during the grinding, I can't imagine how one would guarantee that non of it would be staying in the head.

All the machine shops I know CAN machine heads with valves installed but they dont like it apart from the grime and some wont they claim (and I wont disagree with them) that the machining debri cant be fully removed from previous grime.
Tony

I don't understand how the compression could have been less after the head planing than before. Something strange is going on. Were the bolts torqued and in proper sequence? Mercy. Hurts me head to even thing how this could happen.

Charlie

It was less after because it was checked with no push rods installed which menant all the valves were closed. This prevented "compression" from entering or leaving the combustion chamber.

"I redid the compression test and found the average pressure was about 35 psi. Adding oil to the cylinder has no effect
I removed all the pushrods to elimate valve issues with no change."

Gene,

Sorry. I took the above statement as Mike's sequence to again take the compression. Thus the same way that as that when he got the 90 - 110 lbs.

I thought this retest was before came before the pushrods were removed.

Charlie

I took the head back to the machine shop and it was determined that it was in poor condition. Apparently the valves had been redone a number of times and the best solution would be to find a new head.

Question? Will a head from a 1941 216 swap out with one from a 1940?

Thanks for all the input,

Mike

Due to the fact the the 1940 had domed top pistons a 1941, which had flat top pistons, will not work.
I know of a new 1937-1940 head that may be avaiable.

If the valve seats in the head have been ground a number of times why not put in new seats? Not really necessary due to lack of lead in fuel but the hardened seats can give a head a new lease on life.

First, I am all fore saving the head, but the shop said that it is so bad that putting in new seats would risk cutting into the water jacket. The existing Valves are sunk into the existing seats. If I want to risk it, ok, but they will not be responsible. The valve springs are very weak and the valve themselves are very thin.

The pistons are flat topped alum pistons which leads me to believe that it was rebuilt at some time. There is no ridge in the cylinders. The engine number from what I can tell, indicates a 1940 block.

Further comments would be appreciated.

Could you send me info on the new head?

Thanks,

Mike

If it has flat top pistons you can use a 1941-1953 216 head.
What is the casting numbr on the lower right side of the block> If it is 839132 it is a 1940.

The number from the block with the bad head is
839132 as you suggested.

The head I am currently looking at comes from a block number
3835794 which seems identical to the first.

Mike

3835794 block is a 1952-1953 216.
To use that head on a 1940 you will need to use the 1941-1953 216 rocker arm assemblies as well as the valves. All the gaskets will fit from 1940-1953 216.
The heads also have a casting number on top Would be under the valve cover.

If you were to use a 1940 head with the flat top pistons you will end up with a very low compression ratio.
Check the pistons with a magnet. If the magnet does not stick they are aluminum indicating the engine has been rebuilt at some time.

So just to clarify, the 1940 engine # 839132 has flat, aluminum pistons and there is no ridge in the cylinders, but it has a bad head. I assume the engine has been rebuilt.

The 1952-53 engine # 3835794 has flat, non-aluminum pistons and there is a ridge in the cylinders indicating wear but the head has a good casting but needs rebuilding. I have not checked the lower end.

Can/should I rebuild the head, rocker arms and all, from the 1952-53 engine and put it on the 1940 engine??

Is it better to find another 1940 head and rebuild and use that one??

Is there an advantage to rebuilding the 1952-53 engine and using that engine?

I tend to keep things original as possible hence, if needed,
Is the 1940 head you referred to available??

Again, comments are appreciated.

Thanks

Mike

If your original engine as flat top pistons they are incorrect for a 1940 head. The combination of flat top pistons and a 1940 head will give a very low compression ratio.
In 1941 they went to flat top pistons and a very different combustion chamber and valves. The 1952 head with your flat top pistons will give you a 6.6 to 1 compression ratio.
The 1940 engine with domed pistons and 1940 head had a 6.25 to 1 compression ratio. The new and improved 1941 head raised the orse power from 85 to 90 HP. Bening a 1952 head you will be up to 92 HP.

Yes, if it were mine I would rebuild the 1952 head and rocker assy.
There is no big advantage in installing the 1952 block + a rebuild will run far north of $1000.......

If you use the 1940 head it will be necessary to replace the flat top pistons with domed pistons or you will have about a 5.00 to 1 C.R..
I have the new 1940 head. It sat it a damp area and one end has surface rust that the shop would have to blast off. Then you would need to get all new 1940 valves, etc
The shipping of the head would probably be $65 + dollars snd I would like to get $100 for the head.

So there is something missing here. The original compression numbers were all 110 except for one cylinder that was 95. So I assume that that was with the flat top pistons? By the way those numbers are not too shabby.