VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1912-1928 Engine swap vs adding a 1928 head to a 1921 engine

I am finishing up the rebuild on a 27 block with 28 head. I have the correct (28) rocker arms, so geometry is all ok, HOWEVER, neither 27 (too short) or 28 (too long) push rods will fit. Anyone know what correct length of push rods should be for this modification?

This is concerning....

Please keep me abreast if you discover the solution. I only have the rods from the 1927.

Thanks.

Just a seat-of-the-pants-engineering thought:

1. On a compression stroke for a particular cylinder, put in a '27 pushrod (with end cap) and adjust the rocker adjustment screw to half its travel.

2. Measure the gap between the top of the valve to the valve surface on the rocker.

3. Add the measurement obtained in step 2 to the length of the '27 push rod and that is the total length of push rods that you need.

4. Either make new push rods, shorten the '28s, or shorten the valve stems.

Cheers, Dean

Thanks to all who offered help on my question about pushrod length for a 28 head on a 27 block. Here is how I finally solved the issue.

I made an adjustable pushrod gauge from some threaded rod and a small bit of pipe that the rods (two pieces with locking nuts) could slide in. With this adjustable device I could shorten or lengthen the gauge til I had what seemed to be the best fit. My result: required length - about 10 5/8 or 1/4 inch longer than a 27 rod (which is 10 3/8).

I cut the ends off of some 28 pushrods, rounded the ends (but did not harden the cut end) and placed this cut end in the cups (top end). Got advice to place hardened ends in the tappets. Not sure how well these will hold up, but we'll see...

Thanks again. Great to have some experts just a blog away.



Dave

Why not try to harden them? Just heat till cherry red and quench in oil. Hit with a file will tell if hard.

The push rods are normally hardened about 3/4" from each end.

I was at the machine shop today, it was a virgin block. So it was bored .030 over and it's like new. We ordered the engine kit from EGGE. The crank will be sent out early next week.

The machine shop found a guy to make the bearings. He collect all the stuff. I was trying to get "cheap" with it by reusing the rods. He called me a few days later and advised I had three of one (351663) and one of another. Of course the odd one had a cap that didn't marry well with the rod besides the fact it weighed more. Amazingly, after some shopping I found a cap and rod that matched the other three for $25.00. It arrived today. I'm getting closer.

Well, after several years I finally got the engine back and it is currently sitting the car.

I did not have to modify the rods to accommodate the 1928 head. The rods from the previous setup worked fine and everything was able to be adjusted.

I moved earlier this year and in the move things were misplaced. So, I purchased a RAKXO to replace the one I lost; expensive lesson. Additionally, I had the 635B distributor refurbished.

The only remaining item directly attached to the block I need to replace is the water pump. The oil-pump, when tested, was able to pump mineral spirits, so I decided to leave it alone and reuse it.

I am currently battling with locating the proper spark plugs. I purchased Champion W89D plugs and they do not fit. It appeared as though the spark plugs were threaded differently. Also, several other plugs listed as replacements for the Autolite 3077 were not even close. Looking for assistance with this matter.

I am also battling with the pressure plate. I had to disassemble it when I originally took it out. Most parts I can find someone who refurbishes them, like the cam and such, but I have had no luck with this particular piece. So, I'm also looking for someone knowledgeable to send this part to so they can fix my handiwork.

Thanks,
David

All 4cyl Chevs use the same spark plug thread diameter and thread pitch,which is 7/8" diameter X 18 threads per inch.
Perhaps you need to run a 7/8" X 18 TPI spark plug tap through the threaded holes in your cylinder head,as they may be full of dirt/carbon etc,or have damaged threads.

Hi David,

I had a 26/27 head which had apparently been manufactured in the 30s as a spare part for the earlier cars which used modern sized 14mm spark plugs. Perhaps you have one of these? The thread on these is a smaller diameter than the original plugs.

Frank.

Hey David,

Good to hear that you are making progress!

I have two '28 engines. One has the 3077 plugs and the other has W89D. Both plugs have the same threads (7/8-18).

Are your spark plug holes larger in diameter or smaller than the W89D threads?

If smaller, I suspect that the previous owner of your '28 head put adapters in the holes in order to use a more modern plug. You might be able to see whether an adapter is in there by looking at the holes from the cylinder's side (as if the pistons were looking at the bottom of the plug).

Below is a picture of a tool that I made from an old spark plug to chase the spark plug threads in the engine that I'm rebuilding for Lurch.

Hope this helps. Dean

If the cylinder head has either spark plug adaptors fitted or the plug holes were drilled & tapped for smaller thread diameter & thread pitch plugs,you'll have fun trying to find a modern plug with enough reach toward the combustion chamber,as well as the correct heat range.
If it has adaptors take them out and fit 7/8" plugs,or if the spark plug holes are drilled and tapped for smaller more modern plugs,get them machined & tapped to the correct size.

Thanks for the reassurance. It was the plugs. The first plug, and another, have factory defects.

This morning I checked the threads in the cylinder head and they were in great shape; no debris or burs. After trying to thread the spark plug into all four spots, I unboxed another one. I was able to thread the second one all the way down in all four cylinders. This was also the case with the third. However, the last one I was only able to get about halfway in all the cylinders. So, I'll have to send those two back.

Thanks for the help. Now I just need to get the pressure plate sorted out.

Instead of returning the plugs with the "oversize" threads,why not try running a thread file(thread restorer)over them first?Might save time & a few $$$