The Stovebolt Site Forums The Shop Area Engine Shop Got a call from the machine shop UPDATE

The cabbage was clincher.

Carl's former cylinder head is now a resident of my shop, where it's going to get a full rehab, including oversized intake and exhaust valves and some minor port reshaping. It's going to find a new home on a highly modified 261 I have on the drawing board. Putting 1.94 inch intake valves for a Powerglide-equipped spray oiler 235, and 1.6 inch diameter stainless steel exhaust valves for a small block Chevy V8 puts the valve seating area out into a fresh area of the cylinder head where valves have never been seated before. It takes a lot of metal butchery that the average machine shot can't (or more accurately WON'T do), but the results can be pretty impressive on the dyno. Thanks again, Carl, for donating that head to the cause!
Jerry

Donating?! I skinned you alive on that horse trade. A chicken sandwich, and you let me supersize the drink and fries.

Got Sweet Pea all back together. She wouldn't start. No spark.
Had voltage at the voltage reducer, fore and aft.
Had voltage at the coil at the "+" and "-" lugs.
Had voltage at the distributor.
Had voltage at the points.
No spark when manually opening the points. BINGO.

Burnished the points with a business card and got spark while opening the points.
Put the cap back on and she started right up.
Brand new everything on that 848 head. Valve seats, stainless steel exhaust valves, new intake valves, new valve guides.
This engine has never run smoother.
A plan has come together, finally.
The best advice which was offered on this thread was, "Find another machine shop." I did. Thank you all.

That's excellent. And you're welcome.

" I love it when a plan comes together!" Enjoy the ride!
Jerry

Great news! Thanks for the wrap up!

Moral of the story.
Make sure that your machine shop knows their stuff about these old engines, or are able and willing to do the research.
In order for you to determine if THEY know their stuff about these engines, YOU need to know your stuff so that you can ask the right questions.
I did not ask the right questions and it cost me $1800 for a second rebuild caused by a broken connecting rod, likely caused by too much compression from the machine shop not knowing what the specs are on the head thickness of a 235.
The second rebuild lasted 3,000 miles before the valves were cooked by overheating in the combustion chamber from too much compression and absence of a quench trench. I am lucky that I did not break another connecting rod before I pulled the head looking for why I had a bad miss on the #1 cylinder.

I will be truthful, I agree that the first shop totally and completely messed up the head. But I think there was more to it then just a little extra compression. I think they really did not know what they were doing over all and all of it contributed to the failures. Really happy to hear you have it all sorted out and running well!

Once I get the new oversize valves fitted (properly) to the problem head, it's going to be interesting to do a CC test on it and calculate the static compression ratio when it's combined with a "261" engine that's actually going to approach 300 cubic inches. The "more is better" approach to compression is sort of a myth, since a lot of people don't understand WHY compression is increased on a high performance engine. When a radical camshaft is installed into an engine, it gets that extra power (only at high speed) by keeping the valves open longer- - - - -opening earlier, and closing later. In the case of the intake valve, that means that a good portion of the compression stroke happens before the valve closes. It's impossible to build up compression pressure in a cylinder with a valve open- - -even slightly. So- - - -if you want to get the compression pressure back up to where it was on a stock engine- - - -you've got to squeeze what's left of the cylinder harder. That requires a dome on the piston, and/or a smaller combustion chamber- - - - -JUST TO GET BACK TO SQUARE ONE!

Increasing the compression ratio without installing a radical cam approaches a situation where spark plugs aren't required- - - -better known as a Diesel engine! Most gasoline engines aren't built to survive that kind of abuse!
Jerry

During a "normal" engine rebuild where the cylinders are bored over .0030 or .0060 due to normal wear and tear, how does this affect performance since the factory camshaft is usually installed.

A Chevy 350 bored .030" oversize goes to 355 cubic inches. That's 5/8 of a cubic inch per cylinder increase in volume. For all practical purposes, the increase in compression can be ignored. There needs to be a big increase in bore and/or stroke, or a dramatic reduction in combustion chamber size to make a big difference in compression pressure. That same 350 with a 76CC cylinder head has about 8.5:1 compression. A 64 CC head brings it up to around 9.5:1 or maybe 10:1. Domed pistons and a 64CC head approach 11:1.

A Chevy 230 six has flat top pistons. A 250 has a 1/4" dish in the piston top and uses the same cylinder head. That's a difference of slightly under 4 cubic inches per cylinder, from a longer stroke on the 250. The dished piston is there to keep the compression the same on both engines. Running a flat top piston for a Chevy 307 V8 in a 250 brings the compression up to about 9:1.
Jerry

Thanks.

My engine was bored .060" over, and there is .050 missing from the bottom of the head, leaving most of the quench trench by the intake valves missing. The machine shop also put in all new valve seats at an unknown level. If the new seats were ground too shallow, compression would be even higher.
I did a hot compression check on all cylinders before I pulled the head, #2 through #6 were at 240 PSI (+/- 5 PSI), and the #1 with the leaky exhaust valve was at 180 PSI.
That is about 100 PSI too high. Its a brand new gauge. I doubt that the gauge is off by 58%.

When I do some major metal butchery on that head- - - -bigger intake and exhaust valves, recessing the intake valves back to the proper depth, opening up the combustion chamber around the bigger exhaust valves to unshroud them, and a few other kinds of metal butchery- - - -I'll have one of two things- - - -a really good-performing head that can be paired up with a pretty radical cam, or a boat anchor! I won't really know until I'm about 75% of the way through the job. If I end up making the head worse than it already is- - - -no big loss, as I can use the new valves in a different head if that one can't be salvaged. I've got a few other sneaky tricks up my sleeve for the engine, other than the cylinder head mods I've mentioned.
Jerry

Yep. You are only into this for a delicious chicken sandwich, large fries, and a large Diet Pepsi.
I still say I came out ahead way ahead on that horse trade. I literally "ate your lunch."

LOL! If you've got another head handy, there's a second course waiting. There's a really good BBQ place a few miles south!
Jerry

There's a gutton born every day.

Locking this thread! Story has gone full circle.