Coolant System Pressurized When Cold

That didn't even cross my mind, but it definitely makes sense. I'll talk to the builder about it. Thanks!

 

Where did you end up taking it?
Chris

 

Gellner Engineering in Parma, OH.

 

They did the machine work on mine 20 some years ago.

 

Well, I got all my parts back from my engine builder. It turns out the engine decks were not flat and that was likely the cause of the combustion gas getting into the coolant system. He had to take 0.008" of the decks to correct the issue. The heads were pretty good, so he just skimmed them to true them up.

I should be starting the engine build soon. I'm sure I'll have plenty of questions, since this is my first build.

 

.008?

What is your quench distance now?

I'd have expected that they'd cut WAY more than that to get the quench right. Once the block is set up in the milling machine, it's no big deal to cut enough to get the pistons somewhere near the deck surface.

 

This is my first rodeo, so take this with a grain of salt.

I measured the piston-to-deck distance as 0.005" in the hole when I tore down the engine. So, now the pistons should be 0.003" out of the hole. I'm going to double check this once I have the pistons installed.

My compression was 10.6 with a 0.041" head gasket. I need to cc my heads again and recalculate my compression, but preliminarily I'm thinking of going with a 0.050" head gasket to keep the compression about the same and to not increase my quench too much.

 

Very good. I was expecting that the pistons were WAY down in the hole.

One wonders if you can carve some metal out of the chambers--some additional unshrouding of the valves, or deepening the valve reliefs in the pistons, perhaps--to retain a similar compression ratio, and still use a ~.040 head gasket.

 

Buick nail head chambers do like some unshrouding work over by the plug side of the chamber and starting where the valve sits in reference to the chamber a 300" lift up to .600" .

 

So I did some research, because I wasn't sure what unshrouding meant. I have a general understanding now.

Below is a picture of one of my combustion chambers. To me it looks like there has already been some work in the chambers, which included unshrouding. Does it look like that to you guys?



Is there an opportunity to take out 2 cc's of material? That's what it would take to get back to my original compression of 10.6 with an 0.041" head gasket.

If the piston reliefs were deepened, then the rotating assembly would have to be rebalanced, correct?

The way the engine is now:

• 0.041" Felpro gasket = 10.78 and 0.038" quench
• 0.045" steel gasket = 10.68 and 0.042" quench
• 0.051" steel gasket = 10.54 and 0.048" quench

Perhaps I could run a little more cam and go with a 0.038" quench??? (I'd obviously need to check the DCR, street manners, etc.) I guess that's a general question for now. I plan to start a new thread to discuss my cam options, so it's easily searchable by other members who are researching cams.

 

Kinda appears that some work was done around the exhaust valve, and smoothing the rough casting. Look at how the Stage 1 heads are unshrouded around the intake valves. I'm sure someone has a photo of those chambers.

Playing with the valve reliefs in the pistons would not change the balance much at all...but would be somewhat difficult for most folks, and you'd want to verify that the piston head has enough material so that deepening the valve reliefs doesn't weaken the piston.

 

Here are the "usual" pics we pass around of the factory 455 Stage 1 combustion chambers vs standard production. Buick used cutters that piloted off the valve guides in a secondary operation to make room in the standard heads for the bigger Stage 1 valves, removing material from the chambers as well as enlarging valve seats & further in. The castings were the same, only the machining was different.



I went a bit further with my original 430 heads when I converted them to Stage 1 valve specs. Lots of room to make more room in the chamber if you want to, no need to bother with the pistons. If you want to gain a cc or two, just get rid of the "bump" near the spark plug as I did. It was there only as a place for fixturing during machining operations, serves no other purpose.



Devon

 

Interesting. I was wondering if I could remove the bump. I didn’t know if it had a purpose, like causing the charge to flow a certain way for optimal placement when the plug fired. Thanks for posting the pictures.