Will this head work??? Please Help

[dillenger1]

why peen only around the "front of the prechamber?why not all the way round?

[zukgod1]

why peen only around the "front of the prechamber?why not all the way round?

Because the gasket seals around the back part. The area peened in this pic is open to the combustion chamber, doesn't touch anything.

[arb]

You had your head shaved but you didn't do a valve job ? (Regrinding the valve seats and valve faces - a 3 angle being better than single angle)  I would take the time to do this too. If you pull the valves and the seats and faces look very good, maybe just "lap" the valves - that is polish them with lapping compound to give the best seals possible.

Your compression ratio will absolutely change if you change the chamber in the head. It is a common misconception that it will not by shaving the head alone. Doing a valve job w/o shaving the head, or changing the thickness of the head gasket will also change the ratio.

How much ? That all depends on how much you changed any given part. Maybe you went from 23.11:1 to 23.37:1 ;-)  Maybe much more. Compression ratio by definition is the ratio of total volume in the cylinder (valves closed) including prechamber / squash area, etc - at bottom dead center VS. the same at top dead center. Here is a good calculator that takes into account all the variable.

http://www.csgnetwork.com/compcalc.html

When you "blue print" an engine for aviation / racing, many builders will actually measure the CC of fluid the chambers hold (as well as intake / exhaust runners) on each cylinder to be sure each has the same compression ration and therefore the same theoretical HP.

[arb]

WOW !! I was just playing with the numbers in the calulator - I moved the example's combustion chamber to 45 cc to get the CR in our range - 22.7:1 - then I added 1 mm of head gasket thickness ( .039") and the compression dropped to 18.4:1 !!!

So, changing the gasket / shaving the head has a real effect, depending on how much you change things.

[zukgod1]

WOW !! I was just playing with the numbers in the calulator - I moved the example's combustion chamber to 45 cc to get the CR in our range - 22.7:1 - then I added 1 mm of head gasket thickness ( .039") and the compression dropped to 18.4:1 !!!

So, changing the gasket / shaving the head has a real effect, depending on how much you change things.

This misinformation needs to stop!

Shaving the head on these engines DOES NOT change the CR.

The entire combustion area is in the gasket and pre cup.


Please PLEASE stop post up mis information...

[arb]

WOW !! I was just playing with the numbers in the calulator - I moved the example's combustion chamber to 45 cc to get the CR in our range - 22.7:1 - then I added 1 mm of head gasket thickness ( .039") and the compression dropped to 18.4:1 !!!

So, changing the gasket / shaving the head has a real effect, depending on how much you change things.

This misinformation needs to stop!

Shaving the head on these engines DOES NOT change the CR.

The entire combustion area is in the gasket and pre cup.


Please PLEASE stop post up mis information...

This would imply there is absolutely zero space between the valves, head, prechamber and the piston.  If there is space, it is part of the compression ratio calulation, even if it is 1 mm or 1 micron.

I am sorry you feel it is mis-information. Can you point someone to engineering data that would show there is 100% contact between the piston and everything on the head ? Or that this is mis-information ? As the calulator can show you, the amount it changes depends on how much change there is.

http://www.answers.com/topic/compression-ratio

[zukgod1]

That post wasn't directed exactly towards you even though I quoted you, it was more of a point to be made regarding this issue. That being said.



The amount of space between the piston and valves is so minuscule there is no reason to figure it in.

What I'm getting at is we seem to be telling people that milling the head changes the CR and in reality it does but not enough by any standards to be discussing it or to be bringing up the physics behind it or thinking it will change the way the car runs and this is what you are portraying.

Your comments are misleading people in regards to these engine.
You reasoning may be accurate but in this matter your going way overboard.

These are not gas engine that get the CR drastically altered when the head is milled, the CR is figured by the HG and the Precup.

If you want to start a thread discussing CR please do so I'm sure it will be interesting.

[blkboostedtruck]

Yes Andrew is absolutely correct !
arb i think your getting confused between gasser and diesel C.R. your formula will work on gassers but does not work the same with diesels !
there was a paper floating around about it! i don't have it anymore! it's on my other lab top that don't work! maybe somebody might still have it and re-post it
Duane

[arb]

You are absolutely correct - the formula for that site is not correct for our diesel - the concept is. The squash area under the valves is certainly made smaller by milling.

Look at the area of the squash area - its what ? About 25% - 30% of the bore ? That means in the example I gave for 1 mm milling would be only 25% - 30 % of the change in compression the formula gave - so instead of going from 22.7:1 -  to 18.4:1, it would be more like 21.6:1 - still a reduction, but I can see your point it is not huge as it would be on an open chamber as in a gas engine.

[Smokey Eddy]

The difference due to the shaving would be SO negligible it's ludacris. Just so long as the vaves dont hit the pistons? triple check the timing?
I've been a tooth out before by accident and thankfully they didn't mash.

[autoholic]

So what is the accepted limit in shaving these heads? I know some say none, but many of us have with no problems. I agree that it's a must to grind the seats/valves to negate the head shave (a new valve job is worthwhile anyway), isn't there only like 10 thou piston to valve clearance stock? going closer seems scarey, and provides even less margin of safety in the event timing is off.