212cc predetor

[paz1969]

I am doing a few modifications replaci replacing stock cam with 265 lift, billet connecting rod same length as stock : molly push rods. Valve train upgrades are 26mm intake 24mm exhaust.,1.3/1 rockers, 18lb springs,.060 shims for springs.my friend is polishing and porting the head.how much should i deck the head?30,000 or 40,000?i am using a copper head gasket. .016 thick. Also should i take some off of the block.some one said to run only 18lb springs. 26 lb springs would be to much.so im confused wether to run 18 or 26 lb springs.im running a 22mm mikuni w manifold.any advice is appreciated

 

[paz1969]

Anyone?

 

[zbuck]

As far the valve springs, what does the cam manufacture recomend? As far as shaving the head, use the old play dough trick.

 

[jamyers]

...how much should i deck the head?30,000 or 40,000? i am using a copper head gasket. .016 thick. Also should i take some off of the block.
...

Whew! Ya know, they invented capital letters and paragraphs for a reason... Also, hard to take 30,000 or even 10,000 off of a head that's no more than 6 inches tall - you're still 9,994 inches short. Okay, I'm just being picky and harassing you, I'll stop now.

I've milled heads and decked blocks, but not on these small engines. I can say that you're asking a BIG question, and the answer is:

"It Depends":
How far 'down in the hole' are the pistons now?
What rpm are you going to run?
What static compression ratio do you want?
Is the cam going to be installed X degrees, advanced, straight-up, or retarded?
What dynamic compression ratio do you want?
What quench height (closest distance between piston top and head) do you want?
What connecting rod are you running (need to know how much it stretches at high rpm, quality rods will stretch less)
What piston - dished, domed, flat-top, valve-reliefs?
What minimum valve-to-piston clearance do you want/need?

I'll say that in the V8 world, most guys with combustion chambers similar to a clone engine (a mostly "open" chamber in the head with a slightly dished piston) shoot for something like .035" or .045" quench height via zero-decking the block (piston tops come right up to the deck) and using the head gasket to set quench height. If you're going to use a .010" head gasket, you'd want the piston .025 or so down in the hole - your machinist would then cut the block to whatever dimension that it.

I would suggest 3 things;
1. Head over to a racing kart forum like http://karting.4cycle.com and do some reading on specific engine building / machining practices and dimensions, and
2. Play around with an online "Dynamic Compression Ratio Calculator" and get some ideas on how different setups would work.
3. Find a GOOD machinist who has worked on these engines before, he'll be worth his weight in gold.

 

[paz1969]

Thank you for the information much appreciated. as for my spelling and English I finished a fifth grade and off to work i went.i apologize

 

[zbuck]

Jamyers, very good explanation. Another thought, not knowing what a stock head gasket thickness is, you might not need to deck the head when using a .016 gasket.