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Questions-12G295 head.

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jlaird

jlaird

Great Pumpkin
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Yes, I just bought a 12G295 head. Boy am I one lucky guy to find that.

Ok experts, what do I tell the machine shop guy when I get to that point to maximise its potential on Miss Agatah. She is a 997cc, that's a .060 overbore with dished pistons.

Well not really maximise but like how much off the head to keep the compression about the same.

I know about new valve guides and rounding the tops of them, and I think I know about cutting a bit off the valves to make em three sided sort of.

In fact folks any info would be appreciated, can not do this right away but would like to build a plan.

Maybe I should be asking who rebuilds em properly and what kind of a price is involved. A PM would work Hap.

Anyway Miss Agatha keeps asking and I don't know what to tell her.
 
Ok, I'll try Jack, but the condition of the core head determens everyhting, it is complete right, has valve springs , keepers all in place? If so here's a run down.

Disassemble
Degrease
Bead blast
Solvent clean
Clean all other head parts
Pressure check
Install hardened exhaust valve seats for unleaded gas
Install new guides, might as well go for bronze guides
Replace any valves that don't look good
Weigh all the springs, replace if needed
Deck head mating surfaces
Mask and paint
Three angle valve job
Install new valve seals
reassemble

I get $250.00 for the labor on this job, parts and seats are extra, so at the absolute high end, say $500 if all parts were replaced, This is higher than your average machine shop would do it for, but it's a complete restoration not just a quick valve job, it will be and look brand new when you get it back, not just glazed over. There are all kind of goodies that folks go for that will increase the price like perfofmance springs, alloy retainers, stainless steel valves, port and poilsh, etc., etc.. but sounds like you're looking for a more a good stock solid rebuild.
 
Ohh, cut and paste that answer. Yep, has valves, springs, etc. in place.

Now, three angle valve job? Would that be the bit in Vizard page 163?

Another item please. I read and hear a lot about decking the head to insure that the size of the combustion chamber stays the same (ie, the compresion). Is this figured for every engine seperately or with known bits is it a given. Miss Agatha is .060 over with low compression pistons (dish shaped) stock replacements from Moss.

How about bullet shaped valve guides as long as they are being replaced or is this just the way it is done today?
 
Call me at the shop today Jack, I talk better than I type /bcforum/images/%%GRAEMLIN_URL%%/smile.gif
 
Roger that Hap.

Hay I figured out what to tell the shop guy.

"Hi Hap, here is the head I need worked"
 
jlaird said:
"Hi Hap, here is the head I need worked"
Click to expand...

That was going to be my advice, Jack. That's what I did, at least. /bcforum/images/%%GRAEMLIN_URL%%/smile.gif
 
jlaird said:
Roger that Hap.

Hay I figured out what to tell the shop guy.

"Hi Hap, here is the head I need worked"
Click to expand...

Good call - BTW saw in Classic MotorSports that Hap is going to be speaking in Florida in January at the British Motor Trade Association in St Pete's

Congrats Hap!
 
Jack

If you cam it, there will be a problem with the block deck and pocketing will be necessary.

I am sure that you have heard this and more from Hap.

Please let me know what you decide to do, I have a similar project coming up.

Pat

Ahheemm, sorry Jack I misread as a 12G940,

Instead, deck, deck your head,

Pat
 
Jack, this is one of my 12G202 heads, virtually a clone of the 295, but with only 26.1 CC chambers (as stock), and slightly smaller intake valves. I think these chambers are about 18 CC, but I'll have to measure them again, as I lost the spec sheet.
This head measures 2.598" thick vs the stock 2.750".
Jeff
 

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Boy did someone polish out those chambers. Preaty.
 
Jack, I had MiniSport in the UK do this one for me. The reason I went with the 1.16" intake valves is that is it's the biggest I can legally go under the rules for a 948 in H Production. I can't run a 295 head on a 948 and get away with it.
Jeff
 
Ho, on the street anything goes. And in this case even looks stock.
 
My 12G295 head comes off my 10CC engine today as I begin the teardown.....so, somebody tell me how to put a little "omph" into it...
 
Tony, Jack's advice is wise here

jlaird said:
"Hi Hap, here is the head I need worked"
Click to expand...

/bcforum/images/%%GRAEMLIN_URL%%/grin.gif /bcforum/images/%%GRAEMLIN_URL%%/grin.gif /bcforum/images/%%GRAEMLIN_URL%%/grin.gif

Engines are one of the areas where my tool is a VISA card. YMMV.
 
Chap 9 Vizard. Going fast takes money, so how fast you want to go? Hehe

For starters special valves are $45 per. Shaveing the head increases compression. Porting and releaving improves power. Pollishing combustion chambers improves power.

That all said, let an expert do it after you read Vizard and see what all is involved.
 
I'll read Vizard tonight.
 
I'm one of those kind of guys that is too cheap, and too good at mechanical work, to have someone else do it. (That's why I became a mechanic to begin with.)

For me, no special rimflow valves. Cost too much and not enough extra street performance, especially with gas prices as high as they are. Good flow is a combination of a lot of things. Rimflow just helps a bit. Also, ask anybody, Stainless valves just aren't for the street! And I prefer iron guides.

Vizard's book is just what they say, The Bible of A-Series Engines. Porting can be done, well even, by following Vizard's guidelines. But don't expect a racing head. Most important is the alignment between manifold and head and cleaning up around the valve seat and guide. Also streamlining the guide and valves. If done properly, you will have a head 1/2 to 3/4 as good as a good professional would make. If you have any friends with a flow bench, you can do better, though it will take lots of time. (I fortunately have the local university (DTU) with their own DIY workshop. They have LOTS of equipment.)

Compression should be determined first. Chamber size can then be computed (take into consideration head gasket thickness and ring land free volume.) Measure the chambers as described above and then determine how much to machine off. Though it's hard to put metal back on, compression can be lowered again by using a thicker gasket.

And Jeff, That picture doesn't look like a 295 "open chamber head".
This picture does. Yours looks like a closed chamber head. Is the 202 a closed chamber?
med_gallery_128_44_431455.jpg
 
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