Motorsports Village

Combustion Chamber
Page 1 of 1

Author:  Clinker [ Thu Dec 31, 2009 2:12 am ]
Post subject:  Combustion Chamber

Hi Guys

Merry Xmas and a Happy New year to you all, I hope this year is great for all of you.

Now the question.

The valve seats in the combustion chamber, does it matter if the seats are not flush with the casting. I have a new pair of CNC'd heads and you can see where the casting is not sufficient and there is a lip of the valve seat protruding. It isnt much but if you run your finger over the casting and the seat you can feel the sharp edge of the seat. Its probably about 10 thou.
I dont want to take some of the seat as it will start to get close to the valve contact patch, Its a drag only car and on methanol.

Thanks Trev

Author:  Mike Rogers [ Fri Jan 01, 2010 8:31 am ]
Post subject:  Re: Combustion Chamber

Trev you do not want that sharp edge it will cause a hot spot in the chamber the edge will glow.

Author:  Clinker [ Fri Jan 01, 2010 5:17 pm ]
Post subject:  Re: Combustion Chamber

Ok thanks guys, thats not good news for me hey.

This term top cut, is that the top of the actual seat contact patch with the valve or the last taper cut of the seat for the blending. Also, how much seat should there be past the contact patch, does there have to be like 50 thou or can i blend this to be really close to the seat contact patch. Secondly, if I have to blend this further than the seat angles, would it hurt to have the seat cut deeper to fix it up again.

Thanks again

Author:  Clinker [ Sat Jan 02, 2010 2:11 am ]
Post subject:  Re: Combustion Chamber

Thanks Guys

I dont think I will get away with a simple blend it in, I just blued up the seats so I could get a good idea of this top cut, I think the top cut will be gone by the time I blend it away. Here is a pic of the problems. Do you think I should take it to the local valve guys and get that top cut taken down until its perfect and then get all the others done the same amount and then have the seats re cut. I think I would be happier with that and then make those two polishing valves. Do you think I would be better of doing that, or should I just move to the states lol.

Thanks Trev


Author:  rick360 [ Sat Jan 02, 2010 11:41 pm ]
Post subject:  Re: Combustion Chamber

How many chambers/seats are like that?
Are the bad seats all exhaust?
Are they all similar to the pics in the amount of circumference that is sticking above the casting?


Author:  Clinker [ Sun Jan 03, 2010 2:22 am ]
Post subject:  Re: Combustion Chamber

Hi Rick

All the Intakes are ok, I can blend them in as per Mikes directions plus the casting is above the seat. Its the no 2 and 3 exh on both sides that is the issue with no 3 on boths sides being the worse as in the pics.

Should I sink the inlets down as well or is it ok to have the exh sitting lower than the intakes.

Thanks again for all the advice guys,


Author:  shrinker [ Sun Jan 03, 2010 3:42 am ]
Post subject:  Re: Combustion Chamber

With that issue going in with the surface of the head I would be questioning the entire shaping of the chambers. Without mentioning what brand I recently had experience with heads that the chambers were .080" different in one head to the other. The whole thing was a mess on the dyno and the heads had to be milled and recut with cnc to get the chambers the same. The burn was totally different on one bank to the other on the dyno. YUK. Its not just the CC's that matter. There is at least one reputable manufacturer in the USA that is pumping out questionable products sometimes. I would be sending the heads back or fully digitizing them and milling them and correcting the chambers to all exactly the same shape. If only some cylinders are like this then it brings into question if your having the same issue as I saw. You may as well throw Darts at a board and pick a chamber. Oops that might be the brand.

Author:  Clinker [ Sun Jan 03, 2010 4:42 am ]
Post subject:  Re: Combustion Chamber


There isnt an issue with the ports or the chamber, It is a CNC job and that part of it is actually very very good. I did CC the ports and also the chambers when I received them and they where all spot on. the actual machining and workmanship is good on all parts of the heads, its just the finished product that is lacking, probably just pulled it of the CNC machine and didnt inspect them.

Author:  shrinker [ Sun Jan 03, 2010 5:36 am ]
Post subject:  Re: Combustion Chamber

That's what I'm saying. the heads I saw measured the same CC but the shaping was different per chamber and per head. Obviously if you only have this issue with some chambers then there not all the same are they. So dont trust anything is all I'm saying.

Author:  Clinker [ Tue Jan 05, 2010 12:55 am ]
Post subject:  Re: Combustion Chamber

Hey guys

Just to let you know, the heads are getting fixed. I bumped into a guy I sorta know and was chatting about my problem, he said no worries he would take em to his work and fix em for me. I then found out he works for one of our V8 Supercar teams in engine development and they have all their own machines etc etc. He says he will redo all the seats with the cutter they use on the supercar engines. Apparently they have better seat cutters and these things dont actually have angles, they have like a round seat with just the flat part for the seat.

Anyway, thanks for all the help and advice


Author:  Buster [ Tue Jan 05, 2010 2:21 am ]
Post subject:  Re: Combustion Chamber

Hi Trev,
If those heads are what i think they are, dash 9's? i have the same heads but in cast iron and have the same issue with the seat inserts sitting slightly proud of the chambers. My chambers haven't been cnc'd though . I bought them as unfinished castings and got the seats cut in them and i too have that sharp edge at the edge of the seats in places.
A couple of questions to everyone. Sorry if they've already been answered.
Will that edge promote pre ignition as i've split a few bores over the years.
And is the fix as simple as just recutting the seats a bit lower .


Author:  Clinker [ Tue Jan 05, 2010 2:49 am ]
Post subject:  Re: Combustion Chamber

Hi Buster

They are sort of Dash 9's, but they are a blank casting with different water jackets and different valve locations, but as far as heads, yep they are dash 9's. You are spot on, pre ignition caused by that hot spot created by that sharp edge, You can do what the guys suggested to me, blend em in, but on mine, i had to blend that top cut away completely before I could get rid of the edge, then by the time I contoured the chamber I had cut have the seat away. I paid $4700 for the bare heads so for me I wasnt prepared to have a half job, so it was better to just get the seats re done then I will do as Mike said and make up some blending valves and blend away and then re CC the thing.

Its fixable but a shame we have to do it especially when the head people could have just sunk that seat a few thou deeper when they machined them up.

You anywhere near Albury Wodonga.


Page 1 of 1 All times are UTC - 5 hours
Powered by phpBB® Forum Software © phpBB Group