Polishing the combustion chamber?

[dingo151]

Ok....I'm starting the porting job on my head....Deep breath.


How important is it to polish the combustion chamber and whats the point of doing it? Is it a perfomance add or a detonation reduction operation?

Does anyone have pictures of their port job? I have been looking on line and its pretty easy to find information about gasket matching but I'm not sure exactly what modifications to make

Thanks
Dean

[gradon]

I have some pics in the project section. Polishing the combustion chamber gets rid of the casting flash and sharp edges and prevents carbon build-up and pinging. Scribe/mark the 4" hg hole so you can see where you can take material out/unshroud the valves as well.

[SilverXJ]

http://www.jeepstrokers.com/forum/viewt ... ort+polish

[5-90]

Ok....I'm starting the porting job on my head....Deep breath.


How important is it to polish the combustion chamber and whats the point of doing it? Is it a perfomance add or a detonation reduction operation?

Does anyone have pictures of their port job? I have been looking on line and its pretty easy to find information about gasket matching but I'm not sure exactly what modifications to make

Thanks
Dean

I would probably consider it most importrant to "break" the sharp edge where the ground deck surface meets the rough sand-cast chamber surface - you don't need to remove a lot of material, just take away the sharp corner and "round it over." Sharp edges like that are heat risers.

If you've got the time or the inclination, drop a couple of old valves in the chamber (to protect the seats,) and then start working inside the chamber proper. Clean up the sand-cast surface (same reason, just not so much,) and clean up around the spark plug hole (same reason again - there's invariably a sharp edge there.) Use an old spark plug to "chase out" the threads when you're done grinding, or find a metric screw of the same thread (M14-1.5, I think.)

It's not terribly important that you have a "mirror finish" on the chamber surface itself, but it /is/ important that you break all sharp edges and it helps to get things cleaned up in there.

Try to not change the shape of anything overmuch without having access to a flowbench - it's quite easy to make a head flow /worse/ with only a little work. Do not change the shape of the port itself - you don't want to remove material, just clean up the cast surface.

Since it's a "dry" intake setup, you can go as smooth as you like (carburetted and TBI engines need a little turbulence to keep fuel droplets in suspension, but the MPI engine doesn't have any fuel in the air until it's just going into the cylinder. Therefore, you can smooth the surface out more and improve laminar airflow.)

[RAPTORFAN85]

X2 on everthing that Silver said. Here are some pics from mine...

[Alex22]

RAPTORFAN85, did you replace all the seats on your cylinder head?

[SilverXJ]

RAPTORFAN85, did you replace all the seats on your cylinder head?

Looks like he did.. or he got a head with the seats replaced.. those don't look stock.

A few things I can add over my thread: cover anything in duct tape you don't want scratched by an errant move. I used carbide bits for most of the heavy removal. With out them I don't think the SA kit would have lasted as long (60 hours on head, some on intake, 3 hours on rods, and a bit left over). When polishing the chamber use some stock valves that you don't want. Grind then down so they just cover the valve seat. I did this by using a hand drill and a bench grinder, thanx 1bolt. They will protect your seats and give you enough room to polish. Also, even though you may be getting a valve job after wards I suggest you minimize damage to the seats. On my head the stock chamber was so close to the head gasket line I didn't feel comfortable grinding any material away. Take your time. I didn't do that much removal on mine but it took me a while.

[RAPTORFAN85]

RAPTORFAN85, did you replace all the seats on your cylinder head?

Those are the seats that came with my Alabama Cyl. Head. I was extra careful when working on the head not to touch them. As Silver said, I put duct tape on them when doing the bowl work to protect them. I also wrapped the shaft of the die grinder with tape because that's what seemed to be the closest to the seats, not the actual cutter head. When doing the Combustion Chamber work I used a couple of old valves to protect the seats for the rough work and then pulled them out to get right up to the edge of the seats. Then I put the valves back in to finish up with the cross buffs. Came out real nice.
Also as stated you will need more then what comes with the kit to do the job. I went to the local hardware store and bought a variety of different cutters and stones to do the rough work and then switched to the SA rolls and I still almost ran out of rolls! The cross buffs wear out quickly too...

All in all I was very happy with the results even tho it was like 20+ hours of work sitting on a 5gal. pail and my snots were black for a couple days.

[SilverXJ]

That reminds me, at least wear eye protection. I also wore ear plugs and a dust mask.

[nukfyrsq]

I placed an old towel over the exhaust/intake ports or combustion chamber, depending on which side I was working on, with a small shop vac hose under the towel pulling the dust away from the side I was working.

[BADASYJ]

Just to let you all know Cast Iron dust is VERY bad for you. You should wear a mask.
You can use a fan to blow the dust away from you and you get a nice breeze too. My favorite is the vacuum though.

[amcinstaller]

how far into the ports did you guys go while doing these jobs?

[gradon]

I went all the way with mine, so there wasn't any cast finish left when I was done.

[RAPTORFAN85]

I went all the way with mine, so there wasn't any cast finish left when I was done.

X2

[amcinstaller]

so the entire port was enlarged, mani to valve? or just polished (sorry, shoulda clarified)