11 replies to this topic

[Leekr89]

ok so i may of got carried away with the dremel but im just hoping i havent damaged the cylinder head too bad... :S i was grinding away following the yellow bible and didnt realise how much metal i was taking away, i have taken the lip off between the 2 valves but have starting taking away small parts of the valve seats, i wouldnt normally be so bothered but i think its a new old stock head (11 stud also but unsure why) i have only touched one combustion chamber and hopefully it is fixable (not by me obviously!) heres some pics to show the damage:

[Carlos W]

I wonder whether having bigger valves professionally fitted would fix the problem????

Please note my uncertainty though.....

[Deathrow]

Surely they should still seal. You've not affected too much of the face mating face.

Worst case I'm sure you could have the seats recut or unleaded inserts fitted.

[tommc92]

maybe have the valve seats re-cut?

[Bungle]

lap the valves back in with a bit of paste then stick some fuel in the chambers and check for leaks

[maggies_minder]

ive got 2 spare never used 12G940 metro heads, i was going to "vizard-ize" as im reading the section on heads now.
but im too scared... they look more Eddy Izzard than David Vizard if i have a go.

[GuamMini]

Thats an easy fix, I used to do this with a drill no Dremel yet at that time.........

[dklawson]

You were going to need to lap the valves anyway so start with that as Bungle suggested. If you don't get a nice, uniform, matte appearance all the way around, have the valve seats re-cut. The damage you have is not too bad.

If you are scared using a Dremel and lost track of how much material was coming off, be very, very careful if you ever use an air powered die grinder. They are much more suited to the task but they are much more aggressive.

You said you "think" this is a New-Old-Stock head. Why do you think that? If it is, you probably need to take the head and valves to a machine shop anyway so they can ream the guides to size, cut the valve seats, grind the valves, and lap them in.

[Cooperman]

You would be best off removing the valve guides, grinding away most of the valve guide bosses where they intrude into the inlet & exhaust throats.
Then complete the cutting and smoothing of the chambers using, as DILLIGAF rightly says, some old valves to shield the seat.
Press in some new guides to the correct position, take the head to a machine shop and have them lightly 'kiss' the valve seats with a valve seat cutter.
Then just lap the new valves in as normal and 'jobsagoodun'.
The work done on the chamber you started on looks good. Make them all the same +/-0.5cc and it'll be good.
Remember that you will need to have the head skimmed to get the compression ratio correct which means after fitting and lapping-in the valves you will need to fit a set of plugs. Measure the chamber volume, do the necessary calculations and have the correct amount as measured skimmed off the head, which means the head has to be stripped again. (.I did a lost about how to do C.R. calculations just recently which might help you with this)

[Cooperman]

You would be best off removing the valve guides

Don't bother removing the guides, just grind 'em away and remove what's left after you've finished..... wayward dremel's can damage the guide boss/hole.

Yes, you can do this, but it makes for even more grinding especially if you don't have a die-grinder. It's even worse if the guides are phosphor-bronze or manganese-bronze as that material clogs the grinding stones. I always remove the guides first and have never had any issues with grinding across the guide holes.

[Artful Dodger]

best way to modify a combustion chamber i found is to keep some OLD valves in as blanks held in by a rocker spacer spring with the collects ect. so then you cannot touch the valve seat and make the chamber flush to the valve, then get the head sent off to get re-cut if you want to put bigger valves in. just a more safe way of head cutting. you will not be able to use the valves afterwards though.

Edited by MiniclubmanGT, 18 November 2011 - 11:03 PM.

[Cooperman]

best way to modify a combustion chamber i found is to keep some OLD valves in as blanks held in by a rocker spacer spring with the collects ect. so then you cannot touch the valve seat and make the chamber flush to the valve, then get the head sent off to get re-cut if you want to put bigger valves in. just a more safe way of head cutting. you will not be able to use the valves afterwards though.

Actually if you are having bigger valves it is best to get the throats bored to the minor diameter of the valve head about 1/4" deep, but no seat cut at this time. Then grind out to the profiles you want, then fit the guides and get the new larger diameter seats cut.
If valves are staying the same size using old valves to shield the seats is an excellent thing to do. I have a big boxful of old valves just for this.