1500 - head skim - specs?

[tosoutherncars]

Hi all,

Blew the head gasket yesterday - failed between 3 & 4.

The bottom end looks fine - no wear ridge at the top of the bores, pistons are fairly clean, thrust washers done recently, etc.

I thought I'd have the head skimmed while it's off, both to ensure it's flat, and to bump the compression a little (dished NA pistons, of course.)

Anyone know how much can be safely taken off a stock head, without either a) requiring custom pushrods, or b) having the valves hit the pistons?

TIA,
Duncan

 

[blkcorvair]

if it hasnt been skimmed before you should be fine with .10

I am at .12 with flattop pistons and I had to just chamfer the rocker arms a bit to recess the adjusting ball about.010 on 3 valvea. So .10 should be good.

 

[texas_bugeye]

If your running pump gas be careful not to take to much.
heres s a little info on heads that can help.

https://www.geocities.com/MotorCity/5353/cylhead.htm

With the octane we get here 9.8 to 1 is about the limit.
On my 12G295 going on maybe in 2-3weeks Milling the head by 0.052" ( 1.3 mm ) will remove 3.8 cc of volume.
I'm sure the WOW factor and throw me back in the seat performace gain will be amazing on my BIG bore 971 cc.
pavement chewing monseter BE. okay maybe a little more.

 

[blkcorvair]

Hers an other good reading source
https://www.eighmy.com/spitfire/

 

[tosoutherncars]

I think the stock 1500 is something like 7.5:1 in stock form, so I'm not worried about going too far as far as compression is concerned... but eventually I'll run out of room with the adjusters, and need to either a) shim the rocker towers, or b) get custom-length pushrods, either of which I'd rather avoid.

I suppose the other option would be measuring the bores and seeing if I can get away with stabbing in new stock-size flat top pistons... but that really goes beyond what I want to do during 'driving season'. I'd rather get it back on the road, and build a higher-powered engine over the winter...

Maybe I'll forget the skim, and just get the darned thing back together with a new head gasket, cleaned-up head, and the viton valve seals I have sitting around.

 

[texas_bugeye]

I agree as long as you are stabing the push rod in the center of the rocker heel it should be fine you would need to take a lot of meat of the head to screwup the angles.
If you do need to make an agustment I'd change the rocker heights not the push rods. APT Ped height pads I'm sure there are others sources also. Just make sure the oil holes line up if you go that route

 

[tosoutherncars]

Chris,

You mean APT makes pedestal shims?! That'd be great...

 

[blkcorvair]

Yes there are pedalstal shims but you'd really have to take quite a bit off to need em. Taking .10 to .115 off the head should be fine and get you somewher in the neighbor hood of 9:1. Still within street gas range. More than that you'd be risking the need of shims.

 

[tosoutherncars]

Yes there are pedalstal shims but you'd really have to take quite a bit off to need em. Taking .10 to .115 off the head should be fine and get you somewher in the neighbor hood of 9:1. Still within street gas range. More than that you'd be risking the need of shims.

Wow! I'm surprised that taking off 1/10" would boost the compression that much... that's great.

I'm doing a minor porting job on the intake runners, while I've got the head off... just getting rid of the casting marks and most of the roughness (leaving it rough enough to cause a little turbulence.) I'm focussing on shortening and opening up the short side, to improve flow... I'll see if the pictures I took came out OK.

 

[tosoutherncars]

Well, the board froze and the long post I wrote disappeared into the void... :S But in short, I'm doing a minor port of the intake runners, to smooth the short side, get rid of casting marks etc.

You can see the ridge on the upper intake, about 1/2" in... looks to me like it's where the machined hole meets the casting hole.

And, halfway done smoothing the same ridge...

The bowls actually look pretty good, just a bit of smoothing here...

I suppose whether I polish the exhausts will depend on how soon the head gasket set gets here! :wink: