32 replies to this topic

[sqweaka]

that should help
mine had the bypass hose fitted

[Bill USN-1]

http://www.minifinit...5_head_to_a_998

Thanks but it's a few minutes late!

I decided to go for it and did it manually!!

I went .100 deep and left about .100 distance from the gasket surface.









This is the only water passage on the 940 head that is not the same as my 202 or 295.

Edited by Bill USN-1, 07 October 2006 - 10:44 PM.

[Retro_10s]

looking good dude!

[Bill USN-1]

OK a little more data.

First here is some specs of my head.

I measured both heads just to see what I had.
The measurements may not be exact, I was comparing them...

stock 202 head,
28cc chamber
1" exhaust valve
1.2" intake valve
2.720 thick

Jon speed 940 (don't ask me I was just buying a 940 head)
19cc chamber
114 exhaust
1.4" intake
2.730 thick




I decided to use the small bore head gasket and I am using the 1098 rockers off the 202 head.

There has been a lot of discussion on this so here is what I found.

1. The exhaust valves are moved. If you look at this pic you will note the 2 middle and the 2 outer rockers do not line up.



A closer look. Note the arrow for the direction it needs to go.



So how to fix it?

Well the outsides are easy, just remove the cotter pin at the end, then the washer spring and the rocker. Now install the spring and slide the rocker back on. Then the washer and cotter pin....done....
Now the spring will hold the rocker to the outside.




But what about the 2 middle ones...
Well pull that left cotter pin back out and slide everything off all the way to the middle.




Now what I did was use a washer for a spacer next to each mount to move the rocker in. These were about .075" thick. Then reassemble.

Now they are all lined up...

[miniboo]

i am sure i read that you should use the large bore gasket when doing this mod

[Bill USN-1]

i am sure i read that you should use the large bore gasket when doing this mod

Me too but I could not find out why!!

The bores just seemed to be too close to the water jackets for my liking.

Edited by Bill USN-1, 09 October 2006 - 08:43 PM.

[miniboo]

oh yeah you need to use a 1275 top rad hose and the bracket from a 1275 aswell!!

[Bill USN-1]

So I thought all was good till I started to tighten the rocker stands down and the push rods for the 2 center valves started to get tension on them from the side???

So I pulled everything back off and had a look...

Found the 2 center pushrod holes that run next to the center exhaust port had baked on oil built up inside them!!
This wouldn't be a problem with a completely remanufactured head that had been hot tanked!!



So I pulled out a .480" drill bit and my gun cleaning kit and cleaned them all up.
Noticed a little bit of miscasting in the holes. Some had a mismatch in the middle.

All clean!




So now that all is back together I continue on.

Here is my new bypass thermostat since I decided not to drill and tap the bottom of the head for the bypass hose.



But then I find the next difference...

They turned the mounting holes for the thermostat housing!!

So now the raditor upper mount doesn't line up!!

Well I had to improvise for now. Found some old manifold studs and remounted with just 1 bolt for now.

While it was still apart, I noticed quite a port mismatch on the exaust side of the head. Guess I have some porting to do before this head goes on a 1275!!




Well it's together and running now...just a few things to finish up. Then I will see if the bottom end will hold together?? It's just a little tired and I can hear all kinds of things loose in there!!!

[Retro_10s]

Really glad to finally see some pictures of people really doing this, usually we get to this stage and the thread dries up no pictures or posts or anything appear.

You're work looks good bill, how does it run now?.... any large noticeable differences??? how did the porting go????

[Bill USN-1]

Really glad to finally see some pictures of people really doing this, usually we get to this stage and the thread dries up no pictures or posts or anything appear.

You're work looks good bill, how does it run now?.... any large noticeable differences??? how did the porting go????

I have about 50-75 pics of the entire process but figured it would take too long to view in the forum.

I'm hoping to road test it tonight. My biggest concern is the bottom end!!!
Sure sounds like piston slap and loose cam bearings...But the cylinder walls looked pretty good and I could see the top ring end gap...so.

I put off the porting until I build my 1275. I would drop it in now but hit a few snags like....
1. it's a 96 MPI block with no distributor hole so i have to make up a EDIS system for it.
2. It looks like the tranny has different shafts. From what I can tell they were inner CV's on the later motors.
3. I have to decide on a clutch and flywheel. old or new style????

So it's more parts to find so i can go big bore!!!

[Zenob1]

Gotta agree with Retro 10s - it's nice to see pictures of someone doing this mod. I have to say I'm very interested in this myself seeing your work has given me more hope that it is do-able.

Bill,

What are you using to make the pockets? That seems to be one of the most important factors in this job.

Looks goos to be honest. Nice work.

Matt

[Bill USN-1]

Gotta agree with Retro 10s - it's nice to see pictures of someone doing this mod. I have to say I'm very interested in this myself seeing your work has given me more hope that it is do-able.

Bill,

What are you using to make the pockets? That seems to be one of the most important factors in this job.

Looks goos to be honest. Nice work.

Matt

I just used my air die grinder with the carbide bit that I show in one of the pictures.
It's a fine bit 1/4" in dia.


If I had to do it over again, I would probably take less material out.
I would drop the head on the block without valve springs and put a little white grease on the valves. Then drop the valves down to see if they touch. Then the grease will mark where.

Then you can just give a fudge factor of an extra .050 to be safe.

I think it would be a lot less material to remove!!

[Bill USN-1]

.......... how does it run now?.... any large noticeable differences???

Ok, got to pull it out of the garage tonight and give her a try....







WOW

What a difference!


She pulls much better on top end now.
I can't wait to get the GM fuel injection and a LCB on this thing.
The waxstat carb seems to be holding it back.
Might be time to hook up my Wideband O2 sensor and see where she is at?

My 7.5 disc brake setup should be arriving any day now and not too soon. Hopefully they will not need a complete rebuild since they came off a wrecked car.

Anyone got a 1275 upper radiator bracket they can send me?

[fikus01]

where are you getting you're fuel injection from and how tuneable is it??

[Bill USN-1]

where are you getting you're fuel injection from and how tuneable is it??

Ebay and very tuneable!!

It's what I do in my spare time!!

My FI forum.

Edited by Bill USN-1, 10 October 2006 - 07:28 PM.