Cylinder head swap

[Ctopher87]

I was curious if a could swap a 78 or 79 head onto my 80 sg. If I understand correctly the heads from the earlier years are slightly different. I know the timing curve for the earlier cams is not the same. Really what I'm trying to figure out is could I swap my cams into the head from a 78/79 and run? Any modifications that may be needed to the head itself? I noticed today that I have a small crack near cylinder 3 on the exhaust side. Right were the stud to mount the exhaust is. I've found a couple of heads close by that are affordable however both are from a 78e.

[BA80]

Check you clearances. The early head has a smaller combustion chamber and the later pistons have a higher dome. The early heads also have a smaller intake valve. It might not run too well with the milder cam in the 80.

[TopCatGr58]

Hey Ctopher,

Like Greg said, the later heads use larger valves, and so that's partly why the the cams don't have as much lift, because they can allow equal amounts of flow since the larger valves don't have to open as much. So...trying to run those 80 cams with the earlier heads/valves probably would not open the valves as much and so you would have less space and time to allow proper intake volumes of the F/A mixture.

The earlier heads/valves have more lift so the valves are pushed out further from the head closer to the higher domed pistons although they do have wider valve reliefs, and so that's why there's concern about the valve/piston clearances.

Does the crack seem to go thru to the exhaust port, valve guide area, or combustion chamber??? Have you looked into finding someone that welds aluminum to see if they think it could be repaired???

T.C.

[BA80]

I think the problem will not be so much lift as duration, the early cams had a much longer duration. The valve stayed open longer allowing more flow.

Hence a different ignition timing curve.

[Ctopher87]

I knew there was a diffrence. Right now the crack is small enough not to cause any problems but it could spread in either direction. I could have it welded up if needed. I appreciate the feedback. Now as far as swapping I think that's ruled out at least for the earlier head.

[3Phase]

Ctopher87,

A few years ago I used clay to check the valve clearances with the new-style 3H5 pistons and the old-style 2H7 cylinder head. I found and reposted some of the pictures for the thread.

The valve and piston clearances are okay when the cam-to-valve shim clearances are set near to maximum but a little close when they're at minimum:-


Valve to piston clearance: 2H7 head with 3H5 piston | Max cam-to-shim clearance

[3Phase]

Argh! Repost after Photobucket crash

Ctopher87,

A few years ago I used clay to check the valve clearances with the new-style 3H5 pistons and the old-style 2H7 cylinder head. I found and reposted some of the pictures for the thread.

The valve and piston clearances are okay when the cam-to-valve shim clearances are set near to maximum but a little close when they're at minimum:-


Valve to piston clearance: 2H7 head with 3H5 piston | Max cam-to-shim clearance

[BA80]

I remembered this Scott but couldn't find it. Was this done with the early cams or later?

[3Phase]

It's the early cams and head with late-model pistons. The clearances in the picture included using a new but torqued aftermarket cylinder base gasket too, not just sealer.

TL;DR version: It will work but stay on top of the valve clearances and don't misshift.

[Ctopher87]

Well I took the plunge and ordered a head from ebay. The milage is unknown. Also found vesrah valves on ebay uk for about 20 bucks each so I think I'll rework the "new" head with new guides springs and valves then swap heads. While I'm in there I'll replace the timing chain also. My engine has close to 50k miles. Is there anything else I should replace while I have the head off?

[motoman]

Actually, no need for a new cam chain with that low a mileage on it. Instead, I would replace the stock cam chain tensioner with an automatic cam chain tensioner(ACCT). Some 60 options out there for an ACCT. My preference is the ACCT off the early Yamaha Venture 1200. They use two of them on that V-4, and either one is fine as they are both the same.

[Ctopher87]

I was interested in either this or a manual tensioner. It seems like I'm getting some chain noise every 5 or 600 miles and have to remember adjust the tension

[skids]

I would replace the cam chain also if I were into this kind of surgery. As I understand it, there are two types of cam chain (heavy duty vs. regular?). I replaced a cam chain once because my tensioner was almost out of travel, but after the cam chain replacement, I was disappointed with significant tensioner capacity.

[Ctopher87]

Sounds like a plan. I already have a new chain on hand from ek chains. When I was in there around November checking valve clearache I looked at the gears on the cams and didn't notice ant wear. It's gonna be some fun. I've never worked on an engine with the cam chain in the middle.