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blackhat · Posted: Mon May 05, 2008 12:45 pm Post subject: 78 Head and piston rings

Hey all!

I've got a couple of odd ball questions for ya.

The first, I just bought a used '77 head w/ valves and springs (I'm not sure if it has the cam followers or not). I'm planning on sending that out to the machine shop to be gone over. When it's done, I'll just swap the head out with the one on mine. Well, that's the plan. What I'm curious about is, are the '77 and '78 heads interchangable? I checked the part numbers in the dc Auto catalog and they were the same for that year series I belive. If not, I'll have a head up for sale or trade right away. If they are, yay for me and I'll have a head up for sale/trade in the near future.

Second question.... Since I'll have the head pulled off in the near future and have access to the pistons.... bear with me, this is wear my crazy idea comes in.... can I pull the oil pan off, loosen the bolts for the rods and push the piston up and out to swap out the piston rings? I should be able to replace the rod bearings because they seem readily accessable but there's no point in doing a complete rebuild of the lower end considering its near to impossible to get main bearings. Does this seem feasable and sane? My goal is to not have to pull the engine out seeing as I don't have a cherry picker or engine stand yet.

EDIT
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Also, is $25 + $25 for shipping ($50 total) a bad price for a head?
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My First Porsche
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1978 Porsche 924 N/A

Slam · Posted: Tue May 06, 2008 3:28 am Post subject:

AFAIK, the heads are the same. I'd think $50 was a fair price for a head and shipping.

I'd also say good call on doing the rings when the head's off. It's not a crazy idea at all - but many here would advocate pulling the motor so the block can be sent out before new ring are put in. Much depends on the state of the bores. Regardless of the ring issue, doing the rod bearings may not be a bad idea. How many miles on the motor?
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'84 944 - kid blew motor
'83 944 - resting comfortably. For 12 years
'87 944 - sideswiped by trucker
'80 924 - gone
'78 924 - gone
'77 924 - rusting comfortably

blackhat · Posted: Tue May 06, 2008 5:18 am Post subject:

924RACR · Posted: Tue May 06, 2008 5:37 am Post subject:

Do the rod bearings as well as the rings - they see worse wear than the mains.

Expect the valve guides to be done-for.

Make sure to get the valves lapped in, or do it yourself. For that matter, consider pricing out a performance valve job.

Also, measure the valves. Depending on if it's an early or late 77 head, the intake valves may be small compared to yours - cost power. Likewise the cam may be different. Interchangeable, yes; the same, not necessarily.
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

gohim · Joined: 02 Nov 2002 Posts: 4459 Location: Rialto, CA

All 924 cylinder heads are not created equal.

A head from a 77 US 924 could be a Euro head with big valves, or it could be a US head with small valves, or it could be a late 77 cylinder head with other sized valves.

The head casting are different from year to year after 1977/2/

Some are better than others, because they breathe slightly better.

All are interchangable in most cases. It's just that some work better than others. Some years crack between (cylinders 2 and 3) more often that other years.

blackhat · Posted: Tue May 06, 2008 2:47 pm Post subject:

Arg... Looks like I'll be picking up a gauge to measure the valves when the head gets here.

Best case scenario is it is the same head or better. Worst case, it is the pre-77.5 head and I'm SOL.
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My First Porsche
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1978 Porsche 924 N/A

924RACR · Posted: Tue May 06, 2008 10:01 pm Post subject:

Worst case it's a pre-77.5 head and you'd want to have the bigger valves installed. Though you could, if you were going to the expense, have your machine shop source BIGGER valves than the stock late ones, and use those for even better breathing...

_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

RC · Joined: 25 Mar 2007 Posts: 2637 Location: Australia

IIRC the exhausts are the same size. Inlet is 38mm on early US and 40mm on later US and Euro.

blackhat · Posted: Tue May 06, 2008 11:20 pm Post subject:

924RACR · Posted: Wed May 07, 2008 12:32 am Post subject:

I think the diff will be more than 2hp, and you need to do some research, look for the article Big Breather (was posted here a little while back) - Eurorace modded a head to put in even bigger than 40mm. Maybe 44?

They'd need to replace the seats, of course, as well as the valves themselves, and might want a little tweaking to the bowl "above" the valves to get clean flow.

Can't hurt to ask for a quote...
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

blackhat · Posted: Tue May 20, 2008 10:35 am Post subject:

Chrenan · Joined: 15 Jan 2003 Posts: 3903 Location: Canada

My big valve head from Euro Race (now European Motorworks). Valve sizes are 44mm Intake / 37mm Exhaust:

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1987 951 - M193 Version for Japan

blackhat · Posted: Fri May 23, 2008 12:32 pm Post subject:

Well, good news for me! I went out and bought a digital caliper today to measure the valves on my head and it appears that it has the 40mm valves on it. The scale actually said ~39.80 so I figured it was safe to say they're 40mm's. Yay for me!!

I'm going to ask my machine shop if he thinks he could do larger valves. If not, no biggy. I'm definately going to have him polish them and possibly a gasket match port job. Might as well I guess.

I'd love to do the Euro Race valve job but I definately don't have the $$$ for that.

Does anyone know where to buy aftermarket big valves that fit our heads?
_________________
My First Porsche
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1978 Porsche 924 N/A