A Project Is Brewing...

[Jeff G 78]

The "standard" shave for a P79 is 0.080" from stock.  To do this, you will need to swap the N42 valves and add 0.080" tower shims.  I did not go that route.  Instead, I shaved 0.050" and left the valves and towers stock.  I then modified the cam gear as shown in the "How to Modify..." book using the Chevy eccentric cam gear spacers.  I also modified the chain guides to get more travel and I oversized the guide bolts from M6 to M8.  With this setup, I get about 9.4:1 CR and it makes great power with little worry about detonation.  I think you get 9.83:1 if you shave 0.080".

 

The stock head is 108mm thick, so you can check how much was previously milled by measuring with good calipers.  Be SURE the top of the head isn't warped.  If it is, the cam will be forced to bend which robs power and will break the cam.  Use a straight edge on the top of the head where the valve cover sits and check the flatness with feeler gauges.

 

[Zed Head]

If I recall, you ported the other head that went to DP.  That would probably give you more benefit than a slight bump in CR.  If the top of the head was milled the measurement may not help you much since you don't how much was cut off of the bottom.  The best way to calculate your CR is to fill a chamber with a known volume of fluid.  I think that it's easier than it seems, the fancy plate is meant for super-precise work.  Water with a little soap to remove the surface tension, fill a perfectly level chamber to the top.  Should give a good number.  Then do the math or plug it into a calculator.

 

http://www.ozdat.com/ozdatonline/enginedesign/

[rossiz]

thanks for all the great input - i'm going to measure the chambers and try to do the cam adjustment method that jeff did. 

 

got busy over the weekend tearing into the lump and got it down to the short block. amazing pile of crap that came off it (power steering, a/c, efi manifold) and it looks so nice and simple once all that is removed. looking forward to seeing it all cleaned up with nuthin but a pair of su's on it

 

the po had a re-built head put on and drove it about 5 miles before pulling it in disgust to swap for a v8. he was pissed about it running pig-rich and couldn't adjust the efi (i'm guessing a temp sensor was bad) so i got lucky on this one. in addition to the new head, he also replaced the timing chain/sprockets/chain tensioners so those are some more nice re-usable parts. really the best part of all is that the head and manifolds were both recently removed, so no frozen/rusted fasteners!! what a joy - it all came apart w/no drama in a couple of hours.

 

 

look at all that crap...

 

 

one thing i did notice was that the pistons had numbers stamped in them that were different from each other - any idea what this is about?

 

[Jeff G 78]

Feel free to PM me and we can discuss the specifics of the engine mods I did.

 

I'll have to looks at my pics and see how the pistons were marked.  Those numbers *might* be fit.  I know that the rods are numbered 1 through 6, but I can't remember if the piston numbers were cylinder numbers.

[siteunseen]

Seems like I read those piston numbers were weight related.  The 3s weighed so much then the 4s & 5s, etc.  A way the factory could balance the motor a little better.  Mine have P79 stamped in the middle too.  It was a ZX motor also.  

 

RossiZ did you come across anything that was about to come loose or break?  I've torn down 3 over the last few years and always found something that got the "holy $^!#" comment.  That's what happened this weekend taking the cam towers off a head, they were really loose.  That's the reason I'm rebuilding a perfectly good running 43 year old motor.  I don't want to break down on the way to Memphis for ZCON.

 

Did that transmission have the extra bolts at the bottom going to the F54 block?  Sorta like a bracket looking thing.

[rossiz]

@ jeff - thanks, i'll definitely be contacting you about your setup, sounds like a great compromise on amount of work to do with some decent performance gains.

 

@ siteunseen - the piston weight/balancing sounds like a plausible explanation, there were 3 marked "34" (1, 2 & 5) and 3 marked "45 (3, 4 & 6). i didn't see anything about to fall apart, but the PO that had the p79 re-built hadn't torqued the head bolts, as they were all over the place on removal and he re-used the old ones, some of which were pretty corroded. when i pulled the freeze plugs i found a decent amount of crap and... an old q-tip behind the #6 drivers side plug ??!? inside the bottom end was pretty clean - a bit of crud in the oil pan, a few bits of metal but nothing that really scared me. the oil pickup screen was quite clean. there were a few odd bolts used here and there which i will replace and repair threads, but no biggie.

 

yes, the tranny had the extra "horns" on the bottom to connect the bell housing to the bottom of the f54 block.

[Zed Head]

Apparently those "horns" are for Noise-Vibration-Harshness (NVH) damping.  If you have a ZX transmission you can use them.  If you have an early transmission there's no holes for them.

[rossiz]

the trans came bolted up, so i'm just gonna re-use the horns. only downside i could see to them is they make pulling the trans to do a clutch replace a little bit more fiddly, but no biggie.

if they actually do something (NVH) then that's a plus...

[Patcon]

I didn't see the pile of parts for looking at the yellow bike. Like that!

Charles

[rossiz]

thanks for the compliment - the bike with 42 on the tail is a customized ducati that i built about 6 yrs ago. keeps me sane in between car stuff...

that build was mostly bolt-up, and i was craving a little more challenge so i built this one (43) as a full custom. frame, bodywork, etc. and pulled all the electronics from a modern ducati 2-valve engine and returned it to carbs. as you can see, a trend is emerging...

 

 

43 build pic

 

43 finished

 

[HuD 91gt]

Gorgeous looking bikes!  I should have stopped by on my way through Seattle two days ago picking up my new engine!

[Zed Head]

You picked up a new L6 engine in Seattle?