rebuild of 68z/28 engine questions..

[black69]

I got a 20K mile z/28 from a neighbor and he had the engine rebuilt in 94 and let is sit all apart for 30 yrs. Block just needed light hone recently and new rings but kept at 30 over and they put new cam bearings in it and freeze plugs. But all the $1500 work they did to the engine back in 94 remains intact.

Heads never on. He bought in 94 a new Crane cam with the stock z/28 profile and new crane solid lifters. Both in boxes.

Reason for the post, is the second owner who had the car from 76 to the late 80s, has me scared on a few things. He said even though the assembled heads are fresh but sat, he said I should have all the shims plus spring heights checked, check the springs in a tester my engine builder friend likely has, otherwise he said I run the risk if any thing is off in a solid lifter engine, all hell breaks loose if I want to run it up to 7500.

He said I am lucky I got a non offshore cam (1994) as he said anything now is crap. When he says I may window the block by assuming things are ok, I panic.

I respect the second owner's opinions as he kept the car in great shape as a cross-ram car that the first owner had on it, and managed the realities of keeping idle above 2500rpm, and then ran it all the time between 3000-7500. he said he was always keeping the valve adjustments spot on, and had valve covers off alot. I am returning the engine to a stock setup, no cross-ram yet for me. I may not get the nitrous like rush he said the cross-ram gave at max rpm, but will be happy atleast bringing it back to life to have fun with.

Opinions appreciated (new old springs on the never mounted assembled heads ok? recheck height and spring performance? 94 vintage 'z/28'crane cam ok to use?)

[big gear head]

Checking the springs is cheap insurance. Valve springs and rod bolts are the 2 things that I consider critical. If either fails you can destroy the whole engine.

[169indy]

7500 not likely, where do you plan to do that at. If planning on Racing/Street/Drag or Track then you got a LOT of work to do. But Really how often do you plan on running it in "that reality". If it is a true Car show weekend cruzer' I would think the springs warrant checking but without cycling of compressive forces and heat and cooling the negative affects of static (Relaxed) compressed would be negligible and if they were New at that time would the available stock be considered better than todays outsourced stock.

I know of locally Nine 68/69 Z owners and NONE of them are routinely spinning their 100k show car near this. They Drive differently then they Bench Race.

7,500 Yes Maybe a VERY Very Few, Please post your Videos of your Tach on your MO/DZ motors doing this on your country roads near your house.

I am not being Negative just wondering about your usage, I would think there are a bunch of Engine related things to consider If you want to routinely spin up there.

[black69]

Originally Posted by 169indy

7500 not likely, where do you plan to do that at. If planning on Racing/Street/Drag or Track then you got a LOT of work to do. But Really how often do you plan on running it in "that reality". If it is a true Car show weekend cruzer' I would think the springs warrant checking but without cycling of compressive forces and heat and cooling the negative affects of static (Relaxed) compressed would be negligible and if they were New at that time would the available stock be considered better than todays outsourced stock.

I know of locally Nine 68/69 Z owners and NONE of them are routinely spinning their 100k show car near this. They Drive differently then they Bench Race.

7,500 Yes Maybe a VERY Very Few, Please post your Videos of your Tach on your MO/DZ motors doing this on your country roads near your house.

I am not being Negative just wondering about your usage, I would think there are a bunch of Engine related things to consider If you want to routinely spin up there.

Thanks for the input. What the first owners did with this car, I do not plan to do. BUT thought once in a rare while for me, I would like to see it get to 7500 if it was designed to do that. I am lucky to put 100 miles on my cars in 5 yrs. I got the second owner telling me that his engine builder in Joliet IL had a 8K rpm warranty on it, they would replace the engine if it blew, hearing titanium straps on the mains (no idea what that means), and ultra thin compression rings to allow high RPM. I think according to my friend putting the engine together, they must have added 4 bolt main caps vs 2 which is stock? My neighbor had to have the piston compression grooves machined to allow larger 1/16 rings (which are still thin), they were that thin in the car based on the habits of owner 2, who said he copied the piston type that was in it from owner 1 (thin rings). So I am influenced by that. I never ran a small block with the rpm potential this engine has, so I plan to keep it fun and not rail road it. But would also feel safe it was built to do what it was designed to do also regardless if I ever get it up to 7500.

This car was a Nickey chevrolet ordered car that was provided at a low price to the first owner under certain conditions. He road raced raced for Nickey in another 68 z/28 and the deal was he was to bring this car to non drag events to show goodies from Nickey on the car they practically gave to him. This was a street car. What they did to the engine I really dont know, but all I have is stories on how it rev'd to the max limit often, so this is why I thought 7500 was ok for these 302s. They obviously changed the pistons from stock ring width, second owner said that was all to get max rpm.

Definitely learning redline on these is more dangerous than I thought. Appreciate the education.

[Lynn]

Spend much time at 7500 and you will likely pull a rocker stud, unless someone converted them to screw in studs or they have been pinned.

As far as springs, shims, installed height and spring pressure, I would NEVER assemble an engine I got in parts without doing all of those things. Just basics.

If you have a vise, you can buy a cheap spring pressure tester from Speedway for $60 MOL. One of the good things about the 30 30 cam (or the Crane copy from 1994) is the soft ramps that allow use of springs that are NOT that stiff. If you find they put really stiff springs on there (like the over the counter 142 spring) you can put stock springs back on it.

I don't know why you would rev it about 6800. There is plenty of torque at the next gear shifting at 6800.

[juliosz]

I had a similar situation with my 67 Z. The original owner went through the engine sometime in the late 70s and it had never been fired. I was tempted to prime the oil pump and start it but cooler heads prevailed and I had a friend go through it. Good thing I did because I found the original main and rod bearings were re-used. Another issue was the rings were stuck in the ring lands due to old assembly lube drying out. There were some other issues as well so it was money well spent going through it.

BTW, me and my buddy thought the valve springs would be shot from sitting partially compressed all those years but each of them tested good!

https://www.yenko.net/forum/showthread.php?t=176109

[Rsconv68]

I would tear it down, inspect it, install whatever new parts are suspect, new seals, have the heads serviced with new seals, etc. Perform it as a new rebuild to eliminate any questions. How certain are you it’s actually a correct Z engine?

[iluv69s]

As far as cam, carb, timing and tuning, I’d get a hold of Wayne Guinn, especially if you plan on a xram someday. He is a wealth of knowledge on building 302’s and he always shares it.

He has a crossram group on FB. https://m.facebook.com/groups/336597...ibextid=S66gvF

[markinnaples]

Just seems like a good idea to have everything that was built previously without your direct knowledge gone through and double checked as the last thing you want to do is grenade your 302 relying on something that you're not 100% sure of. Just my personal opinion. In the long run, the money you save on trusting the old rebuild may be a waste if the engine wasn't built exactly correctly or if the time has created a weakness that was previously unknown, and you'll end up spending what you saved plus a good amount more on a complete new rebuild or new engine entirely.

[black69]

again, thanks for all the inputs!!! I am new to a 302.

When I wrote this thread, I was already corrupted by this 1968 Road and Track article below that unfortunately gave me the mindset these engines were safe up to 7500. Articles like this one maybe are to blame why so many Z/28s blew. You just get a mindset they were designed to be robust up at the high RPM range of 7000 or so.

Learned alot in the past days.

https://www.curbsideclassic.com/vint...d-shift-point/