Engine rebuild advice? Suggestions?

[rdefabri]

Yeah, isn't that strange? I thought the same, unless it just isn't a 4.11 diff. I've only had the car for about 2 months, and with children it's impossible to get free time

Ok, let's reset the thread. I wanted to get 225 at the crank if I went for the Rebello stroker (at least that's what they advertised). I know my way around cars well enough to know what I can and can't get and how much to pay (I may be a newbie to this forum, but I am no newbie to cars, hot rodding, etc.)

I realize now that the Rebello stroker is not the way to go ($$$). That's why I suggested the 280 crank/rods. With that extra displacement + a good head rework, I have to be realistic about what I can get. Given the $2K budget (I have been told that a Sunbelt job is $1,500 or so) I think 190 at the crank should be attainable or somwhere close to that.

I am curious if I really have the 4.11 gears, I have to take a closer look at it. The thing doesn't move out at all, in fact it's much slower than the Z I had 20 years ago. In fact my 1997 Saturn SC2 is much peppier, leading me to believe a) it's not a 4.11 or there's something wrong with the engine.

My guess is that it's a, since the engine seems to be fine, but then again I need to rip the thing apart to see.

[ZSaint]

I too have built lots of engines. Some I built the old fashioned... I kept breaking them until I figured out how to make the last. I guess we learned from the school of hard knocks. I am wondering if you have one of the "long" 1st gear 5-speeds with the stock 3.36 diff. That will make the Z bog down in a hurry. I guess you can use the old method of counting wheel turns and drive shaft turns to get your ratio. 10 turns of the D/S = ?? turns of the wheel. If you do have a 4.11, your wheel should turn 4 times while the D/S turns 10. Now if the wheel only turns 3 1/3 revolutions, then you have a 3.36. I think the wheel rate is doubled if you have one wheel on the ground. (ring gear/spider gears) It's been a long time since I did a diff like this but I think I have the info you need. We will be curious when you know the ratio. If you do have a 4.11, I haven't got a clue what the problem is.

[rdefabri]

That's certainly one way!!

I could also pull the rear cover and I think there is a stamping inside that should indicate if it's a 4.11. I am pretty sure the diff has been changed, or minimally cleaned, it looks rather new.

The 5-speed is a Motorsport Auto unit. Don't know if they still sell them, but it's not a T-5 from a Mustang or ZX. I am curious if MSA just rebadged or mimicked what was in a T-5, but I am not up to speed on what the gearing was in them.

Here's what is interesting. When I am below 3000 RPMs, the motor coughs and such, but once you get past 3000, the thing takes off. I figured that was due to the cam, I bet the previous previous owner dumped something in there without doing the port/valves/exhaust, etc. It doesn't burble at idle, so it can't be too hot of a cam, but it's sluggish at low revs.

I also noticed it ticks a bit. I know the Z's are known for this, but it seems pretty loud. I have good oil pressure, and it's not smoking, so maybe there's just a need to get that head off and have it done.

It will take me some time. I have to start tinkering with the E-type too -- while quite similar to the Z, it's different enough to scare me more.

[kenz240z]

Have you adjusted the valves, timing & carbs? If it's ticking a bit could be the valves need adjusting. Adjusting the timing & carbs won't yield as much improvement in performance until the valves are set.

I recently looked at a '72 Z with a 4 bbl intake and Holley carb. It had a 5 speed in it, not sure what kind, and I'm not sure about the differential gearing. But, it was quick, it would put you back in your seat when you took off from a start. The guy said the engine was out of a '73 so it would be an L24. The rest of the car was too far gone for my liking, but I've been thinking it might be worth it for the drive train... I know you want to keep the stock engine in the car, perhaps swapping out to a 4 bbl might be an option, though...

[beandip]

To me from what you describe the performance is like , if the engine is in proper tune that is . The engine is over cammed for the gearing . Installing a performance cam in a engine changes the RPM where the engine makes power . A radical cam will require the engine to spool up to much higher Rs to perform at it's best . When you are driving down the freeway / turnpike in 4th gear what are your RPM vs MPH ? This is one thought. If you are concerned with numbers matching and you do not want to install a later engine then I think you need to rethink your 190 HP figures . Especially if you don't have deep pockets. Since the car has been modified already , 5 speed , different diff, and the engine has been modified , numbers matching really is no longer a factor. Now keeping it all stock then yes keep numbers matching . Some day someone may want to strip it down and restore it to origional . This is where the numbers matching come in for show judging. My 2 ¢

[kenz240z]

Rich, I forgot to mention in my previous reply that my engine really takes off at around 3000 rpms, too, seems to be the start of the power band. It is smooth up to that point, no coughing or sputtering, but it's not real quick.

I had the engine rebuilt last spring, it's a '73 L24, but has an earlier E88 head (the original head developed a crack), round top carbies & intake from a '71 and an MSA header & turbo exhaust system. I think the block, pistons, crank & bearings hold up real well on the old Z engines. I could have gotten away with only replacing the head, the cylinders were barely worn, no ridges at the top or anything, a faint trace of the hone pattern still visible on the walls, etc... I spent just under $2k to have the engine rebuilt.

[nwcubsman]

...snip.... I think the block, pistons, crank & bearings hold up real well on the old Z engines. I could have gotten away with only replacing the head, the cylinders were barely worn, no ridges at the top or anything, a faint trace of the hone pattern still visible on the walls, etc... I spent just under $2k to have the engine rebuilt.

I think Kens observation is pretty typical. You can have 150k miles and still see the hone marks on the cylinder walls. The tolerances on these old engines are pretty loose by todays standards.

I have a question form all this talk of putting a 280 crank and rods on an L24 block. Wouldn't you need to do the extra balancing work the same as for a stroker. If you are trying to throw around that extra length at higher 240 type RPMs, I would think the same kind of machine work would be involved as putting the LD28 crank in a L28 block. Please feel free to explain the error in my logic. Are the rods shorter?

[ZSaint]

The tranny ratios are as follow:

4-speed 1st gear - 3.549

5-speed 1st gear - 3.062

You really will have quite a difference in low gear with the 5-speed.

I agree with Beandip. If your car has been modified, why not put a 280ZX engine in the car? I have my original 4-speed, 3.36 diff and 240Z engine stashed away in my shop. If I want to show this car as an original numbers correct model, I will only need to re-install these original parts. If you do not have these parts for your car, oops! I also wanted the car to appear original. I like the look of the original 240Z. I even put the BRE front and rear spook/spoilers on the car. I kept all of the original parts in the engine compartment. It is a 3.0 liter but looks like a 240 (unless you look close!) Maybe you are looking at doing something that you don't really need to do. What do you think?

[rdefabri]

Well, that's the dilemma.

Since it's numbers matching, I like the idea of keeping it original. I could always score a 4-speed and ditch the rear end (what ever it is). I have the slotted mags, and I actually prefer the steel wheel/hubcap combo.

The only other mod appears to be the seats, they have Recaros (which suck horribly).

It's close enough to "original" to restore, but I don't want a trailer queen. I don't care about winning concours events or anything like that, but I do recognize the historical significance of the Z. It's why I bought a 240 instead of a 1977 or 1978 280Z.

To be honest, when I bought the car, I assumed the thing wasn't quite as original as it is. I was fully prepared to modify it heavily. But now I am having second thoughts.

On the subject of the L28 crank, it's definitely different from the LD28. I am 90% certain you can use the L28 crank and rods with no issue (that's essentially what a 260Z is). I'd never put it in without first balancing, but Z cranks are legendary for being balanced.

I think the answer is to forgo the L28 crank, just send the head out for the rework/valves, etc. If I truly have a 4.11, then in stock form, the refreshed engine should move enough for me.

[ZSaint]

Good thinking. Keep her stock and you will continue to love her. Touch up the valves, maybe do a gasket port job, take .020 off the head, put in some new valve seals and maybe a mild camshaft and there you go! (Check the guides to make certain you do not have too much play) It will be amazing how good a fresh head will make your engine run. You are on the right track!

[Arne]

Yup. Had my car still had an L24 in it when I bought it, I'd stick with it. Nothing wrong with a sound L24 for a daily driver.

[rdefabri]

Yeah, since it really purchased it for its significance, I think leaving it stock displacement is cool.

Now I need to score some nice hubcaps for this baby, I love that old school look!