L24 teardown opinions wanted

[Dershum]

I'm working on tearing down the L24 out of my 71 240, and was hoping some of the more experienced folks (which is just about everyone here) might be able to give me their opinions.

 

In looking at the head, it's pretty clear the rear 3 cylinders are running way too hot. The rear carb was definitely not flowing enough fuel, but I didn't think it was quite this bad. I'm planning to replace the valves/springs/seals, but I'm not sure of the condition of the cam. There's no obvious damage to the toes of each lobe, and I'm assuming that the polished centers with darker bands on the sides is simply from the pads on the rockers keeping the lobes polished on the inside. There's no grooving/scrape marks, and no other damage I can see, however on the cam itself there are pretty big scrapes that look like they were just from the original casting, but I'm not sure if that's supposed to be the case, or if at some point something was loose in the head and scratched the surfaces.

 

On the block side of things, I'm pretty sure a full replacement set of pistons is in order, along with new rings, but I don't see any damage to the bores as of yet. I need to pull the pistons out before I can see everything, but other than the (massive?) carbon buildup/scoring on the tops of the pistons, nothing's jumping out at me saying "omg, the block needs replacing".

 

Thanks for any help in advance, and please be kind..it's my first time

[cygnusx1]

Those cam scrapes are a product of the de-burring process. They ground off some of the casting flash, after the casting was done at the factory. May as well rebuild it while it's apart. You can measure the pistons and the bores to see if they are reusable or you can spring for a full rebuild kit. I got mine from www.rpmrons.com. I sent the head out to a local machine shop to get new valves, seats, and a complete checkup.

Edited October 27, 2011 by cygnusx1

[Dershum]

Those cam scrapes are a product of the de-burring process. They ground off some of the casting flash, after the casting was done at the factory. May as well rebuild it while it's apart. You can measure the pistons and the bores to see if they are reusable or you can spring for a full rebuild kit. I got mine from www.rpmrons.com. I sent the head out to a local machine shop to get new valves, seats, and a complete checkup.

 

I was planning to at least take the block to be honed and checked, and I was also thinking about having the head inspected and a valve job done. What I'm wondering is if the bores are OK, would they measure them and let me know if I need oversized rings or not? I'm not terribly familiar with re-ringing pistons, but I'm guessing that if the bores are OK and just need to be honed, I would just need replacement stock-size rings, or possible _slightly_ oversized ones to compensate for any wear?

 

I was also looking at the rpmrons site a few times, but it seems like $614 for a full rebuild kit (pistons, rings, camshaft, rockers, springs, valves, timing set, etc) seems too good to be true. Is there something I'm missing, or is it really the deal of the century?

[duragg]

Once they measure the bore and compare that to the piston they know the clearance and you can decide what to do.

When I rebuilt my F54 over the summer the clearance was more than I wanted (.004" if I recall?) so we honed out to the next size and I used +1mm pistons and appropriate rings.

 

See if your pistons have any mark on the top now like ".50" or something similar.

 

For sure the valve work is worthwhile so you don't end up with a smoker. Keep everything on the valves in labled bags so you know which hole they came from.

 

looks like fun! When I did mine it was the first engine I rebuilt (with a little help from some ringers).

[Dershum]

I was planning to go ahead and replace just about everything. Pistons, valves, springs, cam, timing components, etc. Should I still save the valves for reasons other than diagnosing possible problems with the head/block? I wasn't planning to re-use them, especially if I just get a master engine rebuild kit from rpmrons.

[Xnke]

If you're going to do it, do it. There is no economy in rebuilding just the bottom end, or just the top end.

 

If you re-ring the engine, but dont' do a valve job, it'll surely smoke, or you'll burn a valve. (usually burnt valves result from the higher compression from the newly finished bores, but less-than-perfect valve seal.)

 

If you do a valve job, things are slightly more relaxed concerning the bottom end...but you are liable to end up using oil or with excessive blowby after a few hundred miles.

 

I spent a grand total of 858$ to completely rebuild my engine...including bearings, pistons, rings, boring and honing the block, all gaskets, oil pump, water pump, bought a cylinder head core, ported the core, installed new valves and valve springs, and a reground cam and rockers, new valve stem seals and valve guides, and a complete valve job. It is really not that expensive to do, if you are doing the assembly and setup work, and you are only farming out the bore+hone, and the valve job. My machine costs were 120$ for the bore+hone, which included checking the block for cracks and wall thickness and checking the mains, and 257$ for the complete valve job, which consisted of new valve seats on the intake, five angle valve job, seat ID's machined out to my spec'ed size, and new valves fitted and normalized for stem length. Yes, I got a smokin' deal on the valve job. I was expecting 300 to 350$ for a real performance job, with the extra work I spec'd.

[Dershum]

Xnke, that's exactly what I plan to do. For now I really want to take it back to stock (or close to it) without trying to do anything terribly performance related. I'm really still learning about engine rebuilding, and I figure if I'm going to do break something or do something wrong, I'd rather do it with stock components. That way I at least have a good point of reference as far as what the stock specs should be. Plus then I'm not breaking an expensive performance part by not knowing what I'm doing wrong.

 

I'm looking around now in the area to see what kind of machine shops are available. There's a 1/4 mile track near here (Island Raceway) so there are a few performance shops around, but I'd imagine they cater mostly to the domestic market...taking them an inline six out of a Datsun/Nissan will probably get me laughed out of the shop. Any recommendations on what I should look for or avoid in selecting a machine shop to do the work?

[Dershum]

Thought I'd add a little update. I managed to break down most of the rest of the short block, and got the timing cover, chain, etc., off, and also pulled out the pistons.

 

Of particular concern was that when #1, #3, and #5 came out, the top compression ring was broken. They literally fell off as I slid the pistons out. Something tells me that's not a terribly good thing, but I took a good close look at the cylinder bores and I don't see any scoring or gouges...they're all smooth as a baby's butt and I can still see the cross-hatching from when they were either re-honed, or originally honed at the factory (no idea if it's ever been rebuilt).

 

Finally, in the category of "things I'd prefer to not find in the oil pan", check out the attached pic.

[Pharaohabq]

Wow Strange stuff to find in the oil pan, I wonder what they were drilling to drop that in there. Sure seems like they wouldn't want that in there, That's a really good argument for those magnetic oil pan drain plugs. (Also a really good idea to use one when you're breaking in a rebuilt engine. The tiny shavings from when things are seating, is actually a good amount, and keepign those out of the bearings is always a good idea. It's cheap insurance I'd say. Weird they's leave that bit in there.

[Xnke]

Scotchbrite your piston tops, that can you if it's been rebuilt. Look for piston oversize markings, and check the bearing journals for size. Measure the head thickness, within a thousandth of an inch. There are inexpensive tools to do this, and you'll need them. Check for valve wear, and measure the valve margins...regardless of condition, if you have less than a 1mm valve margin I'd not use it. Check your bore diameter, at the bottom of the bore, and about a 1/4" down from the top of the bore. Check both side to side, and front to back.

 

The broken piston rings are probably signs of detonation. You appear to have a 2nd generation E88 head, which is an open chamber, and normally runs about 8.8:1 compression. Did you run regular gas in it, or when it was running, did you hear any pinging or knocking?

 

Don't be afraid to be laughed out of the machine shop. The shop that did my work was full of big domestic V8's, laying all over the place. Take the time to talk to the machinist, get a feel for him. If you feel like he's going to just run it across the belt and call it good, don't use that shop. If you think he's going to take the time to measure, setup, and do it right, then use that shop. Don't let machine cost be the determining factor; but be ready to spend the money when you find the shop you're comfortable with. Look for guys who have been doing it from the 70's and 80's, when the L was a common Nissan motor.

 

Either way, rebuilding an L is not a bad job, just keep it all layed out in order and measure it up. Keep tolerances fairly close to the Nissan spec, but remember it's better to be a thou too loose than a thou too tight.

[Dershum]

Scotchbrite your piston tops, that can you if it's been rebuilt. Look for piston oversize markings, and check the bearing journals for size. Measure the head thickness, within a thousandth of an inch. There are inexpensive tools to do this, and you'll need them. Check for valve wear, and measure the valve margins...regardless of condition, if you have less than a 1mm valve margin I'd not use it. Check your bore diameter, at the bottom of the bore, and about a 1/4" down from the top of the bore. Check both side to side, and front to back.

 

The broken piston rings are probably signs of detonation. You appear to have a 2nd generation E88 head, which is an open chamber, and normally runs about 8.8:1 compression. Did you run regular gas in it, or when it was running, did you hear any pinging or knocking?

 

Don't be afraid to be laughed out of the machine shop. The shop that did my work was full of big domestic V8's, laying all over the place. Take the time to talk to the machinist, get a feel for him. If you feel like he's going to just run it across the belt and call it good, don't use that shop. If you think he's going to take the time to measure, setup, and do it right, then use that shop. Don't let machine cost be the determining factor; but be ready to spend the money when you find the shop you're comfortable with. Look for guys who have been doing it from the 70's and 80's, when the L was a common Nissan motor.

 

Either way, rebuilding an L is not a bad job, just keep it all layed out in order and measure it up. Keep tolerances fairly close to the Nissan spec, but remember it's better to be a thou too loose than a thou too tight.

 

Wow...lots of good feedback, thanks much! I've been keeping everything really organized in the tear down. Everything is separately bagged and tagged as to where it came from, the pistons were all pulled out individually, and I kept the bolts and bearings all in the correct places as I pulled them out.

 

In terms of markings on the pistons, what should I be looking for? I assume they'd be on the top, but I'm not sure what I'd look for vs. a stock piston.

 

I've been running premium only in it since I got it, but no idea what was done before that. The PO wasn't terribly good to it...basically kept it running (barely), but didn't do things like check the timing, fix the wiring issues, or much else. The oil that came out of it when I first got it was the nastiest stuff I've ever dealt with when changing engine oil, and the stuff after about a thousand miles or so wasn't any where near as bad...so no idea how often it was changed or even looked at.

 

 

In the beginning I didn't hear any detonation, but it started to knock near the end, so I didn't drive it much at that point. I tried to richen out the mix on the rear carb as much as I could, but it wasn't flowing as well. I definitely need a rebuild there, and I'm planning to go with Ztherapy.

 

According to the head stamping, it's an E31, but the block is a P30. If I'm reading right (http://datsunzgarage.com/engine/) it's not a stock pairing. The block (at least) isn't original, since the serial number doesn't match the VIN of the car.

 

Thanks again for all the guidance, I really appreciate it! I'm hoping to get the rest of the block and head torn down this weekend, and (depending on this freak snowstorm we're supposed to get) going to take the head, block, and a few other bits to the local carwash to pressure wash them off before looking around for a machine shop.