Head And Pistons

[atkinson40]

Been about a year since I R&R the HG on this beast. Evidently I didn't check the flatness of the head before putting it back on because I was still getting H2O in the oil after I did the R&R of the HG. My little civic blew a HG also giving me motive to fix the easiest of the two. I put more miles on the bike than the cars. :D

 

 

Know issues:

 

1. #3 cylinder wet when I pulled the head this time.

2. Leaking H2O around intake manifold when reassembled last time. The machine shop says they don't resurface that face on the head. I'll check the manifolds and head for flatness there.

 

Yesterday I pulled the head and took it to the machine shop. Today I'll pull the pan to get the pistons/rods out and take them down to have the pistons replaced.

 

Question: I remember something about a ring gap after installing the pistons. What should it be max? Can I buy over sized pistons if its to big? TIA - Kevin

[banzai510(hainz)]

Leaking H2O around intake manifold when reassembled last time

 

this is common if intake bolts to head not tight. Try another gasket. That could have been loose and water getting sucked into the #3 intake. But remeber not to overtighten and strip the alum threads in the head.

 

Ring Gap should have been in the instruction of the rings.

 

If motor never has over heated on you I would think head still be flat,just gasket failed or head bolts lost soem tension

 

rockauto.com

Silvolite has l16 pistons and other have this

 

 

olddatsuns.com

[atkinson40]

Thanks B, Put her up on stands. Unhooked bars to remove pan. Removed pan. Removed bolts on rods. Now ready to measure gaps on pistons as I pull them out. Thought maybe the rings could be identified and over sized put in if needed. -K

 

 

 

[banzai510(hainz)]

if you have oversize pistons it will be marked on top of piston.

1.00mm = .040thous

.50mm =.020thous

 

if no marking I assume stock pistons 83mm L16

 

so you order appropreate ring sets or what ever the machinist says but rings still need to be gapped

[HRH]

You're thinking about this the wrong way. You don't put in oversize rings without oversize pistons, unless you're trimming the rings down to get the proper end gap. Unless you're just planning on bottle brushing the cylinder and re-using the old pistons? Then yes, you can get a set of overbore rings provided you haven't gotten too wide. Just know you'll have to trim quite a bit

 

Another thing you'll want to do is check the cylinder bore for egg-shapedness. A set of snap mics are handy for this. If you're going to bother to take the pistons out, I'd certainly use new rings, especially if the motor is fairly old and those are the original rings.

 

You also may need a ridge reamer, depending on how worn the bore is. This is important to make sure you don't snap the new ring by hitting the ridge.

 

Honestly, I'd give it an eyeball, replace the headgasket, mill the head a little for straightness, call it good and put it back together.

[banzai510(hainz)]

Why are you replacing the rings?If you think this is a head gasket proplem

 

 

I had 2 motors done and I tried always to get away with using the old pistons but I alwasy had one cyl out of round. However I alway had a set of pistons att the machine shop in case of this so no time was waisted ordering or finding oversize pistons.

[atkinson40]

This is the second time I'm doing a HG without putting a single mile on the PU. First time around I reused the pistons and only changed the rings and bearings. Pistons were a bit banged up around the top, but I reused them anyway. I also didn't check the head for flatness and reused with a clean. This time around I'm going to have the head rebuilt and resurfaced before putting back together, and R&R the pistons and rings.

 

 

 

 

I don't see any markings on the pistons. So I imagine they're not over sized? Am I missing something? -K

[banzai510(hainz)]

I will asume its the stock size

[datzenmike]

Yesterday I pulled the head and took it to the machine shop. Today I'll pull the pan to get the pistons/rods out and take them down to have the pistons replaced.

 

Question: I remember something about a ring gap after installing the pistons. What should it be max? Can I buy over sized pistons if its to big? TIA - Kevin

 

The piston size and the cylinder bore are a matched set and no two are the same. If the cylinders were perfectly bored to 85mm and the pistons perfectly machined to 84.998mm everything would be the same. But to mass produce and keep the costs down pistons are graded as being slightly above and below the ideal size. The same is true with the cylinders... some are larger some are smaller than the ideal 85mm. But this is good, as an over size bore can be fitted with an over size piston so that they don't go to waste. The end result is a clearance between the piston and the bore of between 0.0012" and 0.0018" or roughly 1 and 2 thousandths.

 

This is why the guy boring your block should have the pistons so he can measure them and bore accordingly.

 

Now why are you replacing your pistons??? Do so only if the bore is worn past the allowable limit and then oversize pistons must be used and the block bored to a next over size to match. As long as the wear limit has not been reached and the pistons are undamaged, and IF the rings are worn out. Just replace the rings and hone the cylinder.

[atkinson40]

Now why are you replacing your pistons???

 

Pistons were wrecked. Ring groves hosed. Top edges bunged up. H2O in cylinders rusted the rings in place and then the engine was run. -K

[datzenmike]

Hmmm most engines I've opened have cylinder walls that were shiny like mirrors. As for pistons... clean them and inspect the ting lands. As long as they aren't cracked or broken and the sides not scuffed they can be re-used. Assuming they are no good the cylinders should be measured for wear and if over have it bored 10, 20 or 30 over and go with the next oversize pistons. Nissan blocks are pretty tough and with some luck you will only need to hone the glaze off and install new rings.

 

 

 

 

.

[atkinson40]

As long as they aren't cracked or broken and the sides not scuffed they can be re-used.

 

Ring Land sides are scuffed and pushed over bad. Had to file the ring lands to get new rings to fit last time. This time I'll at least put in new pistons/rings. Cylinders look bad from sitting wet maybe? -K

[atkinson40]

Got the head back yesterday. Head rebuild, pistons, rings,rod bearings, and engine gasket set was $450. Figured the investment in the head was worth it. Its a good shop so I didn't question the price. Next time around I'll do the bottom end. Pistons and cylinders are still stock so I can go over sized at least once. They put a refurbished cam in, bearings, valve guides/job. resurfaced the head etc.

 

They told me the head surface was warped and needed resurfacing. This explains the H2O in the cylinders after the last R&R of the HG. I feel a bit more comfortable putting it back together at least knowing there was a reason.

 

Hopefully this pony will become my only driver. I only need to drive about 200 miles a week. The brutal part is idling in line coming back from Mexico. Sometimes the wait is an hour long. -K

[atkinson40]

I can't find the info on ring staggering? I see in the book that the top 2 are staggered 180, but relative to what? Also what about the oil ring gaps? Thanks kevin

 

PS: I've also neglected to mark the rod end caps to the rods when i took them out. Book says something about matching numbers and order. I can't see any numbers that would match end caps to rods or an order. Is there a way to figure this out? -K

[datzenmike]

Rod and cap are stamped on one side down near the bolts. assemble with one number above the other.

 

Pistons are installed with the notch or dot to the front of vehicle. The notch on this Z20E piston faces the rad.

 

 

All ring gaps must not be in the piston pin direction ( front to back of motor) OR in the thrust direction (side to side or 90 degrees to the piston pin) The major thrust direction is on the passenger side of the block so the top ring gap should be on that side and turned slightly to 45 degrees to the front or back. In other words diagonally toward the battery or the windshield washer reservoir. The second ring must be at 180 degrees to the top ring. Top oil control ring should be below the top ring gap. Bottom oil control ring should be 180 degrees to the top oil ring or the same as the second compression ring.

[banzai510(hainz)]

They Put a refurbished Cam in there?

Why nothing wrong with the old one.

YOu know they say new cam ,new rockers or refurbished ones at that.

that could have saved some money there

 

as for block over boring you can go a few time as I had my first L16(83mm) bore out to 85mm(stock L18 pistons so anything inbetween there you can do. My motor was so gouged that I just said Fuck it over bore it to the max(2mm over)

 

if you really think your going to be stuck in traffic alot. Maybe see about getting a 78/79 3 core radiator. I thik they fit the early 620s also just need the top hose as the return is more standard like the other L motors from the driver side. Maybe other people now more about if the later 620 rads fit

[atkinson40]

Thanks B and DM. The gasket kit had 2 in/ex manifold gastkets.

One had round holes so I know it can't be right.

The other has no strip between the #2 and #3 exhaust holes. Is this OK? -K

 

[datzenmike]

Yes.

[atkinson40]

Thanks DM. Went to JY today to find a oil PU that was usable. Mine has a hole in the screen. Anybody have an idea on how to fix or replace, etc. Tried solder but it won't stick. Thanks -K

 

[atkinson40]

Found one at local Nissan dealer. Should have rest of PU built back up by the time it gets here. -K

[Jester]

Please don't take this as an insult, but, I can't believe your going to spend $450 on everything new and NOT bore the cylinders to match your new pistons. Honestly, your asking for a reason to do it again in your near future.

[datzenmike]

Pistons were wrecked. Ring groves hosed. Top edges bunged up. H2O in cylinders rusted the rings in place and then the engine was run. -K

 

A good hone might be enough with new rings but only if the bore isn't already worn past the wear limit.

[banzai510(hainz)]

Hone? Fuck it sandpaper!!!!!!!

 

he be fine.

 

 

I have a spare L16 was thinking of doing a back yard rebuild myself then give the motor away and see how long it lasts. Re ring even with worn pistons ,do it as a experiment

[atkinson40]

The beast breaths again. Picked up the oil PU yesterday and installed it and oil pan gasket. Fired right up once I put some gas in the tank. :rolleyes:

Preliminary observations:

 

1. A couple of slow H20 leaks. One around where hose goes into thermo housing. One down below by the fitting by the alternator.

 

2. Small gas leak where the fitting goes into the carb

 

3. No dreaded oil pan or valve cover leak yet.

 

4. Temp gauge climbed up to about 3/4 of the way. Before with bad head only went about half.

 

5. Noticed some air bubbles through the carb window coming through the needle valve as the float rises and falls to let in gas. I assume I have a leak in the gas line that's letting it suck in air??

 

It did seem to hold its own on the idle at startup after about a minute of holding the peddle at a high idle. I think maybe this must be the high idle adjustment. I only ran it for about 5 mins. Still need to check carb tweeks, timing, etc. I did this on first R&R of the head, but who knows what I misadjusted trying to compensate for the head being bad.

 

Could the temp climb be from only H2O for coolant? Looks kinda rusty down in the rad and I don't want to waste coolant until I feel comfortable I won't have to drain it. It has a new thermostat and pump.

 

What should I do for a flush before new coolant add?

[banzai510(hainz)]

If you said you had a new cam in there ai would have ran it up and down than at a steady idle to help break it in. You should run it that way for about a 1/2 .

 

it might run hot if motor is tight/new.

 

I would just drive it. if it breaks it breaks