L20 rebuild questions

[screamer510]

From a previous owner, about my "77 200SX L20b:

"The engine was rebuilt and installed at about 102,000 miles. It was 26+

years ago but from memory the cylinder walls were honed and they used new

rings and the original pistons. All bearings, etc. were replaced."

 

The engine now has only 141,000 miles on it, but since the rebuild was such a long time ago:

1. should I be worried about changing the bearings when I replace the piston rings?

2. do I need to replace rod bolts and head bolts (they're the turbo ones) or can I reuse them?

3. I'm not really a newbie on rebuilds, but what else should I look out for?

 

I want it to last!

 

Dan

[datzenmike]

From a previous owner, about my "77 200SX L20b:

"The engine was rebuilt and installed at about 102,000 miles. It was 26+

years ago but from memory the cylinder walls were honed and they used new

rings and the original pistons. All bearings, etc. were replaced."

 

The engine now has only 141,000 miles on it, but since the rebuild was such a long time ago:

1. should I be worried about changing the bearings when I replace the piston rings?

2. do I need to replace rod bolts and head bolts (they're the turbo ones) or can I reuse them?

3. I'm not really a newbie on rebuilds, but what else should I look out for?

 

I want it to last!

 

Dan

 

1/ If the motor runs good just leave it and drive it. If burning oil or poor performance is the reason you want to re-build keep in mind that motors can't be re-built over and over just by honing and replacing the rings.. they do wear out. If rebuilding it by replacing the rings and because it has already been done once before, you should at least measure the cylinder wear. Likely it exceeds the limit and should be over bored and larger over size pistons and rings installed. To answer the question, yes, new rod and crank bearings are a good idea if investing this much effort in a rebuild. If your plan is to just hone and install rings like the last rebuild then don't bother with the bearings you can do all that when you re-build again in a couple of months.

 

2/ rod and head bolts are totally re-usable if undamaged. Clean the threads and the threads in the block.

 

3/ When rebuilding? Worn timing chain, worn out valve seals, Replace the front and rear crank seals (usually included in a gasket set)

[screamer510]

So just keep replacing seals until it is all done leaking? Should I drop the crossmember or lift the engine out for the oil pan? I have the Haynes manual directions, just don't know if there's a preference (can I drop the crossmember only?).

I have a fair amount of blowby, hence I would like to replace the rings. Other than that, the car is pretty good as is. Just trying to be proactive instead of reactive.

@Datzen: I really appreciate all your help and your positive attitude in sharing information!

[ariascarlos1990]

I thinks its easier to drop the crossmember when doing the oil pan gasket in a 510.

[albyneau]

From a previous owner, about my "77 200SX L20b:

"The engine was rebuilt and installed at about 102,000 miles. It was 26+

years ago but from memory the cylinder walls were honed and they used new

rings and the original pistons. All bearings, etc. were replaced."

 

The engine now has only 141,000 miles on it, but since the rebuild was such a long time ago:

1. should I be worried about changing the bearings when I replace the piston rings?

2. do I need to replace rod bolts and head bolts (they're the turbo ones) or can I reuse them?

3. I'm not really a newbie on rebuilds, but what else should I look out for?

 

I want it to last!

 

Dan

 

Hi Dan~ Is there a reason to worry about rebuilding you're not sharing? 141k just isn't that huge a number any more. On the flip side~ why were the rings done @ 102k? Since we have questions with no possible answers from PO, I'll assume a rebuild is justified. Nowhere is the carpenter's adage "measure twice, cut once" more appropriate than in engine building!

 

1. You'll already have the rods out to get to the rings, just as the last guy did~ so they may have already been replaced. It's not that much further to go to either "roll out" the mains (not a procedure I use or endorse), or bust the maincaps loose, and measure your clearances. You're so far in that these couple extra steps don't take that much more time, may cost a bit more for parts~ but in the long run will pay for itself by not "going back under the knife" again. Remember~ you want it to last!

 

2. The quick-n-dirty answer here is yes~ replace all the bolts. You don't know their history. The four main things that'll kill the bolts- any bolts- are improper torque, dirty threads, overheating, and improper application. Has the motor been thrashed or overheated? You'll likely never get a straight-up answer on that one. If one has honest and accurate history on the motor there's little reason to swap bolts~ as long as they're NOT the torque-turn or torque-to-yield types, or you're not gonna take Gramma's '64 Fairlane out on Sundays to the drift competition. Why this example? Early motors had small rod bolts, and high revs is what kills rod bolts (improper application). Their highest load is just past TDC when they have to pull the rod/piston back down on every other stroke. If on a budget I'd swap out the bottom end bolts (rods/mains)first. If you do reuse your bolts, make every endeavor to put them back in their same respective locations. Don't flip rod nuts over.

 

3. Look out for everything. Measure everything. Clean everything twice~ then clean it again. Be a detective~ if you see something funny, ask yourself why? All bolts requiring a specified torque value should have lubricated threads~ oil in the bottom end, antiseize on headbolts and in aluminum.

[screamer510]

Just crawled under the car and wiped off the oil.

First of all, why would anyone paint the oilpan gloss black? :blink:

 

*All* of the oilpan bolts were loose to finger tight to hand tight. Torqued appropriately.

 

The trickle of antifreeze is gone, just some dirt it attracted left behind.

 

I think I'll just pull it and replace all gaskets. Should I mess with taking the head off :unsure: for a head gasket while I'm there?

[albyneau]

Just crawled under the car and wiped off the oil.

First of all, why would anyone paint the oilpan gloss black? :blink:

 

*All* of the oilpan bolts were loose to finger tight to hand tight. Torqued appropriately.

 

The trickle of antifreeze is gone, just some dirt it attracted left behind.

 

I think I'll just pull it and replace all gaskets. Should I mess with taking the head off :unsure: for a head gasket while I'm there?

 

If I pull a motor to replace all gaskets, it's silly in my book not do the head gasket or check rings-n-bearings. Have you done a leakdown test?

[screamer510]

Hmphh.

[banzai510(hainz)]

First of all, why would anyone paint the oilpan gloss black? ?????????

It hides oil leaks better!!!!! esp when block is black also. Its a Optical illussion thing, when guys say your motor is dirty. Its clean to me!

 

oil pan bolts are about hand tite, 5-7 pounds. Butck the stock oil sender unit. Thestock diaphrame ones can leak. If you have a manual gauge then dont worry about it.

I had a stock oil sender leak from the diaphrame side ran down the block ran along the oilpan to make it look like a rear main seal leak.

[screamer510]

OK. The engine got to the point where it would leak almost all the oil out while driving. Mostly on the passenger side.

 

I had done one of the smoke tests. I took the oil cap off of the engine while running and the white steam came out like a choo-choo. Lots of blowby. Looking back, I'm guessing this (and not JUST age) caused so many gaskets to fail in such a grand fashion.

 

Ordered engine gasket kit, thermostat, some other stuff. Spent Friday night and some of Saturday morning taken loose the engine.

 

Today I took the engine out of the car. Everything went well. I did it by myself with a cherry picker. At 20 *F the hydraulic oil didn't cooperate very much, and it wouldn't pump at all.

 

 

 

 

 

 

 

Took the engine apart, down to the cylinder head. It had been polished in the front of the ports some, and probably shaved ,015"

 

 

 

 

 

Everything looked good with all the other parts. Some minute sharp metal bits in the oil pan. I found the cause of my blowby. #4 piston has a chunk out of the top ring land, and a gouge in the piston top, along with evidence of something rattling around in there.

 

 

 

Everything bagged and labeled, sorted and stored in the barn. It warmed up to 30*F by the time I was done.

 

So, I guess I'm going to replace the pistons Better to solve the root cause of the leaks rather than just applying a temporary fix, right? I'm trying to get this done before too long so my wife doesn't kill me. She wasn't really happy that I took the engine out. One of her stipulations in buying this car was that there would be no engine swaps (VG, KA, SR, etc.). I had to explain to her that this was necessary, wouldn't take long, and was not changing the engine out.

 

How can I do this the cheapest way possible????

 

Thanks for everyone's help and input.

[screamer510]

Just to verify:

a 0.020" oversize piston would only fit in a rebored cylinder bore, correct?

Gotta get the cylinder bore measured this week.

[banzai510(hainz)]

a 0.020" oversize piston would only fit in a rebored cylinder bore, correct?

yes

 

looks like alot of pinging on #4 or bouncing of soemthing in that bore

[screamer510]

Pinging (pre-detonation), foreign debris, valve clearance issues. What else could cause the piston to break like that? There is no damage to the cylinder hear, combustion chamber, or valves in #4 cylinder.

[ggzilla]

If I pull a motor to replace all gaskets, it's silly in my book not ...check rings-n-bearings.

 

You can more easily check those before you pull the motor:

 

* Bearings: Check oil pressure at idle. Datsun spec I think is 17psi. Rev it, listen for taps or knocks. Drive it an listen for taps or knocks. No problems = good bearings. Many Datsun engines go 300,000+ miles with still good bearings.

 

* Rings: Do a wet & dry compression test. Plus a smoke test. Just as likely as the rings to cause smoke is the valve guides.

 

 

If I pull a motor to replace all gaskets, it's silly in my book not do the head gasket

Why bother? The head gasket never blows if you torque it every 24 months/24K miles like the owners manual says (and if you don't overheat the engine).

[ggzilla]

Don't try to fix it "the cheapest way possible", instead do what's needed to do it right. But you don't do more than that.

 

 

So, I guess I'm going to replace the pistons Better to solve the root cause of the leaks rather than just applying a temporary fix, right?

Totally right.

 

A chunk out of the piston ring land can cause massive blow-by. Your rings might even still be good! If you did a compression test and both wet & dry readings were good, then the rings are good.

 

Measure the bore for out-of round. If that's good you only need to replace one piston. If it's a stock Datsun piston, just get another like it. It should have some numbers on the underside. You can even swap brands if the dish and the weight match up. You can grind some down if it weighs a little too much (this is the standard blueprinting procedure, it's not a cheap-out).

 

Datsun head bolts are reusable and unless they are corroded or damaged, I would just reuse them. Rod bolts are your choice. Datsun says the are reusable but Nissan Competition said they are not!

[screamer510]

Borrowed a dial caliper from my wife's uncle, who happens to live in town.

Everything measured out with the cylinder bore to indicate that the cylinders have not been bored. Between the "3.3451 - 3.3470 in" from OLDDATSUNS.com. They all look good, except for some carbon buildup at the top of the bore. There is a lot of cross hatch still evident.

 

Also, on a related note, I somehow overlooked this yesterday (maybe it was the cold?), but the #3 cylinder top has a big gouge in it like it hit a valve. I'm wondering if this could be what caused the lash pad to jump out of the retainer last year, under the previous owner? All the valves looked fine, no damage to any valve, seat, or combustion chamber. Intake = 1.645" and exhaust = 1.375" for reference, does that indicate it is a stock U67 head with stock valves? Also, the intake ports have been ported out to 1.50".

 

What would make that happen? Valve float, a weak valve spring, lack of valve lash adjustment, ???

 

So I need to find some standard size pistons, not just one for the #4 anymore. Can I use an L20b piston from a 610, 710, 720 etc. if my L20b is from a 200SX? RockAuto only lists oversized for my engine, but many many options for those other vehicles that also had an L20b.

 

Making progress! Thanks for everyone's continued discussion! You are the best

 

Dan

[datzenmike]

Borrowed a dial caliper from my wife's uncle, who happens to live in town.

Everything measured out with the cylinder bore to indicate that the cylinders have not been bored. Between the "3.3451 - 3.3470 in" from OLDDATSUNS.com. They all look good, except for some carbon buildup at the top of the bore. There is a lot of cross hatch still evident.

 

 

Yes, however....

 

Standard factory pistons range in size from 3.3459" to 3.3478"

Standard factory bores range in size from 3.3465" to 3.3484"

 

This means that if you get a 'largest' piston (3.3478") even if within spec, it won't even fit in the 'smallest' bore, (3.3465") even though it is within spec. On top of this you need from 1 to 1.8 thousandths of clearance piston to cylinder wall.

 

I believe Nissan grades and stamps (1 to 4) their pistons according to size so that a 'small' bore can be quickly fitted with an appropriate 'small' piston

[EricJB]

Calipers aren't going to be accurate enought to reley on. You will need a bore gauge. I wouldn't trust a familiar pair of good quality calipers any closer that + - .003. and you need to measure the hole in several areas, not just the top. Also check for egg. But yes, it is standard bore.

[screamer510]

I'll pull the pistons and look for a part number to cross-reference with Nissan parts department to determine the correct piston diameter. Then I can get a bore gauge and accurately measure the bore in the places mentioned in olddatsun.com's tech links, like 10%, 30%, and 60% of the stroke in the bore to check for wear, out-of-round, etc. Then I can take that information when looking for new pistons.

 

Sound like a good plan?

 

Dan

[screamer510]

Yes, however....

 

Standard factory pistons range in size from 3.3459" to 3.3478"

Standard factory bores range in size from 3.3465" to 3.3484"

 

This means that if you get a 'largest' piston (3.3478") even if within spec, it won't even fit in the 'smallest' bore, (3.3465") even though it is within spec. On top of this you need from 1 to 1.8 thousandths of clearance piston to cylinder wall.

 

I believe Nissan grades and stamps (1 to 4) their pistons according to size so that a 'small' bore can be quickly fitted with an appropriate 'small' piston

 

Do those numbers make sense, because I must be missing something. I can't say for sure what's going on, but I somehow doubt Datzen is wrong...just takes me a minute to wrap my head around it.

If I take a small piston, 3.3459+0.001=3.3469" or 3.3459+0.0018=3.3477", and 3.3468" and 3.3477" are both < maximum bore size of 3.3484"

 

But no other piston size seems to measure small enough with a clearance between the cylinder wall to fit into any of the bores

 

large piston + gap = large bore

3.3478+0.001=3.3488">3.3484" or 3.3478+0.0018=3.3496">3.3484"

 

...and where on the piston would the "grading" be stamped, presumably the skirt or underside of the piston?

[datzenmike]

If it's stamped, it's usually on top. But does not say what the exact size is. It would have to be measured.

 

Getting the next oversize and taking the pistons to the shop that is over boring the block is best. The machinist will accurately measure each piston and bore the cylinder for proper fit.

[docbainey]

[

So I need to find some standard size pistons, not just one for the #4 anymore. Can I use an L20b piston from a 610, 710, 720 etc. if my L20b is from a 200SX? RockAuto only lists oversized for my engine, but many many options for those other vehicles that also had an L20b.

 

Making progress! Thanks for everyone's continued discussion! You are the best

 

Dan

 

Check Summit Racing

 

http://www.summitracing.com/search/Part-Type/Pistons/?keyword=pistons&kr=pistons

[banzai510(hainz)]

silvolite website

hard to seach they cahnged it around. call them for a vendor that sells as they dont sell direct

I got a set for 76 $ shipped about 5 years ago.

http://www.kb-silvolite.com/silv-o-lite/spistons.php?action=Mfg4l&mfg=Nissan&Div=Nissan&l=1952

 

9048 is what you want

[screamer510]

silvolite website

hard to seach they cahnged it around. call them for a vendor that sells as they dont sell direct

I got a set for 76 $ shipped about 5 years ago.

http://www.kb-silvol...v=Nissan&l=1952

 

9048 is what you want

 

 

Is that a universal part, based on what Datzen says, there may be different.

 

 

What is the going rate for a 0.020" rebore on a bar L20 block?

[screamer510]

silvolite website

hard to seach they cahnged it around. call them for a vendor that sells as they dont sell direct

I got a set for 76 $ shipped about 5 years ago.

http://www.kb-silvol...v=Nissan&l=1952

 

9048 is what you want

 

 

Summit Racing has them,Silv-o-Lite/KB pistons looks like around $102-$115 for a set.

 

Rock Auto has a +.020 for $21, but I have to consider the price of boring, etc.