Nissan Rings

millsy

4x4 Earth Contributer
Years ago I heard somewhere that Nissan motors are deliberately built with 'soft' piston rings. The idea being that the rings wear out without doing very much abrasion to the cylinder bores. So it is easier to recondition the engine. Just add new rings, and no need to do a rebore.

Has anyone else heard this story? Is it an old wives tale maybe? Can't remember where I heard it, too long ago. But from various 'observations' over the years I always suspected it might be true.

As an example, the Z motor rebuild information I have found on the Web states that L series Nissan bores are so hard that when it comes time for new rings you can still see the original cross hatch pattern. Although this suggests that the bores are hard, rather than the rings are soft. Either way, both give the same results I suppose.

The reason behind this query is wondering as to why my L28 could be burning so much oil. It has only done 260,000km. My two Holden 'red' motors went so much further - before the rings actually broke up ( in both cases ) - 470km and 407km respectively. I don't recall them causing any great oil consumption before they actually broke.Certainly not as bad as the Nissan L28 in my MQ.

So at the moment I am thinking about three causes - valve steam seals worn out, rings worn out ( or both ), or maybe even just a blocked PCV valve. I thought I proved the PCV valve was OK last year. But I will do it again, just in case all the suction I felt on my thumb was because I put my thumb on the wrong side of the break when I opened up the 'plumbing'!

And I really need to buy a compression tester and do the 'dry' test, and then the 'wet' test. Although wouldn't the wet test cause a certain increase in compression readings even in a good motor?
 
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Split pin

Active Member
Years ago I heard somewhere that Nissan motors are deliberately built with 'soft' piston rings. The idea being that the rings wear out without doing very much abrasion to the cylinder bores. So it is easier to recondition the engine. Just add new rings, and no need to do a rebore.

Has anyone else heard this story? Is it an old wives tale maybe? Can't remember where I heard it, too long ago. But from various 'observations' over the years I always suspected it might be true.

As an example, the Z motor rebuild information I have found on the Web states that L series Nissan bores are so hard that when it comes time for new rings you can still see the original cross hatch pattern. Although this suggests that the bores are hard, rather than the rings are soft. Either way, both give the same results I suppose.

The reason behind this query is wondering as to why my L28 could be burning so much oil. It has oly done 260,000km. My two Holden 'red' motors went so much further - before the rings actually broke up ( in both cases ) - 470km and 407km respectively. I don't recall them causing any great oil consumption before they actually broke.Certainly not as bad as the Nissan L28 in my MQ.

So at the moment I am thinking about three causes - valve steam seals worn out, rings worn out ( or both ), or maybe even just a blocked PCV valve. I thought I proved the PCV valve was OK last year. But I will do it again, just in case all the suction I felt on my thumb was because I put my thumb on the wrong side of the break when I opened up the 'plumbing'!

And I really need to buy a compression tester and do the 'dry' test, and then the 'wet' test. Although wouldn't the wet test cause a certain increase in compression readings even in a good motor?

hey Millsy.
Wet / dry compression testing will give you different readings. It is in the difference of those readings that tell you about your copression.
The biggest killer of oil rings is dirty Air. Did you buy the car new or is it 2nd,3rd,or forth hand. It depends on the original owners before you if they replaced the air filter often enough or did they at any time run the car/motor with out the air filter. Millsy you wont really know until you lift the head.
No I have never heared that piston rings are built softer for nissans. All rings both compression and oil rings will be softer than the bore. Both rings need to expand under the combustion pressure to prevent the majority ofcombustion from entering the sump. A very small amount will always bypass the rings thats why breathers are added to either the rockercover or the side of the block. yesteryears this used to allowed to go to the atmosphere. But today this needs to go back into the intake side to be reburned in the combustion chambers. My old L28 motor that I owned was dead at 90 thousand ks. I rebuilt it and today it has done over 400 thousand ks and still in the family. The air filter gets replaced every 5 thousand and has never had a oiled filter in it I hate them and have always used paper filters for my Air ( I find them safer regarding water intake thats my personal opion any way). I am sure others may have other Ideas but thats what I know. So do the wet and dry compression testing and let me know. you should only have a difference of about 20% no more. Valve stem seals. Well you can tell if they are gone when you are driving and you put your foot down you will have black smoke comming out of the exhaust pipe thats normal its undurned diesel. When you take your foot off the pipe should only have a little whiteish smoke but if its a blueish colour thats oil leaking from your valve stems. Best way to check is get a mate to drive your car and you follow in another and when he accelerates and then backs off you will see and or smell the oil.

Cheers

Peter
 
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millsy

4x4 Earth Contributer
Thanks for all those thoughts Peter. Helped me get my head around a few things a bit better. The 20% figure for example. So I guess you mean that if I get a much greater value than 20% then the compression rings have had it. And of course the main reason for oil consumption would be the oil control rings. They might not be worn, but just choked up with grotty carbon deposits.

I think I have read, or been told, that a blocked PCV valve can also cause big oil consumption. Mine is in the side of the block, as you have said. Will have to have another look and actually remove it to see if it is still 'free', and not blocked. I know the Holden PCV seems to just have a little ball bearing in it, ans you can hear it rattling if you just pop it out of the rocker cover . And I suppose easily test it by blowing through it. Will need to do the same with mine.

Well done on your great run from your L28. Do you remember what type of rings you used. Apparently there are three types - one, or two, being a lot harder than the other. I guess you would only use these if you have done a rebore to get the bores perfectly round again.

I am thinking of just trying to replace the valve stem seals first, without taking the head off. If I can pull this off without stuffing up the timing chain issue, or losing a valve into the cylinder, or maybe even a valve head not reseating due to carbon deposit build up, then it should be a cheap fix. And maybe I will find the seals so stuffed, as I found the front ( timing cover) seal completely chewed out a few weeks ago, that with a bit of luck I will get a good result by just doing that.

Being a mad scientist, I like to just do one thing at a time if possible. That way, if you get the improvement at least you know what the problem was, and can file that bit of proven knowledge away for next time - either for yourself, or to help others with the same problem.

As far as the car is concerned, I bought it 21 months ago at 223,000 km. It used oil pretty badly - about 1 litre per 400km, using 20/50 oil. The previous owner, I think #2 owner, picked it up from a used car lot at about 100,000km 15 years earlier. So he only did about 8,000km per year. The consumption rate improved to about 1200km/litre. But this was probably just because I changed to Penrite 30/70 thick oil.

But on the last three trips around the Victorian deserts it has worsened back to 300/400 km/litre again, even with the thick oil! And on the faster trip back home from Geelong, 600km along the highway, it was about 1 litre for the whole trip, of 40/70 Nulon oil. So I am getting sick of it at this stage. The initial excitement of driving a 4x4 around the bush has worn off, and now its time to do something about it!
 
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Split pin

Active Member
Millsy.
It appears that you are on the right track. It is always better to go from the easiest(cheapest fix) to the hardest (dearest fix). No I dont remember which ones I used re piston rings that was a fair time ago about 4 vehicles lol.Let me know how you go. With your blow by line that comes from either the rocker or block you should only really get a breath of air at idle. If its pumping out well yes you have a significant amount of crankcase compression. With a lot I mean you will feel it pumping out when you place your finger over the end with in a couple of seconds. If it takes a little over thirty seconds to build up pressure then the crank case pressure is OK. (rough bush mechanics).
Again just my two cents worth lol
 

millsy

4x4 Earth Contributer
Thanks Split pin, I will get back to you with those compression readings, and the blowby situation.

There are actually two outlets from the motor. One from the top of the rocker cover into the air cleaner and one from the side of the block to a point on the inlet manifold, just under where the carby is bolted to it. So will have a look at both of these to see whether either of them are blocked, or have excessive pressure.

The manual says that the PCV valve is in the side of the block. Could not see it last time, when I replaced the rubber tubing, so it must be at the back of the 20cm length of steel pipe coming from the block. Will need to dig it out I guess and make sure its OK.

I am still trying to make up my mind whether I just take the head off anyway. It will be a lot easier to work on those valve springs and collets if I have the head out of the truck. It would be easy on a normal car, but this thing is so big! I would be caving my ribs in trying to reach everything. The only other way would be to take the bonnet off and set up a plank of wood across the engine bay as a seat.

So will see what the compression readings say, and what the blowby is like, and if they are both good I have to decide how to tackle the valve seals - head on or head off. Otherwise its staight forward - it needs new rings ( and bearings, and valve seals ) - and so just take the head off.

Mucking around with one of the dinghys this week, fixing up a few cracks in the paintwork before I take it out for a sail on the weekend. So the trouble-shooting on the Nissan will have to wait a little longer yet.


Thanks again for those good tips as to what to look for, Millsy.
 
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