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Old L28 rebuild or use as is?


pr20de

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I have a 1983 L28 that I was going to rebuild and put a shaved P90 head on. The engine has been sitting around for a while! Up to 10 years possibly but no way of knowing for sure. It was stored indoors and looks pretty good.

 

I have yet to open the engine but if it looks good and clean, could I get away without rebuilding it? It was supposedly taken from a low mile car that was rear ended. I planned on rebuilding it but I've heard a lot about how durable these engines are and in different situations I've heard people say rebuilds aren't necessary.

 

I would love to rebuild it but I'm having a baby now and if I could save that money it would be great.

 

Obviously at the end it'll depend on how it looks when I open it up, but if it looks real clean what would you guys recommend?

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I'm running a 1978 engine that sat for over 10 years, outside, in the car.  It runs great, has even compression across all cylinders, and blow-by is so low that the inside of the valve cover PCV hose is as clean as when I replaced the hose.  The guy I bought it from got it running again before I bought the car for parts so who knows what prep work he did before hitting the starter.  Probably none. 

 

What do you mean by "open it up"?  And "shaved"?  A shave won't do much for you and will probably just make problems.  You could just take the valve cover off and check for rust and squirt lots of oil around and in the cylinders before turning anything, if you're looking for the least expensive re-start.  Rusted metal, on bearing surfaces like the cam and rocker arms, or in the cylinders, is probably your biggest concern.  If you're going to take the manifolds off, you can check for rust on the valve seats and what you can see in the cylinders.  A few of the valves will have been open, exposing the cylinders to moist air.

 

Some of the seals are easy to get to and cheap, like the rear main seal, if the engine's out.  Check the manifold studs for breakage or corrosion, it's easier to drill them with the engine out. 

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Sounds good guys, I started this thread while on the runway in a plane. I'll give you guys more details now.

 

I have a P90 head that I performed the .080 shave mod, got the .080 shims for the cam towers, shorter valves, 272F cam, etc. I have Triple Webbers, 6-1 Header, etc.

 

The engine is a flat top piston F54 block with a P79 head but I'll put the P90 head on it, so basically I'll be using the block. I'll be able to take a good look at the cylinders and everything since I'll be taking the head off. I just wantd to know if it was ok to keep leave the block as is if it looked ok.

 

 Thanks for the answers

 

At the end if I put it togheter like that and compression is off or anything I'll just take it back out and rebuild it. I don't mind the extra work, I do it myself anyway.

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You're just looking for an excuse, to rebuild it...even though the high probability exists that the rings will be inferior to the Nissan Steel that's in there now.

 

There's a subgroup of automotive fetishists for which "rebuild it" is the first diagnostic response that pops into their head. It's fostered and cultivated by many.

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Oh no don't get me wrong I would greatly prefer not to rebuild it. I was just saying that if it comes down to it, I would rebuild it myself. If anything it's not an excuse to rebuild it but more of a concern that after putting it together with the new head it might not be in as good a shape as it looked. But now I know that it'll likely be good.

I have plenty of experience with other platforms and know that engines will last long times with good care. I've been working with SR20s for more than 10 years and know that a high mileage stock USDM SR20DE will still take 20 pounds of boost with stock internals if taken care of. But I'm fairly new to the L28 and know that some engines are less durable than others. I shouldn't have doubted Nissan though.

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I started throwing 17-21 psi at my used L28 in 1985. It's still in the car today.

 

The oil burning on #5 from sitting filled with water from a typhoon for five years didn't go away until my "ALLRIGHT THEN DIE YOU BASTARD!" 25psi run. Up a mountainside one afternoon. Smoking like crazy at idle and decel going up to the top....not a whiff coming down...or since!

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Definitely replace the studs for the manifolds since it is out of the car.

 

If it's got 100k+ miles, and you're itching to do something, throwing in some new standard size rod bearings and replacing the 30 year old rod bolts with either new  Nissan ones or arp bolts will probably get you another 100,000  miles out of it and ease your mind when revving it.

 

I would replace the rear main and front crank seals.

 

If you're simply going to put it in and start it, you should have no issues as long as you ensure you can get oil pressure right away.

 

You can look into the spark plug holes with one of those harbor freight skinny lights and look at the cylinder walls a little and taking off the valve cover to look for rust on the lobes is a good idea as is pouring some good oil on the camshaft before you crank it to start it the first time.

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Run it!  If you really wanted to go all out, do as others suggested,  replace some studs, gaskets and hoses.  Whatever is necessary, but don't just throw money at it for making yourself feel good.  But since you are going to put on another head I would not tear the engine down at all, run it with old head in place as is to determine if it's good, if it passes then pull it again and slap on the newer parts.  There is nothing on these engines that makes them hard to work on while in the vehicle. 

 

What Tony described is freeing up a stuck ring.  Running them WOT for long periods, and then engine braking (full vacuum at RPM) and repeating several times is the first way I try  to free them up. 

 

I also will spray PB blaster in each cylinder a couple times a day for a week or so, while frequently turning the crank back and forth.  The mild acids in it is not harsh enough to etch aluminum, but does good at softening tarnish/gum in the ring packs.  This is done with engine upright on a stand and cylinder off or on, does not matter.  If I get really particular I will run a bit of Xylene down each cylinder to get some of the PB out, and finish if off with a dab of oil as the Xylene will strip all the lube off.  If you don't have any PB, then just about any light petroleum distillate product will work like liquid wrench, marvel mystery oil, sea foam, chem tool, Kerosene.  Basically any solvent that is capable of dissolving tarnish will work.  Just make sure it has minimal lube before startup, and while you are rotating the engine by hand.  This can be done in vehicle. So no need to do this before startup, only if it smokes a little. 

 

You can prelube the engine by pulling the oil pressure sender or oil filter and injecting oil.  You can do it with a bottle of oil, a drill, fuel line and an air compressor. 

 

It's cylinder pressure that seals a ring, not ring tension.  Cars with stuck rings are either engines that are neglected, or babied it's whole life. 

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I have a similar unknown F54 block engine with flat tops that I'm planning to swap my p90 head onto instead of the p79. The thing is, I bought it all disassembled so I can't really test its condition, but the seller assured me it ran fine before it was pulled. I see that there is some surface rust on the top of the block under the headgasket but it looks fine other than that. What is the best way to get rid of this rust? Can I just sand it off with a block of sandpaper if I plug all the coolant/oil passages first?

 

also, my p90 head has no cam or rocker arms, can I use the "B" cam from the p79 and the p79 rocker arms/lash pads on the p90?

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well its complete, but somebody took the cam out before I got it. I have the right cam, its just not installed.Otherwise I'd take your advice and just not deal with it at all. 

 

So If I use all the wear parts from the p79 and keep them all matched up together there should be no issues moving them to the p90 correct?

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