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l20b Engine Find Suggestions


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Does anyone know of a place other than junkyards to find a decent l20b engine that I can swap out of the engine that I have on my 1981 datsun 720 Automatic(which yes, it should have the Z22 but for now it has an l20b with a U67 head). The reason I say this is because my engine runs very poorly, burns a substantial amount of oil, and in the morning at startup, it smokes a ton of blue smoke. The head gasket and new valve stem seals have been recently replaced and the only thing that I can think of other than having this much smoke  is having bad piston rings. Also, it has become incredibly difficult to start and it feels as when the engine is cranking initially, it doesn't sound like the engine is doing much compression hence possibly having bad piston rings. Anything would be much appreciated.

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There is the remote chance that it has the wrong dip stick from the engine swap. Next time the oil is changed, put it the correct amount and see what the dip stick says. It might be over filled with oil. That, will smoke.


If compression is below 150 plus the smoke from worn rings have it rebuilt. Swapping in a totally unknown engine is a crap shoot. There are places like Jasper that sell reconditioned engines and you turn in the core for exchange. Not cheap but you have a new engine.

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The only source for a good running L20B is going to be classifieds. Any shop that has one is going to tear it down to use it as a core. Rebuilding an engine has a steep learning curve, but on an engine of this vintage, that's really your only option, unless you want to pay someone to rebuild it for you.


For what it's worth, my experience has taught me that most engine shops don't know the finer points of building an L series Datsun motor. You need a specialist, and that comes at a price.


If the engine isn't damaged, it's possible to re-ring it and give it some new gaskets. Top it off with a quickie valve job and you should have a sound, reliable engine. I have built L motors where the only new part was a head gasket, and had them run great for years. That type of rebuild can be done in a day, if you have the knowledge.

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Ok, thank you guys for the advice. I'll look into buying a complete rebuild kit after I check the compression readings on a cold engine, and after I add some oil to each cylinder. Also I will verify just to be certain if the dipstick was swapped from the engine that was previously in it.

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whats the timing of this motor? Using a timing light

have you check the rocker arms to make sure they set correctly. If you have a few that are on the tight side. esp the exhaust that will also hurt starting.


if you burn a quart of oil in 2 weeks I would say yeah your rings are shot


since your in Pasco theres got to be a L motor around in back of a field or farm somewhere EZ!!!!!


I would dial motor up to TDC on zero deg then look at my cam timing see where that is at.  look for chain wear. but 99% its fine

Edited by banzai510(hainz)
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