Plan to pick up some plastigage this afternoon and disassemble the crankshaft. Reading the information in Tech Wiki, the "bearing crush" tolerances is what I will use to determine if the bearings are within specs? And reading the Haynes shop manual the tolerances for end play is only at the thrust (center) bearing? Please explain the "bearing clearance" tolerances. Also I notice a slight lateral movement in both directions on all of the connecting rods, but not up and down. Is this normal? Engine has about 130K miles. Thanks for the help.

Bearing Clearance
* Main: 0.020 to 0.062 mm
* Rod: 0.020 to 0.050 mm
Main Bearing Journal diameter
* 49.951 to 49.964 mm
Crankpin Journal diameter
* 44.974 to 44.961 mm
Journal Taper and out of round
* measure multiple spots
* less than 0.03 mm
End-play
* crank thrust: 0.05 to 0.15 mm
Bearing Crush
* main: 0 to 0.03 mm
* rod: 0.015 to 0.040 mm

Bearing crush is only used when installing new bearings.


To examine used bearings, measure the clearance using the plastigauge. If the measured clearance is within the spec range, they are good. Too much clearance and the oil pressure drops. Too little clearance and they could bind.

Datsun Factory Service Manual (see Bearings)


Also give them a quick visible inspection. No scoring, no pits, no scratches, no heat marks ... they can be reused

Some shade-tree mechanics don't want to use plastigauge -- in that case they measure the journals and bearings directly using micrometers then subtract the difference to get the clearance. Or if you are checking a crank that is not in the engine, you can measure it directly. Otherwise you can ignore the measurement specs and only use the clearance figures.

Ok understand DD. The bearing clearance specs is what I compare to the plastigauge results. So how about the side to side play on the piston rods? It's not much but noticeable. Is that normal?

It's normal. Did the engine have any audible bearing tapping? If so it warrants extra checking. But if the engine was quiet, well remember the bearings can go 500,000 miles so no worries. They are big bearings and made of super-strong material. Most bearing failures are the result of lubrication problems either running out of oil, old oil, or contaminants getting in the oil, and not from old age

Well no idea how it ran. I pulled it from this salvage 1981 210 wagon. I had no intentions of getting another A15 motor while I was looking for a 5 speed 60 series transmission but what caught my interest was the oil filler cap. Is this a JDM motor? I popped the valve cover off and it had the rare H89 head (single spring). So took it home. A problem I see with this motor is that the water pump was seized with alot of crud. And when I went to take the head off, one of the bolts (#1) was very difficult to remove. Finally worked it loose. The bolt also had some crud on it. Likely overheated and maybe caused damage? The head surface is flat and dont see any signs of a cracked or damaged head. The motor turns freely and the crank has less end play than my other A15 motor so I plan to go through it and give it a refresh. Still can see the original cross hatches. I will be taking it to a machine shop to get it cleaned with a good detergent (no harsh chemicals) and they will spec out the bore for me. If its good, I will have them hone it out. Its a toss up to go with either the GX head or H89 head but will likely stay with the GX head for this build.

If this is a JDM motor any idea how it ended up in North Texas??

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G,
The Japan home market has a registration tax system that taxes cars progressively higher as they age. As a result, there is a large supply of decent used cars that are scrapped and the low mileage engines are imported into this country. I bought a couple of used import engines and transmissions for our Civic and Accord in the 90s. There were used Japanese engine & trans sellers in Houston so I am sure they were/are in your area as well. That's how the engine came to be in the car in the junkyard where I found my H89 head. That's the reason I tell everyone to look under the valve cover of any Datto A series when visiting the junk yard. Ya might get lucky.

Yes it's probably a "good used Japan motor" that they sent over by the container loads in the 1980s and 1990s.

* it might be a round-port H891
* Are there any signs it overheated? Rust scale & stuck bolts indicate that someone ran plain water in the engine. So flush it out well or have the block cleaned

I still have the GX motor that we got from one of the engine importers in 1991, it's my spare "race" motor. The A15 motor in the car now was an import as well. I don't know the ratio of cars with import engines but I have 3 oil caps like the one pictured that came off extra motors I ended with.

I am always reminded, when posts about checking clearences come up, that I am so not an engine builder. I have more than once simply measured the bearing thickness with a mic or caliper and if it was remotely close slapped it back in. All of the bearings in the A15 are new but on the A12GX I never even looked at the bearings, after 18 seasons of abuse the rings & bore finally wore out so I relented and changed the bearings. (Don't tell anyone I actually checked them properly)

Tom

58custom (Tom)...thanks for the explanation on the imported motors. And I did take your advice (pop off the valve covers) and got lucky with this H89 head. I have enough parts now to build two engines.

Tom...I have been thinking about building a race motor with the spare A12 I have. But will save that for another day. Have my hands full at the moment with the A15 conversion on the MG. Bearings look ok for the A15 but may go ahead with replacing all of them. There are kits on ebay that are fairly reasonable which includes rings and bearings. Is there another supplier that sells good rebuild kits? Rockauto seems to be popular. Want to make sure I get quality parts.

DD....oval ports for the H89 head pictured on the bottom in the photo. Measures approximately 35mmx29.25mm(+-), compared to the GX 39mmx30mm. I read Tech Wiki and it says 36mmx30mm for the GX head?? I dont think this one was modified. Used calipers on the manifold side to measure the oval ports. Should I be measuring on the inside of the port?

H89 head is closed chamber and is highly sought after by MG enthusiast for the nissan conversion. I got real lucky finding both in the North Texas area.

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The lower head looks ported

Yes, measure the head, as the manifold can be different sizes. When assembling have "port matching" done to even up the size difference between head and manifold. Or not (most folks don't), it's worth a little bit of HP.