NS90A rebuild

[jjreds]

Center cylinder 0 psi, I heard a pop when it happened I think it sucked something thru the crankcase and broke a ring. Anybody ever seen this?

Do I really need to drop the gearbox to R&R the power head?

First timer. Thanks guys.
Jim

 

[pvanv]

Re: NS90A rebuild

Haven't seen it, but it's possible. May have cracked a piston or ring.
Yes. You will disengage the powerhead. Then disassemble and inspect everything.
May as well service the water pump while you have everything apart.

 

[TOHATSU GURU]

Re: NS90A rebuild

You don't have to pull off the lower unit....Due to the age of the engine, cost of repair may exceed it's value.

 

[jjreds]

Re: NS90A rebuild

I took the head off to inspect it, the piston is intact, at least the crown is, something def came thru lots of marks in the comb. chamber and a mark on the edge of the exhaust port. Does the crank use a caged bearing on the rod? I don't see any breakdown of the crank assy in the parts book. I'm wondering if a rod bearing started to come apart? No knocks or rattles prior.

Checked with bore mic bottom cyl is the worst way out of round and +.018" in the worst spot. No scoring or AL in any of the bores.

Any tips/shortcuts to get the powerhead off and on the bench? Going to tear down tomorrow and inspect.

Thanks again,
Jim

 

[pvanv]

Re: NS90A rebuild

Jim,

The crank and rods are serviced as an assembly. If you have a bad rod bearing, I would replace the whole motor, as the cost to repair would far exceed the value of the repaired motor. Although... there is a shop in the Carolinas that can press the crank apart and together if needed, allowing access to the bearings.

If the only damage is at the cylinders, you could replace pistons and rings with oversize, after the block is bored, but again, you are approaching diminishing returns on the parts investment.

Did the debris crack the reed valve? If so, a broken reed could have wreaked havoc on its way through the motor.

 

[jjreds]

Re: NS90A rebuild

I will definitely check the reed cages. I can't get the PH to break loose.
(8) bolts around the bottom are out and all hose, wire and linkage preventing removal are unhooked/ out of the way. Is there a trick to getting them to separate?

 

[pvanv]

Re: NS90A rebuild

There is a base casting between the block and the driveshaft housing. Is that unbolted? If so, you need a solid tug, assisted with a lever or two to break the 25-year-old grip of the gasket.

 

[jjreds]

Re: NS90A rebuild

Thanks for the tip she split hard!!

 

[TOHATSU GURU]

Re: NS90A rebuild

Is that an old Nissan boat?

 

[jjreds]

Re: NS90A rebuild

Yes it is.

Both center crank bearings are gone. I already bought the pistons a while back and the bore job is $75.

I want to talk to the guy in the Carolina's before I decide what to do. What's the co name?

Anybody got a used crank to fit ns90a?

Thanks guys.
Jim

 

[pvanv]

Re: NS90A rebuild

IIRC,
Ackermann Marine Services Inc
2137 Wrightsville Avenue
Wilmington, NC 28403-0270

If they will press/unpress the crank, you may be able to service the bearings independently, but you will need to source the bearings -- they are not listed in the Tohatsu parts catalog as separate pieces. Otherwise, you will probably be looking for an old 90A in a salvage yard, because the new part (available from any dealer, including me) is costly: 3B7000300M CRANKSHAFT $1589.95

 

[jjreds]

Re: NS90A rebuild

Thanks. Talked to Ken @ Ackermann. Checking my options. Do you happen to know if the 6208 bearing listed in the parts on the PTO end of the crank is the same as the two center main bearings? Or what those center bearings are?
Jim

 

[pvanv]

Re: NS90A rebuild

Not for sure. Elvin may know.

 

[jjreds]

Re: NS90A rebuild

NS90A Main Bearings:
Mag bearing Koyo .36NQ5238UWII
Center (2) Nachi 6307-S14
PTO Nachi 6208-S10

Rod Mains - TBD

Will use the std SS versions of the Nachi's with Loctite 641 instead of the anti-rotation pins and the mag bearing from Tohatsu.

 

[jjreds]

Re: NS90A rebuild

Just dropped the block off at the machine shop to get the pistons fitted, I'm using Wiseco .030 over. I asked them to chamfer the ports so the rings aren't traveling over any sharp edges.

We'll be pressing apart the first journal this weekend to ID the rod bearing.

Looks like I'll have ~$850 in this by the time it's done incl. water pump.

Gearbox lube is dry and clean.

Any known issues in gearcase on these motors I should inspect?

Thanks,
Jim




.

 

[pvanv]

Re: NS90A rebuild

Nope, but at that vintage it might be wise to install a seal kit in the LU. If you do reseal the LU, don't forget the o-rings for the cam rod bushing.

 

[jjreds]

Re: NS90A rebuild

OK thanks Paul, would I have everything I need in 3B7-87321-0 Lower Unit Gasket Kit or are you saying to order the o-rings as well?

Thanks,
Jim

 

[pvanv]

Re: NS90A rebuild

The LU gasket set is complete; just don't overlook the o-rings

 

[jjreds]

Re: NS90A rebuild

I've ordered the LU gasket set, I'll tear into that this weekend. We didn't get into the crank yet as the shop was busy with production work. Thanks for all the tips. The fuel lines on the PH are in good shape with no cracks and pliable. The oil lines however need replacing. If I'm not mistaken they are 2mm and 10mm ID PVC, correct? And it looks like I can drive the pump with a drill to prime the lines after assy before starting, is that how you would do it?
Thanks again,
Jim

 

[pvanv]

Re: NS90A rebuild

Jim,

Oil line is available from any Tohatsu dealer. So is a Factory service manual. In that and the owner's manual, they explain to operate on premix fuel while priming the oil system.