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M72 assessment


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The forks were pretty filthy and full of gunked up old oil. No liquid oil left. I sprayed everything with degreaser and washed it in a bucket of soap and water.

here's the end bushing.

there's the seal..

 

I primed the lower clamp while i was at it. Semigloss black tomorrow.

 

 

Hopefully I can get it all back together!

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  • 7 months later...

 

 

 

 

 

 

Next I sat my rear bearing in the carrier. It was very loose, so I used some Loctite bearing retainer. Of course afterwards i saw online that the bearing is supposed to have some slip for expansion. Too late now. Hopefully it'll be OK.

 

I noticed a weird thing at the front bearing carrier- there seemed to be an oil passage hole through the carrier that deadended at the case. It seemed like it should have led to the tube that traverses the length of the motor, under the crank. I probed with a drill bit, but didn't find a passage so I just went ahead and put in the bearing. We'll see there, too.

The tube going from the back to the front of the engine is the oil feed line. In the front, the oil goes up through a vertical oil passage and out through the tiny hole you have pictured and because it can't go anywhere else (it can't go through the bearing outer wall, right??) it will flow through the rounded opening you see in the picture and feed the front oil slinger (lubricating right side connecting rod).

Same thing happens at the rear of the engine for the left side connecting rod. Sometimes using mismatched parts and not verifying if the hole in the rear bearing carrier alligns to the oil passage in the engine case (thicker gasekets...) can lead to oil starvation of the left side rod.

 

 

The pipe going from the front to the rear of the engine case sometimes ROTATES and the front passage gets closed (at the front the pipe is not straight cut) . Make sure the pipe did not rotate and is in the right position. Compressed air while engine case is empty might be usefull. Secure the oil pipe with a proper fixing bolt inserted from the bottom of the case (oil pan off). Throw away the OEM fixing bolt and calculate the apropriate length for the one who WILL do the job. Probably 1-2mm longer will be ok.

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Thanks Valicaddy! I think it's oiling OK. I'll double check that pipe next time she's opened up.

 

Here's the bike solo, a couple weeks ago. Haven't got the car on yet. Needs a lot of work too, and I ran out of steam...

 

 

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Nice!

 

How many miles since rebuild?

Part code for Nissan pistons (who made them)?

Issues?

 

Silv-0-lite 1-9079

http://www.kb-silvol...etails&S_id=363

Hastings rings, can't put my hands on the receipt just now.

 

(I should note that my machine shop skimmed the back of the head to maintain the same combustion chamber volume. Because although you have tighter fit in the bore with these pistons, the distance from gudgeon pin to crown of piston is less, so without skimming the head you would have a tiny bit less compression. ScooterBob who recommended these pistons didn't bother with his own bike- the machine shop thought it was a good idea.)

 

I didn't track the odometer, so not sure, but it only has about 12 hours riding.

It took quite a bit of fiddling to get the foot shifter working well. Just a tiny turn of the adjuster bolts makes a difference.

It turns out the crank was twisted during my rebuild, but I didn't know enough to recognize that. I had it straightened and it was running great, but last time I rode it it made suspicious noises and so now it's in the shed until I have a whole weekend to see to her. Owning a roached M72 will teach one patience and tenacity!

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WOW ! After seeing the condition of your engine I have some hope for mine. The timing gear seems like a good place to look next, was removing the front cover much of an issue ? Bruce

 

Nope, take the front timing cover off, pull the points plate/distributor. You'll see the screws for the timing gear cover. Might take a whack with a mallet.

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