Rat-a-tat-Dat's '79 720 rebirthing of 'Helios'

[Rat-a-tat-Dat]

I finally had time to remove the engine and tear it down.

Checked and recorded all the necessary items for referral and came across a couple of interesting things.

One, looks like the main journal readings are not the same or for that matter even close to the book. According to the 'Haynes' specifications for an L20B it varies between 2.1631" to 2.1636". My measurement reveals a 2.368" micrometer reading. Can someone check this out for me please, and confirm what should be correct, thanks.

Two, the connecting rod journal diameter should be (Haynes) 1.9670" to 1.9675" and I come up with 1.9647" so does this means it's been already machined? 

As for the block, the cylinder bores are 3.346" across the board, top to bottom with maybe a 0.001" variance.

Piston ring grooves check out with no signs of fatigue anywhere. The thrust sides have minimal wear and wrist pins are pristine.

Appreciate any feed back, thanks.

[Rat-a-tat-Dat]

Here's a twist in the panties with Datsun/Nissan transitioning back in the day.

My very first post indicated that I had a 1979/1980 vehicle.  Ever since then identifying parts, especially when the appropriate year mattered, became contentious.

Another example of that fact is the Haynes manual I possess does in fact cover 1980 thru 1997 pick-ups and pathfinders. Unfortunately, those specs are exclusive for the engine. The memory forgets these small details and neglects to focus on the obvious. Hence, a search for the proper year of corresponding text and specifications are necessary for my dilemma.

It pays to have a little foresight and in doing so I had managed to acquire a 'Chilton's' repair and tune up guide a while ago when purchasing other needed parts ( let's just say my library is a little messy, lol ).This book covers 1970 thru 1984 US and Canadian models of L16, L18, L20B, Z22, Z24 and SD22 & SD25 engines. So, with that, I'm definitely on the right path and will knowingly focus on these earlier engine criteria's when ordering replacement parts.

 

It still need the experience of anyone who can verify if the con rod diameter requires standard or oversized bearings.

Appreciate you all, thanks.

 

[Crashtd420]

On 3/8/2024 at 6:16 PM, Rat-a-tat-Dat said:

I finally had time to remove the engine and tear it down.

Checked and recorded all the necessary items for referral and came across a couple of interesting things.

One, looks like the main journal readings are not the same or for that matter even close to the book. According to the 'Haynes' specifications for an L20B it varies between 2.1631" to 2.1636". My measurement reveals a 2.368" micrometer reading. Can someone check this out for me please, and confirm what should be correct, thanks.

Two, the connecting rod journal diameter should be (Haynes) 1.9670" to 1.9675" and I come up with 1.9647" so does this means it's been already machined? 

As for the block, the cylinder bores are 3.346" across the board, top to bottom with maybe a 0.001" variance.

Piston ring grooves check out with no signs of fatigue anywhere. The thrust sides have minimal wear and wrist pins are pristine.

Appreciate any feed back, thanks.

I think the info is for the L20a.... 

L20a main bearing... 2.1631-2.1636

 

L20b main bearing... 2.3600-2.3604

.0013-.0032 clearance....

 

Rod journals on both are 1.967-1.9675...

.001-.0026 clearance

 

Edited March 10 by Crashtd420

[Crashtd420]

I can't help but think your micrometers might be a little off....

Do have anything to double check the measurements or the micrometers?

 

I think oversize bearing come in .010 increments or something like that... 

[Rat-a-tat-Dat]

Double checked the measurements with another micrometer and found the first instrument readings were out. Thanks!

All parameters are within rated specifications. No need for machining or boring. Phew!

Now to order the standard replacement parts. Although if I do order, tell them it's for an L20B and everything will be fine?

Grateful for your knowledge.