Datsun Roadster Forum-311s.org

Greetings all, I've been reassembling the bottom end on the U20. Yesterday I got to where I was installing the rods back onto the pistons and wanted to make sure I oriented them correctly. The manual is terrible in its drawing of the oil passage on the rod for the oil hole that squirts onto the cylinder wall to lubricate the rings, and there is no mention whatsoever of orienting the rods in the narrative. I looked around the internet and even called "tech support" (a knowledgeable Roadster friend who happened to be at the Shedd BBQ) and even that extended brain trust was unsure (I don't know if the amount of beer n burgers had anything to do with it...). Anyway, I remembered I had a manual I recently acquired for a 620 PU, and inside they depict the rod mounted on a piston in the correct orientation for an L-series. While the actual location of the hole is slightly different vs an R or U motor, they are all clearly biased toward one side.

Based on this, I "determined" (unless some very knowledgeable person posts otherwise!) that the hole goes to the RIGHT side of the engine and faces forward (right side being from sitting in the seat) and the numbers stamped on the rod to the left. So, when you're assembling the pistons onto the rods, the numbers will face you and the oil hole faces forward. I took a pic of an old rod showing the numbers and the circled oil hole. With the front of the engine to the left you would assemble the rod onto the piston like this. I 1) hope this is correct and 2) that this helps someone else to eliminate any confusion or concerns!

The bearing tangs are on the same side as the main cap tangs when installed correctly.

While it is not the definitive answer, my understanding is the oil hole is to spray oil on the side of the cylinder that gets the side thrust from the cylinder firing which I think is the left side. I can check my manuals when I get time, probably tonight.

Peace,
Pat

david premo wrote: ↑Mon Aug 23, 2021 10:40 am The bearing tangs are on the same side as the main cap tangs when installed correctly.

Good to know. In this case I only had the rods out so I couldn't look.

Habitat.pat wrote: ↑Mon Aug 23, 2021 11:01 am While it is not the definitive answer, my understanding is the oil hole is to spray oil on the side of the cylinder that gets the side thrust from the cylinder firing which I think is the left side. I can check my manuals when I get time, probably tonight.

Peace,
Pat

Yep, that's what Dave F reported too...

The leaking rod bearings sling oil to the cyl walls
( But maybe not with that new fangled scraper thing)
You need a spray to hit the Piston center bottom to cool it thoughand lube the wrist pin

They point to the camshaft/jackshaft.

What Mike said. Toward the jackshaft.

Greg,
Your original question has been expertly answered by the experts, but a pic to print and put inside the factory manual in the "rebuilding" section might be useful for newbys (which we all were at one time, right?). And, you are correct: the factory manual does not answer your question specifically.

The Chilton's '61-'72 Guide does say, "On P, L16, L24 and A12 engines, the oil hole at the bottom of the connecting rod must face to the right side." (p.48) Okay, so we could insert (excuse the pun) the U20 in that list. That agrees with the previous answers from the experts, and places the conrod numbers on the left side.

Reckon that may be standard practice across the industry, just to keep things simple? Well, the second photo shows that is NOT the case, with the U20 assembly alongside a Volvo B30.

Hope everything is going well with the rebuild, and it's a given that you are attentive to every detail.

Jon

All perfect answers. Another way. Quick glance, there is a part number for the rod on the beam of the rod always on the same side and on one side only. Part number on the connecting rod ending in 25540 faces the front of the block.

Dean

I seem to have a set of the same pistons/rods as shown in this post. I got them several years ago from a friend and now we can't figure out if they are special or not. Mine have cross hatching on the skirts. Is there anything special about this particular rod/piston or is it just a standard replacement??

You can have any piston knurled to take up slop - to much clearance
It's not a ideal solution but works , kind of a in car overhaul trick

Bwana wrote: ↑Fri Feb 09, 2024 7:23 pm I seem to have a set of the same pistons/rods as shown in this post. I got them several years ago from a friend and now we can't figure out if they are special or not. Mine have cross hatching on the skirts. Is there anything special about this particular rod/piston or is it just a standard replacement??

I am by no means an expert on engine internals, but it looks like that piston may have been dropped or something ... looks like a large burr on the bottom of the skirt.

There’s also what looks like a crack between the oil control and second compression ring. The entire cast piston looks rough. Just my 2 cents

I think redroadster is correct... knurled piston.