Datsun Roadster Forum-311s.org

So, I'm not new to Roadsters, having owned a 1600 for 44 years, but I acquired a couple of 2000's just a couple of years ago. One of them sheared the jackshaft woodruff keys and left me stranded, last fall. I'm just getting around to really investigate and repair; what I found were severely scored cam bearings in the caps & towers. The camshaft itself was relatively unscathed. I have replaced the cam towers and caps from a spare U20 I have and after quite a bit of work, have managed to align all the towers, so that the cam turns freely, (with no rockers in place)

I made the assumption that the oil pump was the culprit and I have acquired a new one from Dean, but when I tried to prime the pump with an electric drill turning CCW, I am not seeing any oil come out of the camshaft oil holes. I did check the cam when I had it out and all the oil passages where clear, so I am guessing I have a blockage in an oil passage, in the block or head that is causing a lack of oil to the top end?

Not sure where to go next. Is there a single oil passage responsible for getting oil to the head? Is there something else I'm missing?

MY GUESS IS THE JACKSHAFT BEARING SPUN AND HOLES IS NOT ALIGNED. COULD BE WRONG AS I HAVE NOT LOOKED AT THE OIL PASSAGE DESIGN IN 20 YEARS.

SORRY FOR THE CAPS, IT MAKES IT EASIER FOR ME TO READ LOL HATE GETTING OLD

I checked the WIKI in the U-20 manual, the head is supplied through the last jackshaft bearing journal

I agree with Phil, the rear jackshaft bearing is the one that passes oil through to the top end. I bet that whoever installed it miss aligned it.

OK, thanks to you both, Phil and David. You have pointed me in the right direction. There may be a problem with the jackshaft and/or bearings. I have removed the fuel pump and distributor, base and drive gear. The jackshaft should just pull out, right? It spins ok, but it seems to be recessed into the block more than it should be and binds up as I try to pull it forward.

Sorry but you will need to pull the engine to correct this problem.

Not sure I would assume that the passage to the head was blocked, but it is possible. I would also highly doubt it was an oil pump problem (good luck returning that..)

What is more likely is that the head was messed up in the first place and that caused the camstands to self-destruct (lucky about the cam).

Before you remove the motor, before you drop the pan, remove the head (It needs to come off anyway) and spin over the engine with the starter, or remove the distributor/OPpump drive gear and spin the oil pump CCW with a drill. If the block and oil passages are ok, oil should come out of the rear galley vigorously once the block galleys are full. If that is the case, you probably don't need lower end work, it is just a cylinder head problem. best, j

So, what I've found so far is that when the woodruff keys were sheared, that allowed the jackshaft to slide rearward in relation to the gears and that caused the rear end of the jackshaft to get mangled up a little and I think it moved far enough to, at least partially, block the flow of oil to the head. It seems the jackshaft retaining plate will keep the jackshaft from moving forward, but there is no real thrust surface to keep it from moving back, if the gears move?

What I'm not sure about, yet, is what caused the woodruff keys to shear off in the first place?

A common failure is for the "nose of the jackshaft" to snap off. I would bet on lack of oil to the bearing caused the failure.

milehiroadster wrote: Sat Apr 19, 2025 12:47 pm So, what I've found so far is that when the woodruff keys were sheared, that allowed the jackshaft to slide rearward in relation to the gears and that caused the rear end of the jackshaft to get mangled up a little and I think it moved far enough to, at least partially, block the flow of oil to the head. It seems the jackshaft retaining plate will keep the jackshaft from moving forward, but there is no real thrust surface to keep it from moving back, if the gears move?

What I'm not sure about, yet, is what caused the woodruff keys to shear off in the first place?

Yikes, yes, you have an unusual failure on your hands. So, now that you know the keys are sheared, probably best to pull the engine and tear it down.
An in-car repair would be iffy at best.

The woodruff keys do not set the end play (the shaft itself, gears and the retainer plate do), so the key shear would not allow the JS to move axially. The keys only establish rotational position.

Your question is the main issue though, under normal circumstances the JS woodruff keys should never shear, so something must have siezed,jammed the JS. Sounds like a JS bearing self destructed or the JS or retainer plate had way too much wear and end-play, so the JS seized against something. A broken distributor drive gear also might jam the JS possibly. Whatever it was, you will likely find more destruction as you disassemble. If the rear JS bearing spun (certainly possible) that would also kill oil flow to the head as previously mentioned. Certainly a bummer.

If the rear journal of the JS is damaged, that rear bearing probably self-destructed. The journal surfaces typically don't damage themselves. j

Regarding the JS thrust surfaces, yes, there are four, the front face of the JS and the rear face of the smaller JS gear. both sides of the retainer plate. So the JS keys don't affect thrust position.

It is also possible that the opposite scenario occurred. If the cam seized even for an instant (due to head warp or other problems) that might shear a key too. In that case the JS and JS bearings may not be damaged.

Either way, you do need to tear it down to find the exact cause and fix it correctly. cheers, jt

JT, thanks so much for all your input on this. Your explanation of JS thrust surfaces makes perfect sense and I'm now leaning towards the jackshaft retaining gear bolt may have loosened enough to allow the JS to move to the rear and get jammed up. A PO had installed it with only a star washer, which seems to have allowed it to loosen itself.

It’s highly probable that the jackshaft bearing was improperly installed, I say this because of the failures that have occurred. The rear jackshaft bearing is how oil is delivered to the cylinder head as well as the jackshaft itself. I have attached a few pictures and added the directions for the oil flow. In the top picture you see the rear of the shaft that rides in the bearing. The wide grove is for oil delivery around the shaft. The middle picture shows the flow from the rear crankshaft bearing to the jackshaft and up to the cylinder head. The bottom photo shows the path from the main oil gallery to the crankshaft and jackshaft. If any of the oil ways are blocked major damage will occur.

Alan, This is really unfortunate. Let me send you a complimentary set of Durabond seamless jackshaft bearings. They are the best.

https://datsunparts.com/collections/eng ... t-bearings

Dean

Allen, FWIW here are some photos of the bearing and how it fits in the block. Understand, I have much more limited experience than Dave P, JT and Dean but this series of posts (I found in the tech wiki) were very helpful. Mostly credit our member Mr. Macarthy and worth seeing his website.

Thanks all, a lot of very helpful info. I luckily have an extra 2000 engine, (with a marginal head), as well as a 2000 short-block that has a freeze crack in it. I also have a borescope tool that allowed me to take a good look at the rear JS bearing and it looked pretty good. So, I took the jackshaft out of the short-block and put it in the engine. It turns very nicely by hand, so I put the oil pan back on and tried to prime the oil pump. The engine gallery's filled right up and oil came out of all the oil holes on the camshaft. So, the rear JS bearing is no longer blocked and oil is flowing well. Not sure if I'm going to attempt to fire this up or not. I know it would be a huge gamble, but it all looks and feels good, at this point.