Datsun Roadster Forum-311s.org

Unklpat, I don't disagree at all with your post above, but he jumped right in so here we are! At least he's not wasting any Time!

Well I have some good news and bad news. I was able to get the head off (end of good news). It looks like the pistons might have some issues. Also, when pulling the crank pulley off I noticed some play from front to back on on the crank (see video).
https://www.youtube.com/watch?v=VDt10JoDu0k

Almost forgot! With the timing cover off I was able to take a look at the gears and chain. I have not yet fished around in the oil pan for the part of the timing chain.

People watch the video of the crankshaft moving back and forth! The most common cause is people that keep the clutch depressed waiting for the light to change. All crankshafts have thrust bearings to keep the crank from moving forward and backwards while loads are applied to the end of the crankshaft. End play on the crankshaft should be between.002-.007 in, and not greater than.012 in. So why does this happen? It’s pretty simple, you have the clutch depressed and all the spring force of the clutch cover is pushing the crankshaft towards the front of the car. The bearing has a film of oil that gets swept away after a few seconds of continuous pressure. Without the lubricant of oil it wears out the thrust bearing and crankshaft thrust journal. In the video you can see how much it’s moving is so far out of specification that the only thing to do is pull the crankshaft out and replace it or have it repaired. When we were replacing clutches on cars that had them in 70’s and 80’s we would check end play every time we did a clutch job.
Dave

Dave, this is one of the best explanations of this phenomenon I have ever read. Thanks!

Thanks David

Holy crap, the thrust surface is gone on that one....BTW the other thing that kills the thrust surface is failure to maintain clutch free play. As the clutch disc wears, the clutch fingers move rearward (towards the throw-out bearing). Ultimately, if not corrected, that will eliminate all free play and then the clutch plate will constantly load the thrust surface pushing the crank forward-usually resulting in crankshaft death.

the lesson is everytime you are under the car, check your clutch freeplay.

Ugh, that crank shaft movement sucks. So sorry man. Mine ate the crank hugely from a cockeyed pilot bushing in the flywheel end of the crank and I had to replace the crank. We won't know how bad yours is until you remove the crank and inspect the bearings.

Regarding the rest, the engine was running very rich so you have a lot of carbon build up on both the head and the tops of the pistons. Otherwise there's nothing concerning that I see. The pistons will clean up, then they will need to be inspecyed, measured for size, ring lands measured, inspect the cylinder bores for major scratches, measure the cylinder and see if we can hone it for new rings or if it must be bored for the next size piston and purchase new pistons and rings. The gears didn't look as bad as I thought they might. You could probably reuse the large jackshaft gear, but the rest have enough wear and some marks that would lead me to replace. Others opinions welcome!

The head needs to be disassembled to inspect the valves, seats and guides. I saw this on Amazon, and it has both the compressor as well as the suction cup dowels you would use to lap the valves. When/if you get to this point we will tell you what to look for and how to do it.
https://www.amazon.com/Mardatt-Compress ... ljaz10cnVl

So, no easy or inexpensive fixes here. That crank issue really sucks. But, the reality is it would not have lived much longer... question is, now what? Rebuild? Replace with a good used and less expensive (?) R16? Engine swap? No easy answers here... and if you're looking into parts you're starting to see what kind of $$ just parts let alone machine work/access may run. We have all been here, so we can help guide.

Sorry for duplicate post, not sure how that happened!

Just curious could you show a pic of that worn thrust bearing down under? Never seen that kinda wear.

Dean at Datsun parts sells bearings with oversize thrust surfaces. You should plan on a full rebuild, and depending on your machine shops, a long wait for service. Do everything you can to bring this motor to factory condition. You will then have 8 or 10 years before you have to touch it. Pat

unklpat wrote: ↑Tue Apr 18, 2023 1:33 pm Dean at Datsun parts sells bearings with oversize thrust surfaces. You should plan on a full rebuild, and depending on your machine shops, a long wait for service. Do everything you can to bring this motor to factory condition. You will then have 8 or 10 years before you have to touch it. Pat

Ya, I just wonder what the crank itself looks like... mine was trashed and would have required welding etc.

Thanks for all the responses! At this point I am still dismantling the engine, I was able to get most of the exterior components off. Once I figure out what new parts I would need to get, and how much $$$$ I'll decide which route to take. I am heavily leaning to rebuild the motor. Below is a few pictures of the timing gears from what I was able to pull off last night. I also noticed on the chain guide that one of the bolt heads was completely toast! Luckily once the bracket was removed I was able to unscrew the bolt by hand!

nismou20 wrote: ↑Tue Apr 18, 2023 12:40 pm Just curious could you show a pic of that worn thrust bearing down under? Never seen that kinda wear.

Sure thing, I have not removed the crank yet but I did take a video of the front/back movement when I flipped the motor over.

https://www.youtube.com/shorts/cyA6T5RiVcw

Wow! Never seen a crank move like that. I have replaced the clutch on all my roadster but never checked the crank movement. DOH! Something new to think about and wonder....

I Will certainly check the free play on all the cars this week. Never want this to happen to my cranks. I almost always shift out of gear at red lights except on hills...

Thanks Dave and JT