Crank cutting into #3 main bearing

[fj20spl311]

That bearing comes in oversize thrust. Oversize thrust bearing are thicker on one side as the wear is usually on the clutch side.
An other option is to weld up the crank and cut it back to standard thrust. King bearing lists main bearing with oversize thrust.
You need to search by Nissan / U20

[greydog]

Man of man...I continue to learn a lot here.
Nothing like going to school on Greg's dime.....

Dan

[JT68]

What I meant to say was it varies by bearing brand. Some .010 under size bearings have an oversized thrust, some have a standard size thrust, so you need to give the actual bearing you will use to the crank grinder with the crank to size to that bearing. Same thing with .020 - you don't want them to "guess" at the size and have an overly tight or sloppy fit. Been there before...

[Gregs672000]

Thanks for all the advice! I was not sure what and when to order for bearings, as I do not know if he will have to go down a size now since that journal is compromised or not. I will discuss that with him and once determined will find the right sizes and give them to him for final specs. Thanks again.

[JT68]

If you have to go past .010, I'd suggest you find aother crank or have yours nitrided since I know you will run it hard. .020 is through the factory nitriding. J

[GeoffM]

Greg, in that article , it mentions that the SBC guys chamfer one of the parting shoulders of the main bearing. It provides a oil channel connection between the oil ring groove on the main journal and the thrust bearing/crank gap. This seems pretty like a good idea on the face of it (HA!) but not sure about unintended consequences. You may want to talk to your motor guy about his thoughts on it.

[Geistfahrar]

Wow! This discussion re crank end-play, clutch free-travel and trans main-shaft play got me scratching my head, as to whether I might have goofed on my engine/trans rebuild in 1983. With 107,125 on the odometer at teardown, the synchros were getting flakey, so I decided to re-build ( as necessary ) the trans, as well as the engine. Thinking back 35 years, I can't be sure of all the details. The receipts/invoices for the 80's were stored in my tool shed, which he rats found over time and shredded.

Since the timing train & cover were shredded, & the valves bent, I completely stripped the block, except for the crank, which I checked with a plastigauge for journal wear. As the journals wre within tolerance, I did not opt to grind the crank. The pistons were sent out for magnefluxing ( due to valve contact ) & though they checked ok, I decided to have the cylinders rebored to 0.020 oversize. The camshaft miked ok so I kept the old one. The bottom of the head was not flat, so I decided to have the machine shop deck it.

The head & block were sent to a "now defunct" machine shop in Vernon CA, for boring, milling & re-fitting of all parts except the timing train, which I installed when I got the engine back. As the shop had a good reputation, I did not check the engine for crank end-play or "restored" journal clearance.
I did check the head on a granite block for surface flatness, but not total head depth. I now believe a "fair amount" of surface was removed, as I am getting chain rattle with a dry start-up. I finished the re-build with new OEM timing parts.

I stripped the 5-speed completely, & replaced some ( but not all ) bearings & gears. I replaced all synchro rings, brake-bands & blocks, according to the service manual instructions, as well as main & counter-shaft shims ( re formula on pages 128/129 ). All parts were Nissan OEM from Sun Datsun ( Whittier CA). I replaced the clutch disk, pressure-plate & throwout bearing, & after mateing with the engine & installing in the car, I adjusted the free-travel of the clutch pedal.

My reason for "fretting" about screwing-up, is that after putting 25,574 miles on the re-build, my 1st gear synchro is showing enough sign of wear, that I have to "double clutch" ( or rpm match ) to down-shift quickly. Virtually NO city ( stop-light ) or stop-n-go driving ( mostly open highway betwwn SGV & Mammoth Lakes CA ). So Why the difference between the 1st set ( 100K+ ) and the current set ( 25K+). Any ideas?

Garry S

[fj20spl311]

Its very rare that a transmission rebuild will bring your transmission back to new specs.
There are parts like the slider that are very expensive and serviceable usually at the first rebuild.

[Geistfahrar]

Yeah Phil, especially now that the 5th gear synchro part are no longer available. I am not really concerned about the condition of the trans itself, as I only drove the roadster around easy suburban streets, since I stopped taking it up to Mammoth ( 2001 ). I was more concerned that I might have put the wrong sized shim on the main-shaft, & caused excessive end-play.

I don't think I have the same problem as Greg, since I always check the bottom of my oil-drain pan after a change, to see if any strange material came out with the oil.

BTW, regarding 5-speed sychro parts, are the ones Dean ( and others ) still selling from Nissan's remaining stock, or has Nissan's supplier re-started the line for all except the 5th gear?

Here is one of the synchro parts invoices that the rats didn't destroy. 32364-20100 is the 5th gear slider.

001.jpg

download/file.php?mode=view&id=39728

Garry S

[Gregs672000]

What gear oil are you running? My trans temp dropped significantly going from Valvoline to Swepco... the stick no longer got hot. Not sure what effect it may have on sycros, but I won't run any other oil in my box. Still, how often are you finding it necessary to downshift into 1st! I could probably make mine do it, but I always double clutch and rev-match, which I'm sure would be required for a smooth shift with my box... it's just part of the dance now, and I have a hard time not doing it in every car I drive.

Regarding metal flakes in the oil, they were not visible on an oil change, and were probably mostly filtered out by the filter. I only found very small shavings by dropping the pan. Not to worry you, just sayin.

[Geistfahrar]

greg, I am a chronic "worrywart", because at my age, my memory is pretty flakey, and since the tool-shed rats destroyed my roadster records from the 80's, I don't know if I have replaced the oil pump on the car. The service manual "end view" of the assembled U20 engine, shows the pump directing the oil from the pan into the filter, before getting back into any moving parts. I would think that any material small ( light weight ) enough to be picked up by the pump would be caught in the filter, and the big stuff ( shaved metal, dropped washers etc. ) would remain in the oil pan when the liquid is poured-off ( re-cycled ).

Your opinion -- am I on or off-base here?

Garry s

[fj20spl311]

The filter is a By-Pass design, therefore once the pressure difference between the inlet and outlet reach the relief pressure, the oil and grit flows through the filter without going through the filter element. You are correct that big chunks stay in the pan.

[Geistfahrar]

Thanks for the heads-up Phil, I didn't know the pump had a relief valve. I thumbed through my service manual, and found p.46 free of the smudges & oil stains on most pages, so I concluded that I hadn't serviced/replaced the pump. I know that I pulled the dizzy & fuel pump in 82', as I had to replace the broken jackshaft ( see attached invoice copy ). I replaced the fuel pump on the 90's, but that did not involve any other moving parts.

Looking at the text & tables on p.46, it appears that the pump should can reach the relief valve release pressure at "modest" rpm's when the engine is "cold" ( below thermostat opening temp ). What was Nissan's reason for by-passing the filter under those conditions? It would appear that the only way to determine that the valve is opening, is to put a stethoscope against the oil filter feed line and "race" a cold engine!! But can't tiny particles in the oil scour a cold engine as well as a warm one? posting.php?f=3&t=31051&mode=reply&d=1351#

Jackshaft invoice.jpg

Garry S

[Gregs672000]

Wanted to finalize what I am 95% confident was the reason for my thrust bearing failure. On the damaged crank, I noted that the pilot bushing was pushed much further in than the roller bearing in my new crank. Today I put the backing plate on the trans and pushed the crank onto the input shaft of the trans until it lined up as if it were in the engine. The shaft bearly hit the pilot bushing, and I'm confident that it caused the crank to be pushed forward instead of guiding and aligning. Over time it ate the thrust. Everything else looks great. Just waiting on the new crank being ground, block bored, valve reliefs cut, and assembly.

[C.Costine]

Wanted to finalize what I am 95% confident was the reason for my thrust bearing failure. On the damaged crank, I noted that the pilot bushing was pushed much further in than the roller bearing in my new crank. Today I put the backing plate on the trans and pushed the crank onto the input shaft of the trans until it lined up as if it were in the engine. The shaft bearly hit the pilot bushing, and I'm confident that it caused the crank to be pushed forward instead of guiding and aligning. Over time it ate the thrust. Everything else looks great. Just waiting on the new crank being ground, block bored, valve reliefs cut, and assembly.

I am not picturing this, are you saying that the input shaft was pushing on the pilot bering instead of slipping inside of it?