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My 620 build thread.


J's 620

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Today I actually noticed some smokiness coming out of the tail pipe after I had the plug wires sorted out. Couldn’t tell if it was white or blue. This was on a little throttle up while working the carb. I have lost coolant from my overflow bottle, but it was the cap that was leaking. Right now the radiator is up to the neck and I haven’t been adding coolant. 

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I would never run a synthetic oil in an older Datsun. You will never ever get to the point where you might need the extreme protection afforded by it. Waste of money. In addition synthetic tends to seep past old seals and gaskets where regular oils do not. I will say that today's commercial oils have about half the zinc  ZDDP anti scuff additive than the oils that were around when your Datsun was new. Today's engines use roller cams instead of flat tappet cams and don't need it and it's bad for the latest catalytic converters so it is being phased out. Oil producers claim that the old levels were excessively high anyway and the new oils are reverse compatible. I'm not taking a chance with my valuable valve train. So I run a diesel oil like Shell Rotella T4. Have run 15w40 in the past and am now using 10w30. Diesel oils are slightly more detergent so they will darken quicker when you switch because it's cleaning your engine.

 

For now anything out the tailpipe could be the cylinder cleaning itself.

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I used to run the 15-40 rotella. So switch back to it? What 10-30 are you using?

 I was thinking a synthetic would be good ONLY because I had to drive the truck through the winter.
 I see the seepage though and I agree with you on it getting past seals. New seals even. 
 What’s your opinion on that FR3 friction additive? Hot shots brand maybe?? Snake oil? It’s like $20 for a little bottle and way thin. The zddp replacement (not the Lucas brand) additive is also very thin and very expensive. Also snake oil? 

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So here’s what I did. I adjusted the valve lash, they were a bit tight. Like .006” and .008” tight. My fault for not checking after machine shop work. Changed plugs, put my ngk wire set back on and took the autozone brand wires back. It runs like it should. No shakes, completely still. 
 I bought some 10-40 stp dino oil and a mobil filter and I’ll have to change that tonight after work. 
mike that plug suggestion was spot on even though they were all extremely dirty. 
 Hainz the wire pulling was a good method of troubleshooting. 
 Thanks to both of you for suggesting the valve lash adjustment. I think that’s what it really needed. (Besides a change of oil)

 mike I just realized you said 10-30 is what you use not 10-40. I’m assuming your using the rotella 10-30 diesel oil. It gets up to 90 here in east Idaho during the summer so I think a 10w-40 would be better than a 30. I guess I’ll look at a chart. I can always pick up some rotella and use what I bought for a different vehicle.

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I’m worried about the smoke from the exhaust. It seems pretty pronounced today. It doesn’t smell sweet. I’m not sure what it smells like really. It just smells burnt. 

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I just changed my oil yesterday. I went from a 10w-40 full synthetic to 10w-40 dino oil if you will. I’m hoping it’s still cleaning itself out but it’s never smoked as long as I’ve had it. 

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First off, great work on the truck J.  It’s great to see more 620s in the PNW.

 

The alternator issue I’ve seen before using Chinese, Thai, and Taiwanese made parts. The “accepted tolerances” they use in Quality Assurance are well outside the OE manufacturers tolerances. They’ll use what amounts to watered down metals and make the parts as small as possible.  This lead to my old job making it a fireable offense to bring any part from those countries onto the job site.  Right down to the nuts, bolts, and washers. 
 

The lack of copper in your parts is what causes them to break and fail.  To avoid boring you to death with metallurgy I’ll use an analogy most Ratsun members will get:

 

If you break a water hose there’s a magic amount of duct tape to get you home.  

 

If you put a roll of duct tape on it, you’re probably fine until you get paid on Friday to get a new hose.  This represents a good US, Japan, German, Swiss, and some other countries quality made alternator.  

 

If you just place a small piece you’ll stop the leak until you turn the key and have the thermostat open. Then you gotta keep applying new tape. Maybe you’ve seen this with the ‘lifetime warranty’ one year alternators. 

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2 minutes ago, Soundline said:

First off, great work on the truck J.  It’s great to see more 620s in the PNW.

 

The alternator issue I’ve seen before using Chinese, Thai, and Taiwanese made parts. The “accepted tolerances” they use in Quality Assurance are well outside the OE manufacturers tolerances. They’ll use what amounts to watered down metals and make the parts as small as possible.  This lead to my old job making it a fireable offense to bring any part from those countries onto the job site.  Right down to the nuts, bolts, and washers. 
 

The lack of copper in your parts is what causes them to break and fail.  To avoid boring you to death with metallurgy I’ll use an analogy most Ratsun members will get:

 

If you break a water hose there’s a magic amount of duct tape to get you home.  

 

If you put a roll of duct tape on it, you’re probably fine until you get paid on Friday to get a new hose.  This represents a good US, Japan, German, Swiss, and some other countries quality made alternator.  

 

If you just place a small piece you’ll stop the leak until you turn the key and have the thermostat open. Then you gotta keep applying new tape. Maybe you’ve seen this with the ‘lifetime warranty’ one year alternators. 

Yes all too often, it’s why I try to get them rebuilt. Too bad the guy I went to cracked the alternators front cover getting the bearing out. Fricken brute. 

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1 hour ago, J's 620 said:

Yes all too often, it’s why I try to get them rebuilt. Too bad the guy I went to cracked the alternators front cover getting the bearing out. Fricken brute. 


There’s a fine art to re-wrapping an alternator.  I did one in my technical school back in the day... that used all US made and sourced materials.  Building it with a machinist friend was fun and we got something that was very high quality.  
 

I only rarely touch this stuff now. I did a bathroom exhaust fan a couple years ago, a complete copy/paste of the original design made in Oct 54’.  I’d expect that fan to work until about 2082.

 

Does make me curious about building one for my L20b.  A ‘nuclear grade’ alternator.  Might be an interesting side project.

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Yeah, casting some of the components to get the right resistance and metal mixture.  You gotta keep the wire warm so it doesn’t crack.  Then you dip it for the coating you need.  
 

That’s a rebuild.  It’ll last as long as the original Japanese built ones. If things are made properly then you can use them for decades.  I wish REAL manufacturers existed in the secondary market.

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On 3/29/2021 at 9:28 PM, J's 620 said:

I used to run the 15-40 rotella. So switch back to it? What 10-30 are you using?

 I was thinking a synthetic would be good ONLY because I had to drive the truck through the winter.
 I see the seepage though and I agree with you on it getting past seals. New seals even. 
 What’s your opinion on that FR3 friction additive? Hot shots brand maybe?? Snake oil? It’s like $20 for a little bottle and way thin. The zddp replacement (not the Lucas brand) additive is also very thin and very expensive. Also snake oil? 

 

On 3/30/2021 at 10:09 AM, J's 620 said:

Based on temps on the chart I’d probably be ok doin a 5-30 or 10-30 in the winter if I’m driving the truck and a 10-40 or 15-40 for summer. 

 

10w30 Rotella T4. I think 15w40 a little thick for my usage.

 

I would never uses anything 5w. Oil is selected based on the maximum temperature expected till the next oil change. If not above 50F then you could use 5w but if not going below 0 F much 10w30 will do and you can run to over 100F on it.

 

I run exclusively in the summer and temps well below 100F

 

Friction additive....

 

Well it assumes the engine oil is somehow deficient and that the owner is somehow needing more protection than he really needs... as in if some is good more is better. ALL oils are certified to minimum standards of protection including the $1.99 WallMart "jug 'o oil" though I wouldn't use it. Name brands have better anti foaming, and corrosion inhibitors  and detergent packages. More protection than you need. Additives are basically snake oil, not that they don't work, more like you just don't need them. 

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On 3/29/2021 at 10:20 PM, datzenmike said:

ZDDP anti scuff additive than the oils that were around when your Datsun was new

The oil that HD and BMW sell are also high in ZDDP so that is another option. BMW bikes were oil cooled therefore the need for ZDDP, unsure why the HD runs higher ZDDP, but the HD oil is a bit less $ than the BMW oil

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ZDDP has little to do with cooling. It's a zinc anti scuff additive package primarily for non roller flat tappet cams. Pretty much any older push rod engine will need it. Today's cars do not and the zinc is bad for the newer catalytic converters. The ZDDP level has dropped to at least half what it used to be 40 years ago.

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My truck still has the CA cat converter and it’s only a few years old so I don’t really use the zddp nor do I use those expensive additives, anymore anyway. 
 

 I got a good look at the puff of smoke from the exhaust, it is a bluish tint so I’d guess that was oil. It’s not a massive puff but more like the thickness of water vapor in the morning cold. I also think it has a black tint in there as well so I’ve been trying to dial in the carb slowly. 
 

on a separate issue, anybody with one of these trucks ever see water come in where the speakers would be? I can’t quite narrow down where it would come from. It pools up in that little pocket when it really rains. I’ll have to use the garden hose and troubleshoot? 

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On 4/6/2021 at 5:05 AM, J's 620 said:

My truck still has the CA cat converter and it’s only a few years old so I don’t really use the zddp nor do I use those expensive additives, anymore anyway. 
 

 I got a good look at the puff of smoke from the exhaust, it is a bluish tint so I’d guess that was oil. It’s not a massive puff but more like the thickness of water vapor in the morning cold. I also think it has a black tint in there as well so I’ve been trying to dial in the carb slowly. 
 

on a separate issue, anybody with one of these trucks ever see water come in where the speakers would be? I can’t quite narrow down where it would come from. It pools up in that little pocket when it really rains. I’ll have to use the garden hose and troubleshoot? 

on the passenger side? check the antenna mount/gasket

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Did you recently rebuild the engine? They will puff a bit of blue until they are broke in. 

 

There are body seams under the cowl and fender that let water into the cab. No seam sealer back then. 

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On 4/9/2021 at 9:04 AM, ]2eDeYe said:

Did you recently rebuild the engine? They will puff a bit of blue until they are broke in. 

 

There are body seams under the cowl and fender that let water into the cab. No seam sealer back then. 

I haven’t had the motor rebuilt. I did have the cylinder head worked on months ago, the smoke started recently. I check the oil today it’s at the full mark and looks like new oil. 
 

ill check that gasket, it is mainly on the passenger side where it leaks, the driver side pocket gets very little. I’ll have to look under that cowl. 

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The plugs are fouled again. I haven’t pulled them to see how bad, but the way it runs is a sure sign. I bet it’s oil fouling again. 
Time for a rebuild maybe? I could only guess that oil is getting past the rings?? It’s cylinder #3 again that’s the worst. 

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Synthetic oil will go places that 'normal' oil won't. Might take more than a few weeks to flush it out.  

 

Easy enough to do a compression test and record the number then squirt a couple of teaspoonfuls of engine oil in the plug hole and retest. Above 150 would be nice on a hot engine. If the numbers go up significantly with added oil, then the rings are worn including the oil control. If compression is good that would tend to point to the intake valve seals.

 

To foul the plugs would take a lot of oil burning. Have to ask how often you have to add oil by mileage??? Does it puff blue on cold starts? This would indicate valve seals.

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