Datsun Roadster Forum-311s.org

Time for me to revisit this subject.

So while my car is down for rust repairs I pulled the engine so I can address a couple things. One being the suspicion that I have a mixed cam and gear on there. So I pulled the pan and timing cover. Pulled the cam gear and checked the cam and found it to be metric. Now the fun and confusion begins.

I have on hand 5 cam gears as shown in the photo. From left to right:
#1 Gear from a metric motor I bought more than 10 years ago from a car being parted out to make in to a stroker. It was rusty and crusty like the motor and I believe original to the motor. Has a number 1 cast on it.
#2 A new gear for an H20.
#3 Gear from the 67 car I am restoring. Cam is SAE and I suspect the gear is metric. Has a number 2 cast on it.
#4 The gear from my stroker that I'm having problems with in the mid range RPM. Has a number 2 cast on it. I suspect it is SAE, more on this later.
#5 A used SAE gear I got from Steve here in our area. Has a number 2 cast on it.


I bought some 5/32 and 4 mm key stock. Previously we put the gears on a round shaft screwdriver. I checked the key stock on two metric and one SAE cam with dial calipers and they were all 0.15". I put what I believe is a metric gear and the SAE gears on all 3 cams and no play side to side.

Next I lined all the gears up back to front in the same order to check them on both sizes of key stock. See next post.

Checked the timing mark on all the gears and they're all the same place. Photo of the gears on the 5/32 key stock. The teeth all line up.
Next pushed the gears at the bottom from side to side counter clockwise. The two at the bottom of the photo, #4 and #5 swing a little more. Clockwise they swing even more. Not sure why since they're tight on the camshaft.

They do the same thing with the 4mm key stock.


So anyone have any ideas because I'm not seeing how else they differ?

This isn't a great way to compare them, because on that small of a diameter, the change in linear measurement is minimal. In radial measurement diameter doesn't matter, 3 degrees is 3 degrees. A probe with DRO can easily pick it up though.

In the last photo, Going from the rusty gear forward, the rusty gear being #1, 1,2,3 are the same. #4 (shiny gear) has the teeth a few degrees clockwise. 5 looks back counter clockwise, but harder for me to tell in the photo.

The difference is visually subtle, but 3 degrees of cam timing is 6 crank degrees and that is a mile. More than enough to make an engine run like crap if 6 degrees out of time.

Unless forced, filed or damaged, a 5/32 keyway will be quite tight on a 4mm key, so that may be a clue. 4mm is .001ish larger.

I have both style gears available if needed. J

As they say, you run what you brung. Unfortunately I don't have the necessary setup to do this the way I want.

I thought what if I set them on the teeth and square them up at a right angle. Sure enough you can see a slight difference in the two bottom gears from the top two metric. One the known SAE gear and the other that was unfortunately in my stroker on the metric cam.

Maybe not as scientific as I would like but you can see it. Next stop, install my new metric set I have.

What about a machinist? Doesn’t a machine shop have the tools to assess something like this?
Linda

There's nothing to assess. Pair a metric cam with a metric sprocket and the engine will be happy. Pair an SAE cam with a SAE sprocket and same thing goes. Mix them up and you will wish you didn't.

We have correct sprockets available for both.

J

JT68 wrote: Tue Feb 11, 2020 7:27 pm There's nothing to assess. Pair a metric cam with a metric sprocket and the engine will be happy. Pair an SAE cam with a SAE sprocket and same thing goes. Mix them up and you will wish you didn't.

We have correct sprockets available for both.

J

There is when you buy an engine with wrong damn gear in it! Sins of previous owners and I was the victim since I did not know about the difference. I had never owned a 5 main before the stroker and had no reason to even know about the difference. As long as this thread saves someone else I'm happy about it.

Thankfully you and others helped me learn about it. I hate metric even though it makes more sense.

Is this documented in the wiki? Do the numbers mentioned mean anything?

Curtis wrote: Tue Feb 11, 2020 11:01 pm

JT68 wrote: Tue Feb 11, 2020 7:27 pm There's nothing to assess. Pair a metric cam with a metric sprocket and the engine will be happy. Pair an SAE cam with a SAE sprocket and same thing goes. Mix them up and you will wish you didn't.

We have correct sprockets available for both.

J

There is when you buy an engine with wrong damn gear in it! Sins of previous owners and I was the victim since I did not know about the difference. I had never owned a 5 main before the stroker and had no reason to even know about the difference. As long as this thread saves someone else I'm happy about it.

Thankfully you and others helped me learn about it. I hate metric even though it makes more sense.

You are right about that! (PO error) I think several folks have made that mistake over the years. It only becomes obvious when you start checking valve timing events with a degree wheel. Maybe that is what Linda was asking? Novice builders and most shops never go to this level of assembly detail. It takes hours. - when you do, and the sprockets are mixed up, it becomes very apparent there is a major problem. Otherwise, the symptom is it will never run quite right.

So JT, what's the ultimate effect of the cam/crank timing change with incorrectly matched gears? Does it advance or retard the cam? I worked on a race car that refused to rev and would eventually overheat where we concluded the engine builder (a very reputable shop in Seattle) had installed the cam one tooth off, but now I wonder if maybe they were using mixed gears. That makes more sense to me than a shop making such a basic gear install mistake.

In my case the cars runs and revs. But the mid range is where the problem is. It would flutter and flatten out. If I pull the choke out and richen it then it runs better and and starts to rev back up.

So with one type mismatch its 6 degrees advanced, the opposite mismatch is 6 degrees retard, so depends on which combination. Unless using some radical cam or a severely cut head and decked block there is little chance of a valve collision, but just like Curtis described, it will run, it will just never run right, its just way out of time/tune. But it's not really a basic mistake, if you don't know about the issue, you would never see the issue by looking at the sprockets.

1/3 of a tooth would be hard to see, but I don’t get how there isn’t some way to measure them, with a digital caliper or something to tell them apart? Like if you measured everything, isn’t there one value that would be consistently different on a metric sprocket, as an example?
Linda

Gee, a part number on the damn sprocket would have been nice. Datsun, love em and hate em.