Datsun Roadster Forum-311s.org

They were two different part numbers.

david premo wrote: ↑Thu Feb 13, 2020 3:08 pm They were two different part numbers.

But not on the sprocket.

If you buy it new it comes in a box with a part number on it.

david premo wrote: ↑Thu Feb 13, 2020 3:31 pm If you buy it new it comes in a box with a part number on it.

If only the previous owner had bothered with that....

Absolutely agree that mixing up the gears themselves would not be a "basic mistake." Who would know?! I was referring to a good race engine building shop (which this was) missing how important it is to make sure they confirmed cam timing! That's what has always bothered me. One combination may be more obviously worse than another in how it runs on the street. Curtis, what was your combo? Metric cam with SAE crank or the opposit? Just curious...

SAE cam sprocket with metric cam. Crank gears are the same.

All I can tell you is it was a major PITA to chase down when you don't know.

So you basically have to have a known metric cam sprocket , put it on top of a unknown cam sprocket and if they match perfect , it is metric? But the difference is very close between SAE and metric...That is how I am understanding it
Saw the Tech Wiki write up and it explained things well...
Linda

Linda wrote: ↑Fri Feb 14, 2020 3:59 pm So you basically have to have a known metric cam sprocket , put it on top of a unknown cam sprocket and if they match perfect , it is metric? But the difference is very close between SAE and metric...That is how I am understanding it
Linda

Yes, very close but just enough to make the engine run like crap. I stood them up on the teeth and lined them up to the side against a wood block. It was very clear the slight difference. A little fussy to make sure they are square and sitting firmly on two teeth.

Since the metric sprockets are most common, the typical error is metric sprocket on english cam. If you re-use your old early sprockets and accidentally use a metric cam, the opposite can occur.

How bad it is also depends on the cam grind naturally. The stock grind is short duration, so 6 degrees of error is way off the mark. Either all the valve events are way early or way late.

A longer duration cam would be potentially more forgiving, because the valve events are by definition starting earlier and ending later. Still, if the lobe position followed the factory specs, it would still be significantly off its potential max power.

A high lift, long duration cam has the most likelihood of valve-piston collision with this error. This setup is probably the least forgiving. A mis-timed and overcammed engine will be the soggiest of all performance wise, so that is something to avoid. A properly timed engine with a moderate cam will run better every time.

No matter what, if the wrong sprockets are used, the engine will be way off on power and torque, might run hot (temp) too depending. Every cycle of the 4 is affected negatively.

The net effect is similar to retarding the ignition timing 8 or 10 degrees. May idle ok, but will never be making optimal power since all the valve timing is wrong. Will always feel like the carbs or distributor is maladjusted- That is because all the valve events are happening at the wrong time.

Wow, so it's not just gears? The SAE and metric cams are ground differently eh? Sounds like the only way you would know (unless there are clear marks on the gears and cam) would be to go through the process of actually checking cam timing on the assembled engine. And unless the gear was adjustable (which I've not heard of for an R) the technician would be wondering why it's always off 6 degrees!

Gregs672000 wrote: ↑Sat Feb 15, 2020 12:51 pm Wow, so it's not just gears? The SAE and metric cams are ground differently eh? Sounds like the only way you would know (unless there are clear marks on the gears and cam) would be to go through the process of actually checking cam timing on the assembled engine. And unless the gear was adjustable (which I've not heard of for an R) the technician would be wondering why it's always off 6 degrees!

The cams are easy to check with the cam bolt. The SAE bolt will go in to the metric cam and wiggle around. The metric bolt will not go in an SAE cam. Of course that is predicated on you having both bolts.

Gregs672000 wrote: ↑Sat Feb 15, 2020 12:51 pm Wow, so it's not just gears? The SAE and metric cams are ground differently eh? Sounds like the only way you would know (unless there are clear marks on the gears and cam) would be to go through the process of actually checking cam timing on the assembled engine.

Correct. The cams also two different part numbers, and correct, it isn't just the bolt that is different. The profiles are pretty similar. The lobe position relative to the keyway is different naturally. If Nissan had not done that, the sprockets would be identical other than a 5/32 vs. 4 mm (.0013" diff). Nissan tried to keep everything separate with the engine number delineation and the different part numbers. Pretty sure Nissan's intent was reduced emissions since all this coincides pretty closely with the addition of the smog gear.

Well the fun with this never ends. Dave F. came over today so we could verify his 1500 cam gear is SAE. So we proceed to check against all the cam gears I have including ones I thought were SAE. His gear was a half tooth out from all the gears I have including a new gear. Now I'm wondering and finding out all my gears are metric.

So in frustration I pull the front off the 3 main engine that came out of my stroker. Sure enough it is SAE, lines up perfectly with his gear. Later I decide to check the cam in said engine. The SAE cam bolt will go in to a metric cam and is very loose. A metric cam bolt will not go in to a SAE cam. So what do I find out? The engine has a metric cam which explains why the engine never had much power. Sigh.

I believe the cam I just had ground is a SAE cam, but it is at the machine shop. The question now is did they grind it to the SAE profile or the metric one? I'll have to call Monday.

Oh and they had a SAE bolt in the metric cam. I don't know why it didn't come apart.

All I can say is "ugh Charlie Brown...". Well, at least you KNOW now and can fix it instead of having given up, never solving the mystery.