Datsun Roadster Forum-311s.org

Thanks!

The plot thickens.

I wasn't sure what I did with the cam bolt for my S.A.E. engine. While cleaning in the garage I found a cam bolt in a box. Checked the threads on it and it is 3/8-16. I get the cam from the engine and it goes right in. Tried the 10mm and it won't go in. Found a second cam bolt and it too is 3/8 and in it went.

So it appears I have a early cam with a metric gear. Have to wonder how that engine ran.

That makes me worried as to what is in my stroker. The cam that came out which I checked today is metric. The cam I put in was a performance cam I got and I believe I used the same cam bolt. I didn't change the gears as they were in good shape. BUT, now it is causing me doubt and makes me wonder if the problem I'm having with engine not running good in the mid range is a result of some mixed parts?

I think I'll pull the engine this Fall or Winter and check stuff and get a new rear main seal put in.

Went to Steve's this morning and we compared the S.A.E. sprocket. You can clearly see the tooth off just a little from the metric.

Bingo. If you need an early (for the 3/8 threaded cam) sprocket, I have some. As I said in the previous thread, if you mix up the sprockets, that 3-3.5ish cam degrees error is 6-7 crank degrees. That is a whole lot of cam timing error. It will run, but not well. J

JT68 wrote: ↑Sun Jul 21, 2019 3:46 pm Bingo. If you need an early (for the 3/8 threaded cam) sprocket, I have some. As I said in the previous thread, if you mix up the sprockets, that 3-3.5ish cam degrees error is 6-7 crank degrees. That is a whole lot of cam timing error. It will run, but not well. J

Thanks, Steve let me get a set from him. I got a heater core from him as well.

So what does the off timing make the engine run like?

Curtis wrote: ↑Sun Jul 21, 2019 5:04 pm

JT68 wrote: ↑Sun Jul 21, 2019 3:46 pm Bingo. If you need an early (for the 3/8 threaded cam) sprocket, I have some. As I said in the previous thread, if you mix up the sprockets, that 3-3.5ish cam degrees error is 6-7 crank degrees. That is a whole lot of cam timing error. It will run, but not well. J

Thanks, Steve let me get a set from him. I got a heater core from him as well.

So what does the off timing make the engine run like?

Assuming a stock cam and no valve/piston collisions, just about any poor running situation you can think of because ALL the valve events are out of sync with the crank and pistons.

At a minimum, it will never feel "right" or want to rev well. If you measure it with a dyno, you'll be well off the factory torque curve at most if not all rpms. Sluggish and mis-tuned.

The exact symptoms depend on what parts were swapped and whether the cam is badly advanced or retarded. If advanced it may idle fine, but be struggling at rpm. If too far retarded will have lousy low end, poor mid range and still underpowered in the top end.

Depending on CR and cam grind it may behave like the ignition timing is too retarded and may also run hot. Lots of possibilities, but lots of variables too, so a myriad of effects. In short nothing good.

Not trying to steal anyone's thunder here but Dave Premo brought this issue to my attention when we were building my stroker motor for my 66. Dave and Stan figured this issue out years ago when they were building a stroker for Stan. So, at least a little credit is due Stan and Dave. On my three main early motor as I said I ended up going with a later metric cam and a Japanese aftermarket metric timing gear. I had not run into this issue with the first stroker I built as it was a later 5 main motor that already had the metric cam. At any rate it is good info for sure.


Steve

Not trying to steal thunder but many people don't know this and I'm not sure this is in the wiki.

I think we should put a full write up about it in the wiki. Or did I miss it? Not something you might think to go looking for. On the other hand if you're shopping for parts the roadster vendors make a point of it.

However if one does a search on here to buy parts and goes straight to the forklift parts they can end up with a problem they didn't know about such as my engine by a PO. I have a feeling because of when this car was done in probably the 90's that they got the cam gear from either the dealer or a parts store.

Agreed. I will get the info in the wiki as it is not there. Thanks.

Steve

Do you want me to take some better pictures to use?

Sure, if you want to. That would be great. Thanks.

S

Here is the write-up. Anything I missed let me know. If you have better pics I will add them. Thanks.

Cam Sprocket SAE vs. Metric


Steve

S Allen wrote: ↑Tue Jul 23, 2019 8:37 am Here is the write-up. Anything I missed let me know. If you have better pics I will add them. Thanks.

Cam Sprocket SAE vs. Metric


Steve

That does the job, thanks.

Nice write-up. Thanks Steve,Curtis, Dave & Stan

Thank you JT for your in depth comments.

S