So I've been playing around with timing and figured I'de start from the
basics, with finding TDC on the pulley (since it doesn't have a mark for it).
So I tried the procedure on this link: http://www.teamfc3s.org/info/article...fying.html#TDC
but my "TDC" is about 20 deg off (retarded) from where it would be
according to the procedure. Has anybody tried the above and gotten
correct results?

-Henrik

 

What your problem is, is that at some time, someone has put a 12A pulley on you 13B engine.

I read your post a couple of days ago and thought I'd give the article a try on a 87 non turbo engine thats been sitting in my garage for a couple of years now.

I did the method described in the aritcle and when I got through I said *this method is not accurate at all*. It was as you described in your post.

So I went to the shed and got out a old pulley from my spares. I tried it on that same engine and wo and behold the TDC was within 5degrees of the LEAD mark.

What happened is that I've owned and torn down 12a engines in the past. When I rebuilt the subject 13B some years ago, I must have mixed the 13B and 12A pulleys.

I suggest borrowing someone elses pulley from his car and comparing it with yours.

 

cool info - so just, so I understand completely, you got the procedure
in the article to give correct results (within the 5 deg) when using a
13b pulley on a 13b block (duh!) and same results as I posted if you used
a 12a pulley on the same 13b block? I have got to check this now, the
previous owner had the engine apart at Mazda (they dropped a pintle
cap into it when servicing the injectors) re-re to get it out, so it could have
been swapped at that time.

Anybody know how to indentify 12a vs 13b pulleys (before I run off to
the junkers with my camera...)? I presume its just the pulley, not the
hub as well?

-Henrik

 

******** so I understand completely, you got the procedure
in the article to give correct results (within the 5 deg) when using a
13b pulley on a 13b block (duh!) and same results as I posted if you used
a 12a pulley on the same 13b block? ***********************

Exactly. I also had trouble with this particular engine when installing the cas. It was always cocked to the far left or fwd position to get the timing marks aligned. It was not like that prior to me rebuilding it and I always wondered just WHY?

I read your post and thought I'd try that with this engine since its on the garage floor and easy to get at. I came up with a measurement for TDC that was about the same distance from the LEAD mark as there is distance b/t the LEAD and TRAIL marks and maybe a touch more. So I considered the method in the article bogus.

Then out of the blue I decided to try another pulley. Got one from the shed and installed it and did the procedure again. WHOA! The new mark was approx 5 degrees from the LEAD mark.

Oh. At some time I got smart and held both pulleys against each other. Yes. The marks were not in the same place.

From there I figured out what I'd done. I'd put a old 12A pulley on after the rebuild (at least five years ago). Easy to do since I've rebuilt about three 12a in the past.

Later I went to the first generation site and did a search on timing. I found a post that described what happens if you use a 13B pulley on a 12A. You might look at the first generation post over the last three days and see it.

I know of NO way to id the pulleys. They all look the same to me. Yes. Just the pulleys, not the hub.

P.S. TDC for the front rotor should have the keyway for the e-shaft at the nine o'clock position. But its not worth pulling the front bolt and hub off. At least not for me.

 

This is the post in the first generation I referred to: https://www.rx7club.com/forum/showthread.php?t=419935

Look for my post at the bottom and in it I refer to one of the other posts on that thread. The fellow (Wackyracer), who wrote the post I refer to knows up from down, it seems.

 

Compare a 12A CARB engine with a 13B. It's the fixed pointer on the 12A that is located further to the left of the eccentric shaft than the 13B. It's noticable.

 

Please ignoret the post about the first gen pointer vs the 13B. I eyeballed that but went back later and I'm not sure about that anymore. I need to measure to make sure about the pointers location being different.

There must be a better way of finding TDC. What about locating an apex seal in the LEAD sparkplug hole. Then adjusting the cas til one of the small teeth align perfectly with the reluctor. Then turning the eccentric shaft til the next apex seal arrives. Then count how many small teeth on the cas have passed from one point to the other. TDC would be inbetween or half the number of teeth that have passed. So you'd turn the eccentric shaft to that inbetween point and there lies TDC????

I still think your problem is he pulley. Borrow one and see.

 

So I had a look at my pulley, I can't see the keyway but if I draw a
line through two of the bolt holes, it will pass almost exactly between
the lead/trail timing marks. So, since the hubs are the same, can you
have a look at your two pulleys - which one has two bolt holes lining
up between the lead/trail timing marks? (the 15* offset should be easy
enough to see visually.

-Henrik

 

This is the best write up I've found for finding TDC and will work with any pulley http://members.optusnet.com.au/~onec...-%20part%20one

 

Thank you. I'm going to try that. Since I wrote above, I found three pulleys laying about in the shed. I'm sure they are all second generation like my car. Two out of three have the marks different. Off by approx five to ten degrees. The mounting holes (4) all have the same pattern, so it's not like I'm confused about how to mount a pulley.

I used the timing method mention at the very beginning of this thread. The sparkplug hole method. I find that is only ball park accurate. So I got pissed. I took my spare engine and layed it on its side, sparkplug holes up. I found TDC using the sparkplug hole method to get inside the ballpark.

Then I got my oil squirt can out and filled the front rotor thru the Lead/Trail sparkplug holes. I then rotated the flywheel back and forth watching the oil level rise/fall. At it's peak I noted where the one of the 24cas teeth was at that time. Then I repeated rocking the flywheel back and forth and making the same notation of where the singel cas tooth was. Bottom line is I could repeat again and again that same place. I called that TDC and marked the pulley.

Since I now have read YOUR new url, I'm going to try that method. I've always been aware of the eccentric shaft keyway slot being 90 degrees over to the exaust side but never considered that an accurate way to determine TDC, UNTIL I read your url and the mention of the two pulley attach bolts being inline with the fixed pointer. Now that means something, and I'll try the url you posted.

 

Glad that I could help.