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US Model 1975 Midget 1500 Cam Specs Needed

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datsun_medic

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I just checked the cam timing on my 1500. From what scarce info I've found online it's suppose to be 18:58, 58:18. Of course I don't know what those numbers are referenced to so it does me no good.

I've measured at the lifter 12:19, 54:29 @ 0.050. The intake centerline measures where the calculations put it but the exhaust centerline is off about 20 degrees (I could have made an error measuring with it being 3:30AM).

Is the exhause lobe assymetrical on these engines to compensate for the crappy exhause port?

If I base the centerlines off the calculations then my cam is advanced 4 degrees, which might be better with these numbers on the low-rpm torquey 1500.

The wear on the cam seems negligible and I'm getting 0.243 lift off the intake lobe. I haven't checked the exhause lobe yet. Next day off though.

Does anyone know the cam timings @ 0.050 on the lifter?
 
Hello and welcome to the Forum.!

Have you seen This page ? From what i have learned here on this forum is that the cam specs were modified for smog.

mark
 
Your right it is not , but it does give you some other figures for comparison. i should have posted this link Black art of cam timing . This helped me immensly when i timed my engine from scratch. i did the wheel about 97 times and then thought about it for two weeks before i bolted the covers up....Runs great....Whewww
i have a chiltons here that lists the specs.

it says for the '75 ..intake opens 18 BTDC no info on the exhaust.


Black art of cam timing 2



hope this is at least of some help.

mark
 
The link helped. I rechecked the timing this afternoon making sure I got TDC right on by making a positive stop tool by tapping threads in a hollowed out spark plug and running a long threaded bolt (with the tip rounded) through it.

I got a similar valve timing which still has an absolutely huge exhaust duration. Perhaps with it being a 30 year old car someone has done something crazy in its past. The lift comes out at the correct value so I don't think it's worn.

I'll keep messing with it. Thanks for the help.
 
Ok. I realized trying to get the cam to lift significantly at 18 BTDC was futile because my centerlines were not at an even split if I did it that way. So I redegreed the cam using the centerline angle method and here are the new readings:

All taken at the cam...

0.010 16:59, 58:20
0.020 6:49, 47:7
0.030 1:43, 42:0
0.040 -3:39, 38:-5
0.050 -7:36, 35:-10

Centerline angles are ~112 for both intake and exhaust. Lobe separation at 110. Definitely a torque cam.

This gives a nice even split. So either factory cam patterns are established at 0.010 cam lift or it's a little worn, but even. I can live with that for the time being. I appreciate the ideas and support.
 
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