New Crab Caps - Issue

PeterC

PeterC

Well-known member
Recently had a 59A high performance motor built - runs beautifully - but.........
When getting the distributor fine tuned (Pertronix guts) the new distributor caps where a disaster - it took 5-6 new caps to find one that was reasonably concentric - i.e. that the 8 contact points where evenly placed so that the rotor contact point had a gap that was reasonably even all cylinders.

We tried the repro black crab and the maroon Mallory units - we checked these against a bunch of original used caps and the used originals were by far better! So.. went with a good used unit .. Can’t believe that this is just a fluke with me... I heard that Bubba discussed this and at one point suggested machining the "too close" contacts to clear the gap up but in my mind that did not solve the problem of the other side where the contacts were too far away - i.e. too much gap! Anyone found a good source of crab caps that are more to original tolerances??:eek:

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Had the same problem,need to test fit the cap. My friend has had caps break rotors due to this problem. Just like everything else in this repro world. My best experiance has been to look for NOS.
 
dude said:
Had the same problem,need to test fit the cap. My friend has had caps break rotors due to this problem. Just like everything else in this repro world. My best experiance has been to look for NOS.
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Same thing with me - I just order mine from Bubbas and avoid the hassle....
 
PeterC said:
Got two new Mallory units from Speedway, 4-5 new black from the usual vendors - so John you think this is not an issue and just me?
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No Peter, I am not saying that. Would like to know who the "usual vendors" are for the 4-5 crab caps that you bought. I doubt that all of the new crab caps, that are available from our suppliers, are coming from the same manufacturing source. Would like to pin down where yours, and anyone else who is getting defective ones, are actually coming from.
 
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I agree it's frustrating that "New" parts need to be repaired before they work. That being said, I don't think the rotor/cap gap is super critical as long as there is plenty of clearance to prevent interference. Also, the rotor/cap indexing would need to be outside the width of the rotor/cap contacts to cause a problem, like maybe 1/8th inch from center. Bubba might want to address this subject regarding what the limits are.
 
I had a similar problem...the engine started crossfiring, when I took the cap off it was full of brass filings. I replaced the rotor and am still running the cap. I would like to find a better source of caps that are actually concentric.

I have some Drake caps on backorder for the Harman Collins. Has anyone had good/bad experiences with those?

Neal
 
NealinCA said:
I had a similar problem...the engine started crossfiring, when I took the cap off it was full of brass filings. I replaced the rotor and am still running the cap. I would like to find a better source of caps that are actually concentric.

I have some Drake caps on backorder for the Harman Collins. Has anyone had good/bad experiences with those?

Neal
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I have three Drake caps in service, one on a stock crab, & two on H&C's. No problems.
 
"Would like to pin down where yours, and anyone else who is getting defective ones, are actually coming from."

John - will check my bills and advise - I know the Mallory crab caps I got from from Speedway where unacceptable
 
I went through a couple of NAPA caps and rotors. I believe, some people file down the rotor but I am still confused by this since the rotor only hit one post of the cap, I would suggest a slight modification to the one post of the cap. Make sure the contact point plate is ALL THE WAY DOWN and seated properly so the retaining clip fits it it's groove and does come out. This could lead to improper path of the rotor.
 
I have read over the years about the problems with the caps. Not once have I read did you put the gasket between the cap and the distributor?.
 
I had the same problem, brass filings in the cap caused by the rotor gouging out the contacts on one side while not touching the other side. I too went through several, then when I sent my crab to Bubba he supplied a cap that seems to be perfect.
 
Would be good to hear some input on this issue from our resident distributor rebuilders. If this is a serious problem you guys must be experiencing this first hand.
 
Good post on a common problem.

Like the other have stated we would really need to know the brands that have the problem..


Heres my experience of doing a few hundred 42-48 Crab distributors in the last couple years:

Typically we use NAPA Echlin parts and have had very good performance from them.
The crab rotor from echlin is a good rotor but i dont ( thats just me) dont like the large squared off end brass tip. My fix has been to belt sand just a small amount off and round the end at the same time.
The circular clip that holds the plate in the distributor can be a problem and care must be taken to fit this clip and plate in correctly to assure the plate is square and the distributor end play is correct.

Assuming the rotor doesnt have physical contact with the terminal , its more than likely working just fine, even if off a few thousandths here and there.
Using a scope to check this terminal voltage may show a few hundred volts off from terminal to terminal but when the ignition coil has a reserve of 20,000 to 30,000 volts it doesnt matter.
Kinda like winning the lottery for 45 million and the taxes was 1000 , who would really care....:eek::D

The napa FA65 and FA64 is the correct part for these cars (excluding the Harmon Collins nose cap needed for additional clearance)
 
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