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Rough idle problems
#1
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tsherry
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Just got the '37 top end put back together. Replaced the valves with correct originals; repaired the very worn tappet screws to a correct shape; reassembly went fine (after a second head gasket--first had a defect that caused a huge leak).

Got her running again last weekend, had decent compression but not stellar (85-90, which is up from 0 on the low to 90 on the high due to valve problems). Idled roughly last weekend as the valves were adjusted cold at that point, but ran it long enough to retorque the head, then back at it yesterday.

Ran her enough to heat it up enough to adjust the valves hot; an adventure of course--I did not do them while running. Still runs rougher than it should but smoother than before. Valves obviously have just a bit more work as there was a tiny bit of gauge movement on the vacuum gauge, but it was steady centered on 18PSI with about 0.25/0.5PSI flutter. The vac gauge was connected to the manifold connection for the wipers.

There does not appear to be a vacuum leak; I did plug the port to the distributor, which does leak when connected normally.

Plugs, points, cap, rotor are new; wires are newer aftermarket, and a timing light shows all are firing. It does for the life of me feel like a cylinder's not firing, but all plugs are heating up as they should (hand held thermal sensor) and the manifolds are heating up evenly.

I'm wondering if I'm chasing my tail with a bad timing chain....Any thoughts?

Posted on: 2/7 20:46
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Re: Rough idle problems
#2
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Chuck McDonald
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A couple of years ago my 37 120 had the same issue "Slightly rough idle" I drove the car to Ross Miller who adjusted the valves while the engine was running and he did find a couple out of adjustment. After the adjustment the cars engine was smooth as silk!. Ross did mention that the correct way to adjust the valves accurately was to have the car running. Most likely that will solve you problem.

Posted on: 2/8 3:15
Chuck McDonald
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Re: Rough idle problems
#3
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jwblazek
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How's the bushing in the distributor, worn? Vacuum advance plate free and not bouncing back and forth? My 39 had rough idle, found two things, bushing in distributor was shot and someone had removed the vacuum diaphragm
advance spring which allowed the breaker plate to wobble

Posted on: 2/17 12:02
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Re: Rough idle problems
#4
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tsherry
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Hadn't thought to look at those but will definitely do so now!

Been too cold to do anything out in the garage even with the heat on. Maybe this weekend.

Posted on: 2/17 21:07
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Re: Rough idle problems
#5
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tsherry
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Vacuum advance is certainly inoperative. Hooked it up to a hand vacuum pump and it would not hold vacuum. So, it looks like I'll be replacing that....

Any recommendations on replacement parts? (Autolite distributor)

Posted on: 2/18 23:57
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Re: Rough idle problems
#6
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tsherry
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Here's the advance unit--this looks different--as does the distributor than the illustrations in the parts manual.

Attach file:



jpg  20210218_211812.jpg (216.02 KB)
3448_602f4dfacb9dc.jpg 1920X1440 px

jpg  20210218_211930.jpg (509.62 KB)
3448_602f4e0d1dfd9.jpg 1920X2560 px

Posted on: 2/19 0:35
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Re: Rough idle problems
#7
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Joe Santana
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Sorry to divert this thread for a personal message. I can’t make the PM function work for me to ask Chuck McDonald if he has a local resource to change oil and lube and check fluid levels in the drive train.

Posted on: 2/19 4:51
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Re: Rough idle problems - solved
#8
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tsherry
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A few valves were just a scosh out of tolerance; ran her hot, re-adjusted, smooth idle. Not quite smooth enough to balance a nickel but substantially better than it was a couple of weeks ago. Engine vacuum holding rock steady at 19psig.

Next up, fixing a tiny little fuel leak from a fuel line fitting.

RE: the vacuum advance, ordered one off of ebay, should be here next week.

Posted on: 2/20 15:31
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Re: Rough idle problems
#9
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Joe Santana
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Chuck,
The PM to you isn’t working for me. Could you try to PM me or post a recommendation for a shop/station near Rockville for oil change/lube services?
Thanks, Joe joes@mktx.com

Posted on: 2/21 12:03
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