The fourth try...
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Junior User
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The fourth try...
I recently had the 390 rebuilt in my '74 Hiboy and its back in the shop for the fourth time in less than 500 miles. Mechanically, I've replaced everything but tranny and t-case.
1. We can't get it timed right, builder says carb's too small and he's retarded the timing to 6 degrees in order to stop the pinging.
2. We're chasing leaks: valve covers, rear main and other miscellaneous places.
3. Surging vibration whether on the road, or parked at any RPM. If I've checked tires, drive lines, etc., is there something these rigs are prone to that I'm missing? It does get worse over 55 mph.
I'm not a pro, are things like this common even when parts are new?
1. We can't get it timed right, builder says carb's too small and he's retarded the timing to 6 degrees in order to stop the pinging.
2. We're chasing leaks: valve covers, rear main and other miscellaneous places.
3. Surging vibration whether on the road, or parked at any RPM. If I've checked tires, drive lines, etc., is there something these rigs are prone to that I'm missing? It does get worse over 55 mph.
I'm not a pro, are things like this common even when parts are new?
Hotshot
Joined: Aug 2006
Posts: 10,764
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I recently had the 390 rebuilt in my '74 Hiboy and its back in the shop for the fourth time in less than 500 miles. Mechanically, I've replaced everything but tranny and t-case.
1. We can't get it timed right, builder says carb's too small and he's retarded the timing to 6 degrees in order to stop the pinging.
1. We can't get it timed right, builder says carb's too small and he's retarded the timing to 6 degrees in order to stop the pinging.
Harmonic balancer ?...
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No, it had a 360. The engine builder claimed he balanced everything in the rotating assembly.
As for the timing, it has a mild cam and 10:1 compression. The builder says it should go at a minimum of 10 degrees. He think 600 cfm carb is insufficient and is contributing to the problem.
As for the timing, it has a mild cam and 10:1 compression. The builder says it should go at a minimum of 10 degrees. He think 600 cfm carb is insufficient and is contributing to the problem.
Post Fiend
Joined: Sep 2006
Posts: 14,325
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From: Island Southeast Alaska
Carb is just fine. It's what I got on my Uni and it has no problems at all. If ya got that many leaks and other things wrong ya need the builder to give yer money back and go find an FE guy. It's just an engine and not that complicated.
Post Fiend
Joined: Jan 2006
Posts: 5,037
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From: Kasson, Minnesota
What kind of fuel are you running? With 10:1 it's very possible you need at least 92 Octane or even higher with your setup. Are you running aluminum heads?
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Post Fiend
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Sounds to me like the 'Builder" has no idea of what he is doing. I have built or helped build somewhere around 150 different engines in my 43 years of life and i have never had one that leaked as bad as what you say is happening. Also that 600 cfm carb is plenty for that engine. The other thing that you need to think of is with a 10 : 1 compression in that engine you should no be running the lowest grade gasoline, it should be mid grade or premium in order to keep you from having pinging.
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Junior User
Joined: Aug 2010
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I wiped everthing down when I shut the truck down and the flywheel cover became wet within second and began dripping. I thought it was rear main?
What you mentioned earlier is my question, how many chances do you give a builder or a motor before you just start over? Getting money back sometimes is difficult...
What you mentioned earlier is my question, how many chances do you give a builder or a motor before you just start over? Getting money back sometimes is difficult...
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Junior User
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I've only run 92 or better for fuel. Heads are stock other than the hardened stuff and beefier springs.
Sorry, I can't get cam specs 'til tomorrow. From what I understand, it's only suppose to be one step up from stock.
Sorry, I can't get cam specs 'til tomorrow. From what I understand, it's only suppose to be one step up from stock.
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My concern is the root cause is whatever the vibration is. It feels like something in the motor (maybe the cause of the rear main leak?).
The transfer case makes a little noise, could some bearing slop contribute to the road vibration?
The transfer case makes a little noise, could some bearing slop contribute to the road vibration?