340 Engine issues

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Robin House

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Hi guys, I just recently rebuild my engine. I had an over heating issue that I think I resolved with a new distributor with vacuum advance. When I take the car out for a drive, she seems to be running great but as soon as I go over 30 miles the engine shakes valiantly. I was thinking timing but if I adjust the timing any lower the heating issue returns. Right now its set to 12 initial, and advances to 28 with vacuum. Balancer was replaced last year with a summit OEM replacement (PB1004N). I used it on the engine last year before the rebuild and was fine. Only difference now is the aluminum heads. I should also mention that my compression is pretty high for daily driver, 11.1-1. I have 87 octane in the car right now but will be pulling it out today and topping up with 91 Octane. Any suggestions???
 
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In addition to the above:

If this is a 360, did you add the weight to the damper?

Is this happening with wide open throttle or with light cruise or moderate acceleration?

Can you please list these parts inside the engine: Pistons, heads, head gasket, cam shaft. The objective is to see if you really have that high static CR level, and to see if your DCR is high. Also, to check on engine balance issues.

What fuel are your running? OH, I see the info in your post... 87 is gonna be a detonation source with that compression level unless the cam is reeeeeealy biiiig. (Unless you are about the best tuner in the galaxy!) Even 91 is going to be a challenge.

You are missing one part of the equation in the total distributor advance. There are 3 parts:
- Initial
- Vacuum (which you have)
- Mechanical which is internal and separate from the vacuum advance.

With all 3 going on, your total advance at 2500-3000 RPM and above is likely in the 40's or even 50's range at light to moderate cruise. So that is the reason for the question above about when this happens.

The concern is clear: With that level of static CR, too much ignition advance is possibly going to cause detonation and that may be your violent shaking. Did you have the vibration before you put in the vacuum advance?

As for the heat, if you have higher compression, the combustion temperatures are considerably higher and that will often mean you need a bigger cooling system capacity. The AL heads are making it even worse. So while you may be 'patching' up the heat issue with more ignition advance, it is not likely really solving the prime heat issue.
 
nm9stheham said:
In addition to the above:

If this is a 360, did you add the weight to the damper?

Is this happening with wide open throttle or with light cruise or moderate acceleration?

Can you please list these parts inside the engine: Pistons, heads, head gasket, cam shaft. The objective is to see if you really have that high static CR level, and to see if your DCR is high. Also, to check on engine balance issues.

What fuel are your running? OH, I see the info in your post... 87 is gonna be a detonation source with that compression level unless the cam is reeeeeealy biiiig. (Unless you are about the best tuner in the galaxy!) Even 91 is going to be a challenge.

You are missing one part of the equation in the total distributor advance. There are 3 parts:
- Initial
- Vacuum (which you have)
- Mechanical which is internal and separate from the vacuum advance.

With all 3 going on, your total advance at 2500-3000 RPM and above is likely in the 40's or even 50's range at light to moderate cruise. So that is the reason for the question above about when this happens.

The concern is clear: With that level of static CR, too much ignition advance is possibly going to cause detonation and that may be your violent shaking. Did you have the vibration before you put in the vacuum advance?

As for the heat, if you have higher compression, the combustion temperatures are considerably higher and that will often mean you need a bigger cooling system capacity. The AL heads are making it even worse. So while you may be 'patching' up the heat issue with more ignition advance, it is not likely really solving the prime heat issue.
Click to expand...
he's absolutely right. We need a lot more info to make some good suggestions on where to look.
 
Hi guys, heres the info for the engine. Hope I covered it all.

• Not sure if the Convertor is weighted, it’s the stock convertor.
• Timing:
• Initial – 12
• Vacuum- 28
• Mechanical – 30
• Crank is steel and was balanced
• Cam is a CompCam’s x-treme energy. Lift .462 intake & .470 Exhaust with 262 duration intake and 270 exhaust.
• Pistons are Keith Black .20 pistons with Eagle “I” Beam connectors.
• Lifters are adjustable
• Block was zero decked
• Intake is a LD 340
• Carb is 600 Holly

Has for the cooling system I put in a new 3 core rad from Griffen with a 3600cfm elec fan
 
Does it vibrate sitting still when you rev it up? Does the Summit balancer have a counter weight? Some have a weight that cam be removed so they work with a 340 or 360. The converter is stock, but for what?
 
There is conflicting info..... being a steel crank seems to mean an early internal balance crank, but the converter would not have a balance weight meant for external balance. It would commonly have a small weight to make the converter neutral balanced, but we can really say from the info. OP, was the crank balanced with the converter and damper being given to the shop? Is is the original crank and do you know the engine's year of manufacture?
It would certainly need to be balanced with the light pistons and rods. Good that was done. Being that it was balanced, I'd have to assume that it was done right.

So on to the timing. On 87 octane, and with the initial and mechanical timing being so high that would be a recipe for detontation. But the 30 degrees mechanical seems way out of line. OP, is the 30 degrees the TOTAL of initial + mechanical?

Good on the rad. No way to know if the fan is doing the proper job; all depends on the setup and how that particular fan reacts to the rad and any shrouds.

OP, this vibration started with a change from iron head to AL heads? Edelbrock heads?
 
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Some KB pistons are listed as +6.0cc flat top which is 'out of the hole', just as early 340's. With block zero decked, are your aluminum heads full diameter chambered, like stock head? or or small chambered, like many aftermarket heads. Could have insufficient piston to head clearance!

At 11:1, 87 octane is a no-no.
 
You still didn't say what the lifters are hyd, or solid. you say lifters are adjustable? what does that mean?
Runs great cold after 30 miles it starts shaking, this tells me that the exhaust valves are growing and now are being held open by the lash being to tight. If they are solid lifters. If they are hyd and the push rods are to long? It wont be balance, it would do it all the time, timing? I doubt it.
 
Robin House said:
• Initial – 12
• Vacuum- 28
• Mechanical – 30
Click to expand...

Those timing figures are AFU

What would be "more reasonable" is

Initial 15
Mechanical advance measured at the crank 20

So 15+20 =

That would give you 35 under power

Then ?? 10-15 vacuum maybe as much as 20

would give you an absolute maximum of 35 +20=55 under light throttle cruise
 
ok so I"m going to try to answer the questions as best I can. this engine was build the year before I pick up the car and I ran it for the first summer. had no power and over heated but ran. it eventually cooked the rings so tore down the engine and rebuild. I had the block checked and I rebuild using the same parts except for the new rings and aluminum heads. Chamber size on the heads are 63-65, so close to stock. So the balancing it don't think would be the problem seeing it all ran fine together last year. (converter, balancer & crank)
Filters are Hydraulic Flat Tappet .
Also just to clarify it shakes when if accelerate above 30mph, not after traveling 30 mil. so in other words as soon as the engine goes under load.
 
The head chamber size sounds like Edelbrocks. That chamber size is 8-10 cc's smaller than stock so the static CR will be way up.

Robin, did the higher octane do anything to help? Or is the problem the same?
 
nm9stheham said:
The head chamber size sounds like Edelbrocks. That chamber size is 8-10 cc's smaller than stock so the static CR will be way up.

Robin, did the higher octane do anything to help? Or is the problem the same?
Click to expand...
may well be multiple issues. I agree he may have borderline compression issues. Try a compression test, to see what kind of cranking compression we're talking about.
But I still think the rotor is pointing to the wrong dist cap terminal, especially under heavy advance situations.
 
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