All Small Six Trying to track down vibration between 1400 - 1600 (resolved the 1800 - 2200 RPM issue)

[awasson]

Hey gang,
I'm still fine-tuning my inline 6 to get the most out of it.

I just added some more back pressure via a new muffler. Prior to this, I have had several glass pack mufflers which were fun but kind of loud. The new system sounds amazing and quiet but a vibration that was a bit noticeable has become more noticeable. I thought it was the clutch/flywheel issue that I would resolve by replacing that with a T5 but now that the engine is quieter, I can notice it more and it happens in gear or out of gear when I just slowly rev from idle to about 2,200 RPM. It begins somewhere around 1800 RPM. After around 2200 its much smoother and not really noticeable.

A few things about the engine:
New build last summer/fall, 1966 7-mains block with about 750 miles on the engine. Crank was ground, balanced, polished. Rods sized by shop and hung on pistons. Block bored 60 over. Static compression ratio a little under 9:1. Clay Smith H-6474-0-B camshaft & Clay Smith hydraulic lifters, OEM springs, OEM valves and rockers. Degreed to match cam card within a degree. HEI ignition. Header. Weber 38/38 on small log. New PCV valve, closed circuit into a catch can and into the log below the carb.

No leaks, no blowby, no oil burning, starts easy, revs quickly, plenty of power, no back firing ever, break in was a breeze. The carburetor is a Clifford/Redline carb configured for the ford 6 200 and I have it dialled in for the best lean idle.

Some ideas:

• I can detect the vibration or shake any time I rev the engine slowly of quickly, whether it's under load or out of gear, clutch in, clutch out.
• I advanced the initial timing to about +24° and it is noticeably better but that seems like a lot of advance. My vacuum advance is +10° on ported vacuum. If I had a higher compression ratio, I'd be worried but I can't detect any detonation knocking. I will call the Clay Smith tech line tomorrow to see if they have a recommendation for initial timing and curve for that cam for my compression ratio.
• I've found that the idle jets on the 38/38 have a significant effect on just off idle response. I was running 60's for a while but thought it was too rich and recently went back to 55's. I will put the 60's back in and adjust for best lean idle and see if that improves it.
• I've read that sometimes by mistake a transmission shop will balance the flywheel like a small block ford when they surface the flywheel and that will introduce a shake that matches my description. I will be replacing the transmission with a T5 and plan on having the flywheel surfaced and checked for balance when I can find a shop to do that.

Anyway, I'm still in the investigative stages so if anyone has a similar experience, I'd be interested in hearing about it.

Cheers,
Andrew

 

[DON]

An O2 meter would rule out any carb issues. Which I don’t think you have. I think you might be on the right track with clutch/ tranny. New harmonic balancer? Maybe eyeball your accessories, bent pulley ECT. Remove extra belts, maybe even all of them for a short test?

 

[awasson]

Thanks for that advice about removing the belt. I only have an alternator (and water pump) on it but you never know. I'll remove the belt and see how it performs when it's cold since I wont have the fan and water pump going.

The damper appears to be in good shape and still laminated well with no slippage.

 

[powerband]

engine passing through a mid RPM range with a vibration can be hard to determine source. taking off the fan belt to check is a good idea. I chased down a vibration the '63 / 170 which found to be the generator's shaft in the brushes end bearing/bushing from long time sitting, had rusted on one (bottom) side which ground off into egg shaped shaft causing odd vibration when revved ...
.
be sure there are no clearance issues where engine or tranny contacts car body - exhaust headers, T5 shifter box tower , belhouse etc ..
.
200 Flywheel isn't like SBF. 250 uses same FW as V8 but not weighted (neutral balance) unlike most Ford small blocks. (some HiPo SBF V8 are unweighted/neutral lbalance) are SBF uses 28 or 50 ounce weight which would shake a 200 apart.
.

" Comes with 28oz & 50oz Bolt on external balance weights. "
from

Pardon Our Interruption...

.

have fun

 

[DON]

Same flywheel, but neutral balance, like the Balancer, ….. makes me suspicious

 

[awasson]

I'll remove the belt and test tomorrow to see if maybe the alternator, water pump or fan are doing anything weird. The alternator does vibrate with it but I thought that was a result of being at the end of the motor, like holding something in your hand and shaking your arm.

I bumped up my idle jets and it seems better, smoother at low speed and off idle but smells richer at idle. I thought the 55's were about right in terms of the smell test. With the 55's it was passable; it smelled like a car with a carb and no catalytics but not eye watering. The 60's are a bit on the rich side.

I also used a vacuum gauge to get the best vacuum on my initial timing. I took it to the best vacuum and then backed it off, just a touch. The last time I did that was with the 55 idle jets and I was close to 19 inches. I've changed a lot since then and was using a light more recently so I haven't tested vacuum for a while. With the 60's I'm getting just about 17 inches and it's pretty advanced. I'll have to put the light on it and see where it's at but It's got to be somewhere between 22° - 26°.

The timing change and jets have bumped the idle up to about 900RPM from about 600RPM. Off idle response is definitely improved. It is smoother at low speed but that vibration is still evident so if it isn't the alternator, fan or pump then it must be the flywheel. I had the crank checked for trueness before I had it ground, balanced and polished.

Thanks for all of the input.

Cheers,
Andrew

 

[B RON CO]

Hi, I can't believe that I am going to post this, because it is such a huge reach. A slim possibility could be that the input shaft is too small for the pilot bushing, or maybe the input shaft is not fully engaging the pilot bushing. I have heard of the bell housing not directly centered on the back of the block on other engines, but never heard this on our engines. I'm sure that you have both dowel pins in the block. Good luck

 

[awasson]

Hi, I can't believe that I am going to post this, because it is such a huge reach. A slim possibility could be that the input shaft is too small for the pilot bushing, or maybe the input shaft is not fully engaging the pilot bushing. I have heard of the bell housing not directly centered on the back of the block on other engines, but never heard this on our engines. I'm sure that you have both dowel pins in the block. Good luck

You may be onto something. I haven't installed the 5-speed yet and the throwout bearing on the stock 3-speed is noisy. I cleaned it and repacked it when I installed the engine and it seemed ok on inspection. The dowels are lined up and everything is snug but I was wondering if the input shaft was tweaked and had a bend it it or something.

When I remove the transmission from the bell, I'll fire it up and run it without the transmission hanging off the back to see if it still shakes.

 

[alwill923]

My guess would be the flywheel and/or clutch pressure plate. Had a similar problem with a chevy 350 back in the 70's. New car and it was the flywheel and clutch.

 

[John Ha]

Have you checked your engine and transmission mounts for goodness? I suppose they're new but even new stuff can be defective and fasteners can work loose. Also, exhaust systems have resonant frequencies and can vibrate at certain rpm ranges. It's a little hard to tell from your description how the vibration is manifesting itself but that might be another place to check. Look for hanger straps or other things that might allow small movements. Have you had another person rev it to the appropriate range while you investigate? That might be a useful thing to do.

 

[awasson]

Have you checked your engine and transmission mounts for goodness? I suppose they're new but even new stuff can be defective and fasteners can work loose. Also, exhaust systems have resonant frequencies and can vibrate at certain rpm ranges. It's a little hard to tell from your description how the vibration is manifesting itself but that might be another place to check. Look for hanger straps or other things that might allow small movements. Have you had another person rev it to the appropriate range while you investigate? That might be a useful thing to do.

Thanks John. Yes, motor mounts are good and solid. I’ve got a brand new set of motor mounts that I’ll put in, just in case. The trans mount is good too (and I have a couple of new spares of those too) but It gets a new one with the 5 speed.

Exhaust system is new front to back with all new hangers but with the old loud exhaust that I had cobbled together there was a vibration that was somewhat hidden but the drone of the old exhaust. Now that it’s quieter, the vibration is more noticeable.

I’ll get it off the ground tomorrow and pull the transmission to see if that was the cause.

 

[awasson]

My guess would be the flywheel and/or clutch pressure plate. Had a similar problem with a chevy 350 back in the 70's. New car and it was the flywheel and clutch.

I think/hope that is the issue. I’ll be able to rule it out fairly soon.

 

[awasson]

Some testing progress!

Belt on, belt off makes no difference, so I think the alternator and water pump are ok. Moving right along, I removed the transmission this evening. I’ve got the bell housing supported by a 1000lb ratchet strap and the motor mounts are new, I just replaced them.

The engine a lot smoother. A slow Rev from idle at about 700 RPM to about 3000 RPM is so much smoother. The vibration is almost entirely gone and I’ve been able to pinpoint where it started. I thought it started at 1800RPM but it actually starts at 1400 RPM and the steering wheel vibrates, you can see it oscillating. It used to go to about 2500 RPM but now it’s gone by 1600 RPM, so it’s a very narrow band that comes on like a switch at 1400 RPM and is off like a switch by 1600 RPM.

The clutch, pressure plate and flywheel are still attached so tomorrow I’ll pull the starter and clutch linkage so I can get the clutch and flywheel off. I’ll have the flywheel surfaced and then put it back together. If I have the time, I’ll put the flywheel back in without the new clutch and pressure plate and run another test. I’ll be putting in a new diaphragm type clutch and pressure plate so hopefully it will be nicely zero balanced.

I’m feeling optimistic. It revs way snappier without the 3 speed attached.

 

[drag-200stang]

If you have not already checked, make sure the the input shaft fits the crank bearing correctly.

 

[wsa111]

So it vibrates not moving & the the shifter is in neutral.
If you depress the clutch and the shifter is in gear is the vibration still there????

 

[awasson]

If you have not already checked, make sure the the input shaft fits the crank bearing correctly.

It’s currently got no transmission attached but yes, I have a new input shaft bearing for it when I install the 5 speed and I’ve checked it on the 5 speed to ensure it fits correctly.

In other news, I had a haphazard sleep last night because that little disruption between 1400 - 1600 wouldn’t leave me alone and then it hit me at about 3am. I think I know what the issue is…

I’ll bet my distributor’s centrifugal advance comes in at around 1600 RPM and the engine would prefer centrifugal kick in at 1400 RPM. That would explain the on/off switch nature of the disturbance.

It’s pouring with rain this morning (of course) so I’ll have to put on my rain gear to continue with my work but I’ll check my notes on which springs and bushings I have in the distributor. I’ll bet that’s it.

 

[Frank]

vibration in the car will be less with the rear of the engine strapped and isolated from the vehicle. Thanks for the thread, keep dry and keep us posted.

 

[awasson]

So it vibrates not moving & the the shifter is in neutral.
If you depress the clutch and the shifter is in gear is the vibration still there????

I’ve got the transmission out of the car now so it’s only got the clutch and pressure plate attached now.

I think there were two things going on. The transmission was one thing (in or out of gear). It seemed to be the big problem. After I removed it, the engine will go through the Rev range much more smoothly but the underlying other problem I think is the distributor curve. I think the engine needs the mechanical advance to come in earlier.

 

[drag-200stang]

When you get the new bell-housing and trans. adapter bolted down , it is a good idea to bolt a strong bracket to flywheel and dial indicate the trans pilot hole. Not uncommon to be off. The dial indictor must not flex under it weight as you turn the crank. If off you will need custom offset dowels.

 

[drag-200stang]

It’s currently got no transmission attached but yes, I have a new input shaft bearing for it when I install the 5 speed and I’ve checked it on the 5 speed to ensure it fits correctly.

In other news, I had a haphazard sleep last night because that little disruption between 1400 - 1600 wouldn’t leave me alone and then it hit me at about 3am. I think I know what the issue is…

I’ll bet my distributor’s centrifugal advance comes in at around 1600 RPM and the engine would prefer centrifugal kick in at 1400 RPM. That would explain the on/off switch nature of the disturbance.

It’s pouring with rain this morning (of course) so I’ll have to put on my rain gear to continue with my work but I’ll check my notes on which springs and bushings I have in the distributor. I’ll bet that’s it.

Could be, but I would not think that it would cause it, unless way off, but you never know, leave no stone unturned.