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

[awasson]

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.

That’s a darn good idea. It hadn't occurred to me that it would be off but with adapters and swaps, anything is possible.

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

Well, the big problem went away when I removed the 3-speed transmission. I really didn’t even notice this disturbance at 1400 - 1600 until the transmission was out but now it’s so smooth when it comes off idle that a slow acceleration in the revs is quite noticeable as soon as it hits 1400. The steering wheel starts vibrating and then it’s completely gone at 1600 and it continues to rev smoothly.

 

[awasson]

Well... I'm putting on my rain gear so I can pull the bell and get the flywheel to the machine shop to have it surfaced.

Further to this disturbance I'm trying to track down, I've attached an image from the HEI distributor tech notes. I have it using the stock silver springs and silver bushings which I have annotated on the image, highlighting the centre of where the trouble area is (1500 RPM).

It's showing that in the middle chart noted as Chart D which is my current settings. From my view it looks like at 1500 RPM those springs have the ignition advancing about +6° and it peaks at +16° centrifugal at 3000 RPM.

The chart at the bottom, Chart F shows the curve response using the Gold Springs and it shows much more early centrifugal advance at that trouble area. It looks to me as though it is advanced at about +12° at 1500 RPM. That is a pretty significant change between the silver and gold springs and it will reach max +16° centrifugal at 2000 RPM.

 

[Frank]

Up to detonation, the earlier the better IMO.

 

[awasson]

Well, a little more progress and I’m really optimistic. I haven’t done anything with the distributor and timing yet. I wanted to swap in the new clutch and pressure plate and see how it responded first.

I took the flywheel in this morning and had it skimmed. It was very level and only had a little glazing.

The new clutch and pressure plate is from rock auto and it’s a 1978 Ford Fairlane clutch kit with a diaphragm pressure plate which will work with the T5 I’m installing. I put it back together this evening after work and it’s just waiting for the adapter to put in the 5-speed. The clutch is aligned and everything is torqued with locktite.

I fired up the car and it is very smooth now. There is still a slight anomaly around that 1400, 1500 range; you can still feel a little vibration and there is an audible hum that comes with it but it doesn’t shake the steering wheel the way it used too with the old clutch and pressure plate and it’s a whole different story from where it was with the OEM 3-speed manual.

I’ll spend a little while getting the tune right and maybe I can tune the vibration out with fuel and timing. It’ll be interesting to see how it responds with the 5 speed connected.

 

[awasson]

Further on the topic of timing, I talked to tech support at Clay Smith this afternoon. I don't recall who I talked to but I recognized his voice and I have talked to him before. He was really helpful in helping me get my cam degree'd last summer. He said the H-6474-0-B cam I've got is a pretty aggressive grind and that camshaft was actually designed for Matt's Vintage Inlines Aluminum head so it's difficult to dial in on a log head with a 2V carb. I think I need to source an Aussi 2V head or one of Matt's when I refill my play dough account

He said he figured the Weber 38/38 was a lucky choice because it is working pretty well and he thought a Holley would be a harder carb for getting dialled in. He figured with a Holley, you'd want a smaller power valve to more gradually enrichen under load.

As far as timing goes, he suggested getting all timing in as soon as possible, basically saying get it all in between 1200 - 1500 and having about +35° total timing. That may very well explain the anomaly that's centred around 1500. With that info in mind, I'm going to redo my base carburetor tune with the small idle jets and then I'll set my advance somewhere around +18° and move to those gold springs. It'll get the timing in quicker.

Any comments or advice are greatly appreciated.

 

[awasson]

Ok, a little more progress.

I've reset my tune with Weber #55 pilot jets and set it up according to my notes. Then I warmed it up, got it to a decent idle speed before ported vacuum advance kicks in. I retarded my initial timing to about 18° - 20° and adjusted for best lean idle. It's the best idle I think I've ever managed since I put it together. It idles at about 800 RPM, it's a little lopey but not uncomfortably. If it were an automatic, I don't think I'd be happy though.

Then I changed the advance springs to the lightest in the HEI distributor kit. I still have that anomally at 1400 RPM but it is pretty slight with the transmission out of the car. There is a small vibration to the steering wheel but I couldn't film it and it's gone by 1600 RPM.

On another note, I'm going to change the title to the correct RPM range now that I know where it is.