v6 cam drive

As promised here is a new thread on the life definitive question of "gears or chains".

I once had a Dino that used a straight cut gear set off of the nose of the crank to drive the first motion chain wheels which in turn drove the four cams. The whining sound of the gears has never left me.

In order to capture that part of my ill spent youth I am considering devising a gear set for the 3.4 that will eventually end up in the Fantasy Ride MGB.

The problem is that no one makes a gear set for the narrow six and it looks like I will have to modify one that was intended for a V8.

There are two basic arrangements. One uses a single idler gear and the other a set of twin idlers.

Here are illustrations of the two. Whoops, I am a non-star low life so there is only one image here, but I'll post the other on a companion thread.

Anyway, the dimension between the center lines of the V8 and V6 are different. The V8 is about 5.2" and the V6 is a little over 6".

My first thought was to begin with the twin idler set up and just bring the idlers closer together, thus effectively "squeezing the cam and crank gears apart. I posted the idea somewhere and a respondent said that in doing so it would have to be just a coincidence if I could get the cam timing correct. My thought was that it didn't matter where the idlers were position as all they had to do would be to mesh properly with the other two gears since the rotational relationships would remain the same. But then I am just a country mechanic, not a mechanical engineer so who knows?

Then someone posted information on the single idler Summers Brothers arrangement, the image in the other thread, and that looked like an easier thing to deal with, just change the support plate to spread the cam and crank gears to where I wanted them and move the single idler inboard to the proper position.

Why am I typing all of this? I don't know exactly, but the idea intrigues me and I guess that I hope to get some rational feedback here from some of our most learned and more straight thinking members.;)

Any comments would be appreciated.

Jack

Jack, the Cloyes type should do the job for you much easier than trying to build a frame work for the single idler Summers Brothers type. I agree, moving the two idler gears closer together should effectively lengthen the gear train without affecting the timing relationship, after all the center gears are just idlers and don't have any effect on the overall gear reduction between the crank and cam gear.

Jack;
I love that sound.

From my understanding, the idler doesn't change the speed or timing of the the two gears it touches, just the relative rotation. With an idler, they both spin the same direction, without an idler, they spin opposite directions.

So, the idler gear diameter makes no difference to anything. You can place the idlers anywhere they fit and it will work the same.

Larry, an idler gear has no effect on the overall gear ratio, it just transfers motion between the drive and driven gears. In the photo of the Cloyes setup you'll notice that the dual idler gears are of different diameters. If they affected the ratio then they would bind up. As it is the smaller idler just turns a bit quicker than the larger idler does.

Neat idea. I have the idea of the sound in my head and can see where this is going. (tu)

-BMC.

Yeah, The gear whine might make some think there is a supercharger under the hood!

Since this is a "cam drive thread"...

If you have the time and energy to make this gear drive work, go for it. But if you want to simply upgrade the cam chain setup, grab the tensioner from a 3.4l DOHC engine (Lumina, Monte Carlo, Grand Prix GTP I think etc) and toss it on with the chain of your choice. Why didn't all RWD engines have this??

This won't work for FWD timing covers (the tensioner is too deep to fit under the compact FWD covers), but I used one for years under the RWD timing cover on my pushrod 3.4. I'm sure it made no difference, but I felt like I'd tried anyhow! :)

Got it. I was thinking of the 3 sheave setup in my drill press. I forgot that I am running off two different diameter sheave sections in the center. Color my brain old today.

The difference in idler diameters might help in the "climbing" department.

I have never been into the front end of a 3.4 so I have a couple of questions.

1...Does the nose of the V6 crank resemble the look of the crank gear in the Cloyes photo?

2...Does anyone know the two diameters of the V8 and V6 nose?

3...Is the cam gear in a V6 attached similarly to the V8?

4...I suppose that the idler in the Cloyes set-up just sits there and floats, being kept in line by the width of the twin set fitting closely to the inside of the gear cover and the front plate of the engine. Right?

Jack

Jack,
The SBC and 60V6 have the same diameter crank gears and the keyways are the same width. The thickness of the gears from the crank face to the dampener face are very close with the SCC being .523" and the 60V6 being .528". The cam gears are also very similar in how they mount with the exception of the drive pin. The SBC pin is .25" compared to the .236 pin in the 60V6 cam.

Your biggest issue will be getting gears to clear the block and TC cover. As you can see the 60V6 has a larger crank to cam centerline without much clearance for the upper gear. This has been a big issue for us in coming up with a single roller setup for the FWD engines. We currently make a double roller setup but it requires modification to the crank nose as well as grinding of the block and TC cover.

I attached a pic of a SBC single roller next to a 60V6 Cloyes double roller and a drawing showing the cam gear to block/cover clearance on the 60V6.

Let me know if you need any other information.

Thanks tons Marc !

Re: The issue of clearance between the top arc of the straight cut cam gear and the inside of the timing cover. What is the radius of the center-line of the cam and the uppermost point of the assembled stock chain wheel and chain?

Re: Similar issue a the bottom of this mess. What is the radius of the assembled crank chain wheel and chain?

And of course, what have you measured as clearances within the cover for both?

It seems to me that a "bump out" of the upper, and lower for that matter, partial arc of the cover might do it if the back side surfaces of the gears are sufficiently far away from the plane of the cover mounting flange.

The problem with the difference in drive-pin diameters could be overcome by drilling out the opening in the cam flange.

Not sure that I understand: "The thickness of the gears from the crank face to the dampener face are very close with the SBC being .523" and the 60V6 being .528"." Do you have a side elevation drawing of this?

If we can get by this stuff, I suspect that you might be able to do the math and make up a new speader bar for the Cloyes idler gear set. Yes, no, maybe?

I think that I'll go to the barn and have lunch.;)

Jack

Have you consider a belt drive instead of the old school roller chain??

Jack... I put another drawing together using measurements from a 3.4L Camaro cover. They should be accurate within .015". You could do some grinding to gain a little more room but .060" would probably be the most.

The upper bump is part of the cover to allow plenty of gasket area between the coolant passage and the inside of the TC cover. The lower bumps in the first drawing were for the FWD engines and not relative to your application (I forgot to remove them the first time).

You may be able to open the hole in the cam for the drive pin but would most likely have to add another hole in the gear since the timing of the gears will change as the idler gear location is changed.

I don't have a side view for the RWD application but will say that the crank gear goes onto the crank first and the dampener seats against the crank gear when you tighten the dampener bolt.

The dual idler gear with spreader bar setup will not work with this setup due to the long cam/crank center distance. As the center distances increases, the idlers move inwards and will hit each other (as shown in the light blue). Larger crank and cam gears help but it is impossible to get the right combination according to my gear guy.

A single idler on the right side of the engine could possibly work but securing it will be a problem unless a custom TC cover is made. There are two M8 holes in the front of the block that you may be able to use if the gears are moved forward a little.

I looked at this in the past but dropped it due to costs and the gear noise interfering with the EFI knock sensor. Eliminating the EFI users would really limit the market.


Bill... I had tossed around the idea of a timing belt setup but set it aside for a few reasons. Timing cover clearance on a FWD engine is a huge issue and, like the timing gear setup, it would be fairly expensive thus creating a very limited market. It's a catch 22, it requires high volume to get low prices but the demand isn't there because there are few parts and they are expensive. I don't really see the demand picking up since they have stopped producing these engines. If there were a big demand, all the big companies would be making parts.