Timing retard - Why

[ksurfer2]

Engine is a 512, solid roller cam, MSD Pro-billet Distributer with locked timing, MSD digital 6 box, Bronze distributor gear. Setting timing at idle (approx 1,000 rpm) to 35*. When any throttle is applied, the timing will retard approximately 5*. There is a cam button on the front of the cam. I do not recall the gap to the timing cover, but I did set it to spec. Could the cam pushing forward and causing the timing cover to flex cause the change in timing?

 

[dan juhasz]

I don’t see how

 

[R/T Boy 67]

If the cam moves in and out it will turn the distributor, which will affect timing.

 

[Dan64]

Probably a stupid question but are you sure that the timing light you are using will work with a MSD box?, some are said not to.

 

[dvw]

Here you go.
Doug
From previous posts;


Different collar, This one goes at the bottom of the distributor shaft and sits on top of the intermediate shaft gear. It eliminates the slop between the shaft and distributor to minimize spark scatter. Like 67Dart273 said, a couple bucks at the hardware store- and Loctite on the setscrew!

I've also heard of people just using a rubber hose cut to proper length to accomplish the same thing, but I've never tried that...

Wow, You guys over complicate things. Here's what I've been doing since the 70's, all you need is a short piece of rubber hose 1/2" ID. Slip it over the shaft, tighten down the distributor, DONE. The hose will keep the intermediate shaft from dancing around and you'll have steady timing instead of a timing mark jumping around 5-7 degrees.

 

[zombezoo]

wouldn't the rubber deteriorate over time and eventually end up plugging up the pickup?

 

[moes]

I've used a transmission rubber line on an old distributor to stop it dancing around and never had a problem with it deteriorating over time. An old guy showed me that trick.

 

[Kern Dog]

wouldn't the rubber deteriorate over time and eventually end up plugging up the pickup?

Even if it did, what if you replaced it every 2000 miles or so?
That is about the life cycle of those bronze distributor gears people often use with roller cams, from what I am told.

 

[Geoff 2]

You do not need a stop on the end of the dist shaft. The direction in which the helical gear is wound on the cam/oil pump drive is such that the drive is pulled down by the load of the oil pump pumping the oil. That is why the drive shaft bush in the block has a large thrust face to take this thrust.
As stated by others, timing variation is probably caused by cam movement. With FT lifters, the offset of the lifter on the lobe drove the cam back against the thrust face on the block.

 

[dvw]

Even if it did, what if you replaced it every 2000 miles or so?
That is about the life cycle of those bronze distributor gears people often use with roller cams, from what I am told.

The bronze gear in my racecar has been in use since 2013. Over 1100 passes.

Geoff 2:

You do not need a stop on the end of the dist shaft. The direction in which the helical gear is wound on the cam/oil pump drive is such that the drive is pulled down by the load of the oil pump pumping the oil. That is why the drive shaft bush in the block has a large thrust face to take this thrust.

With a big block, the drive rides upward due to the counter clockwise rotation of the the helix. Riding upward retards the timing. A small block rotates clockwise so it drives downward. There is a cam button installed. There is no taper on roller cam lobes. So there is no reason for anything to flex forward or rearward.
Doug

 

[70bigblockdodge]

If cam was moving forward it would advance timing. It is probably forward and moving aft. I would look at button clearance. The distributor riding up a bit in the drive slot in a big block could be making your problems. I have always added a 1/2" shaft collar to the bottom like first picture to keep the shaft up in dist.

 

[stage3]

i pinned the collar to the shaft because i dont trust the set screw to keep that collar in place and fall down in my Expensive motor upon dist removal...ace hardware 1/2" steel collar.

 

[70bigblockdodge]

i pinned the collar to the shaft because i dont trust the set screw to keep that collar in place and fall down in my Expensive motor upon dist removal...ace hardware 1/2" steel collar.

TIG tack the set screw, cut the collar at set screw if you need to remove. Pinning it works also.
On a stock distributor you can replace the plastic collar (will break anyway when touched) and adjust out the excessive vertical play on the distributor with a drilled/pinned sleeve or collar.