Good/Bad news for DR TC sets

[CNCguy]

The good news is the billet double roller TC sets are done except for the clearance gages.

The bad news is that in my attempt to minimize grinding of the front cover for chain clearance, I overlooked the amount that the crank protrudes from the block. Use of the DR setup will require the crankshaft to be removed and the front journal cut on a lathe. A larger than stock radius (.25R instead of .18R)
can be used thereby eliminating any risk of creating a weak point. It should be a low cost operation that can be performed by most any machine shop. Even with the chain pushed back, some front covers may require some grinding. Of the covers I have measured the depth has varied around .035".

I really wanted these to be a bolt on item but GM just didn't allow enough room in there to make it happen. Below is a drawing detailing the required crankshaft modification.



Edit - Update 5/18/08:

I just finish removing, modifying and reinstalling a crank in a '96 3100. It cleared with no grinding at all. The modification to the crank consisted of putting the crank in the lathe, lightly chucking on the flywheel locating hub, put live center in opposite end, machined per the attached drawing and took less than 15 minutes. Most any shop should be able to do this for around $30. I have added a pic of the crank after modification.

This engine has a broken camshaft and lots of cam bearing wear from bad LIM gaskets and high miles. The worn out bearings allow the cam to drop down, leaving lots of slop in the chain. Even with all of this slop and pushing fairly hard on the chain, I was unable to make the chain contact the block. Below are a couple of shots showing chain to block clearance.

Both front covers that I have here will clear the chain with no mods or gasket but it is pretty close and I would like to see a little more clearance. The shortest cover has about .020 clearance without the gasket but I would like to see around .060" to allow for the chain flopping around after if gets some wear on it. The areas between the sprockets require the most clearance since the chain is held in position while it is on the sprogket. I was thinking that a PDF template could be made that can be printed, cut out and used to mark areas that need ground/cleared on the cover. I have added a pic showing how close the cover is to the chain (taken without a gasket).

I cut up a front cover for illustration. You can also see that this cover is .89" deep around the top gear and only requires grinding at the middle and bottom as it is only .86" deep. On a fresh engine this may be ok but some rubbing would most likely occur after the chain starts to stretch and settle in. The left section of this picture is a little deceptive at the bottom since the chain is sitting a little further back under the cover than the top part of the pic.

As you can see in this pic, if the chain had been moved out enough to clear the crank journal a lot of material would need to be removed from the cover leaving it very thin.

One last thing that I should add is that a few sets have already been shipped to Ben.


I will post finalized instructions when they are finished but the basics would be as follows:

1) Remove crank and modify per the drawing below.

2) Use gage that is supplied with TC set to check chain to block clearance and possibly grind block if needed.
The blocks I have measured so far would require no grinding with the exception of maybe the oil galley plugs.

3) Using a straight edge and scale/calipers, check chain to front cover clearance and grind as needed.
Required depths are .87 deep around the sprockets and .90 deep in the middle areas.

[Alxsmt]

well that kinda sucks! but i still want one... how long till they go on sale?

[Superdave]

That's really not that bad..


Have you modified a crank to double check everything yet?

[CNCguy]

Have you modified a crank to double check everything yet?

Not yet as I have to finish tearing an engine down when I have some time. I did install a set by spacing the lower sprocket out .03". With the exception of sprocket misalignment, it looked really good.

I did find that the LZ engines will require more mods to use a DR TC set. GM left more material in the block around the top three holes that mount the front cover. I am working on an alternative way to use a 3400 cam in a LZ engine instead making billet cams.

[IsaacHayes]

Will the 3400/etc timing cover fit a 3900/3500VVT engine? I would think not with the different cooling routing. I'm guessing the cam phaser will hit the car in the L and J bodies..

[zofo61]

I want a set as soon as they are ready. Has a price been set and are you going to confirm the machining before selling them.?

[silvergtjrad]

MMmmm glad to see these are done. I dont think the machining is that big of a deal. Most people looking at a double roller timing set are already into some big dollar mods and the cost of such little machining wont be that big of a deal. I cant wait until these are on sale in the store.

[CNCguy]

See first post for updates.

[blackbombshell95]

With the oilpan off of the block how hard will it be to remove the crank?? That is what matters the most to me.

Thanks for the update Marc.

[Superdave]

remove the 4 main caps and oil pump, and also the rod caps.. keeping them in order of course. Also you'd probably have to remove the timing cover...

it's pretty easy to get it out, maybe 20-30 minutes if it's on an engine stand.