[Tom63LeMans]

I have a ‘70 400 that was set up as a low boost blown street engine. It’s an interesting engine as it has heavily modified 1959 heads and early Weiand manifold and 671 blower. Assembly was discussed a while ago on this post; https://forums.maxperformanceinc.com...d.php?t=850881

I just took the crank to my machine shop with a newer style double keyed hub to have the second key machined in the crank. I was not aware but he informed that both keys in this hub are 1/4”. I saw some previous posts that recommended using two 1/4” keys. The question I have is how should the crank be machined for the key ways? Mainly what type of keyway and key is used for the primary key that positions the timing gear. Are they straight keyways instead of woodruff style.
I also have the hub that came with the engine that has a single 3/16” keyway. My preference is to be able to use either hub on the crank. I see that BDS offers hubs with both 3/16” & 1/4” keyways but I’d prefer to use what I already have.
Thanks in advance.

[Jack Gifford]

You'll need to decide what route to take. All I can do is relate my experiences with a 6-71 on Pontiac V8s, mostly the M/T hemi. First off, two keys aren't needed for a 6-71. My hemi (370 c.i.) made 900 HP (sometimes to 9,000 RPM) for eleven seasons using just a single 3/16" key. I always used one full-length key to drive both the timing gear and the blower hub, to reduce stress-risers at ends of the keys.

[mgarblik]

Originally Posted by Tom63LeMans

I have a ‘70 400 that was set up as a low boost blown street engine. It’s an interesting engine as it has heavily modified 1959 heads and early Weiand manifold and 671 blower. Assembly was discussed a while ago on this post; https://forums.maxperformanceinc.com...d.php?t=850881

I just took the crank to my machine shop with a newer style double keyed hub to have the second key machined in the crank. I was not aware but he informed that both keys in this hub are 1/4”. I saw some previous posts that recommended using two 1/4” keys. The question I have is how should the crank be machined for the key ways? Mainly what type of keyway and key is used for the primary key that positions the timing gear. Are they straight keyways instead of woodruff style.
I also have the hub that came with the engine that has a single 3/16” keyway. My preference is to be able to use either hub on the crank. I see that BDS offers hubs with both 3/16” & 1/4” keyways but I’d prefer to use what I already have.
Thanks in advance.

There are several ways to deal with this. A rather novel way we dealt with a Moldex billet crank was this. It had the long, stock 3/16" keyway already machined in the crank. We had a 1/4" square keyway cut 180 degrees away. Then we had a 1/4" square keyway cut right on top of the long 3/16" woodruff keyway about 2/3 the length leaving the 3/16" part of the keyway where the timing sprocket goes. Then I put the long woodruff key in the mill and machined the top down about half way back flush with the square keyway but filling the woodruff groove. Then put a hardened 1/4" square key on top of it. Worked fine in the high HP nitro application and was pretty simple to do. If this doesn't make sense, I can take a picture of the "step key" I made and post. Slightly hard to explain.

[mgarblik]

Here are some pics that may be helpful to your project Good luck.,

[Tom63LeMans]

Originally Posted by mgarblik

Here are some pics that may be helpful to your project Good luck.,

Thanks., the picture’s definitely helped. I’ll take this info back to my machinist.

[Steve Barcak]

Mike,
am curious if you had a failure in the hub/snout/keyway area prior to this idea/mod? Or just did the upgrade to strengthen the area?

Originally Posted by mgarblik

Here are some pics that may be helpful to your project Good luck.,

[mgarblik]

Originally Posted by Steve Barcak

Mike,
am curious if you had a failure in the hub/snout/keyway area prior to this idea/mod? Or just did the upgrade to strengthen the area?

We never had any crank nose or keyway failures with any of the crankshafts we ran. What drove the decision to make the funky keys was we had 2 custom made RCD hubs with 1/4" square keyways and a moldex crank with a 3/16" stock keyway where the timing sprocket goes and a 1/4" keyway cut on top of the 3/16" keyway where the OE balancer would normally go. So it was a search for the easiest way to make all these parts fit and be accurate and reliable with minimum machining. With the Crower crankshafts that we custom ordered, I just asked them to cut a 3/16" short "Chevy" style keyway for the timing gear and 2 1/4" keyways for the hubs. That was a nice solution instead of a band aid. But no issues either way.

[Steve Barcak]

thanks for the reply. best to you