Rover v8 crank nose and supercharger.

j.johnson23 · Post by **j.johnson23** » Wed Nov 27, 2013 8:18 pm

I have been thinking about supercharging the v8 but have a reservation regarding the crank nose,specifically the keyway.
I have heard the key can shear causing the pulley to spin which either snaps off the nose or welds the pulley to the crank.
Is this just urban myth or a real problem and if so is there an answer?
Cheers.

kiwicar · Post by **kiwicar** » Wed Nov 27, 2013 9:33 pm

Hi
it can do other interesting things too . . Just ask Perry (MGBV8)
What are you going to run? street or race? how much boost?
There are quite a few things you can do to help it along, put in a wider/deeper key, put a second key in at 90 degrees to the existing one put a slipper clutch on one of the pulleys in so if it backfires it doesn't snap load the pulley.
Best regards
Mike

j.johnson23 · Post by **j.johnson23** » Wed Nov 27, 2013 9:48 pm

I was thinking an m112 off an XKR.
2:1 RATIO.
Blow through, via a pair of SU`s.
Diverter valve so pressure is off when throttle is closed.
I made a system using an m45 of a mini cooper and an mg montego turbo carb on a Ford XR3i engine years ago and it worked very well,never considered the issue with the crank pulley as it did not have a problem.
A tight fitting crank pulley would help as would adding another keyway.
Thanks.

mgbv8 · Post by **mgbv8** » Wed Nov 27, 2013 9:58 pm

As the Kiwi says!
Depends what you intend to do with the blower and the car. I did have a recent breakage. But it was the pulley itself. The crank and key on the 3.9 were fine. The pulley was my original 38 year old 3500 jobbie. The pulley split along one side of the keyway and caused a bit of aggro.

I hit my pulley hard off the line with boost and nitrous which obviously took its toll on the old metalwork. And the pulley has been drag raced for 10 years now so I'm not surprised it let go to be honest.

And my blower is a bit of a lump as well. So I guess the stress on the pulley when I spin the blower up to 5000rpm and chuck in a 175 shot of nitrous off the line is quite high.

mgbv8 · Post by **mgbv8** » Wed Nov 27, 2013 10:02 pm

j.johnson23 wrote:I was thinking an m112 off an XKR.
2:1 RATIO.
Blow through, via a pair of SU`s.
Diverter valve so pressure is off when throttle is closed.
I made a system using an m45 of a mini cooper and an mg montego turbo carb on a Ford XR3i engine years ago and it worked very well,never considered the issue with the crank pulley as it did not have a problem.
A tight fitting crank pulley would help as would adding another keyway.
Thanks.

I dont think a tight fitting crank pulley will do anything other than being a pain in the arse to remove. For the application you suggest above I think you are worrying over nothing

Perry

Eliot · Post by **Eliot** » Thu Nov 28, 2013 8:09 am

Look up "LS1 Crank pinning" - you drill a hole down the front of the crank between the crank and pulley - simple.

Photo's a few posts down this thread:
http://ls1tech.com/forums/conversions-h ... ild-3.html

stevieturbo · Post by **stevieturbo** » Thu Nov 28, 2013 10:01 am

Pinning is basically just a DIY keyway, and much easier to do.

Even LS engines which are an interference fit pulley need keyed or pinned with a blower.

Although a very low boost or mild setup might be ok on the interference fit alone.

112 is a fairly small blower, so shouldnt be too hard to drive. Not sure how you're going to arrange a blow through carb setup with one though.

But as doing the DIY pinning is easy, makes sense to go ahead and just do it to be safe. Just do one pin opposite the main key, or you could do 2 either side of the keyway

topcatcustom · Post by **topcatcustom** » Thu Nov 28, 2013 5:15 pm

I'm not a fan of using round pins as a key, in theory the pulley is always trying to ride over the dowel, with a square key it is a solid face that prevents turning. I'm sure it would be fine most of the time in practise but the theory is not ideal.

I used a standard square key on mine and it ran a 4-71 with 2" wide toothed belt with no probs, if you are using a ribbed belt on an M112 I don't think you have a thing to worry about.

stevieturbo · Post by **stevieturbo** » Thu Nov 28, 2013 5:28 pm

topcatcustom wrote:I'm not a fan of using round pins as a key, in theory the pulley is always trying to ride over the dowel, with a square key it is a solid face that prevents turning. I'm sure it would be fine most of the time in practise but the theory is not ideal.

I used a standard square key on mine and it ran a 4-71 with 2" wide toothed belt with no probs, if you are using a ribbed belt on an M112 I don't think you have a thing to worry about.

It's easy, it's strong, it's cheap and it works. And IMO in some ways actually better, because the pin used is a complete snug fit into both slots, whereas with a generic keyway, there is potential for a larger tolerance.

Now try cutting a square keyway into a crank and pulley when the engine is still bolted into the car. That isnt easy !

topcatcustom · Post by **topcatcustom** » Thu Nov 28, 2013 6:04 pm

I agree it is better than nothing by a long way, but not as good as a square key! If the pulley were to crack from the drilling to the outside for example it would wind itself over the round dowel and make a right mess, can't happen with a key!

Saying that I would (and possibly have) do it if there was no other easy option.

stevieturbo · Post by **stevieturbo** » Thu Nov 28, 2013 6:07 pm

topcatcustom wrote:I agree it is better than nothing by a long way, but not as good as a square key! If the pulley were to crack from the drilling to the outside for example it would wind itself over the round dowel and make a right mess, can't happen with a key!

Saying that I would (and possibly have) do it if there was no other easy option.

People have sheared key's and pulleys too destroying both crank and pulley.

That's why some will move to double keyed cranks and pulleys. Big blowers can place huge loads, and that's even when the pulley is an interference fit too.

Some will even use 3 pins if they think it demands it.

Eliot · Post by **Eliot** » Thu Nov 28, 2013 7:48 pm

when its all said and done the std oem key will drive a the 112 without any problems i think.

stevieturbo · Post by **stevieturbo** » Thu Nov 28, 2013 8:06 pm

I would think so too

IMO the hardest thing on blower drives is on/off throttle movements at high loads/rpm.
These will be made worse with a manual gearbox. Autos' would be much softer

mgbv8 · Post by **mgbv8** » Thu Nov 28, 2013 9:37 pm

Eliot wrote:when its all said and done the std oem key will drive a the 112 without any problems i think.

My thoughts as well Eliot

I dont think this blower will put enough strain on the pulley to be a problem.

Hanng on!! Doesnt that blower use a groove belt as opposed to a toothed belt??

If it does then the belt will burn up long before a crank pulley lets go eh

topcatcustom · Post by **topcatcustom** » Fri Nov 29, 2013 6:21 pm

7 or 8 rib serp belt IIRC