Roots rotor timing specs

For the first time I am about to retime and restrip my 14/71 std helix magnesium Mooneyham blower, the rotors are only just (appear to be) touching, what running clearances are correct, should there be more on the leading or trailing side of the rotor?

Obviously one needs to strip the teflon out first for proper clearancing but I will leave the nylatron strips in, I have searched other threads and read up on first aid for the injuries I am about to incur by restripping, any help would be appreciated.

Cheers Ray

 

Blower Timing

HI RAY THE WAY I USUALLY DO IT IS THERE IS TWO PADS ON THE SIDE OF THE TEFLON ON THE OLDER BLOWERS FOR SETTING TIMING. YOU PRETTY MUCH ROLL THE ROTORS BACKWARDS OF NORMAL ROTATION TO DO THIS MEASUREMENT WITH LONG FEELER GAUGES. ITS KINDA LIKE ADJUSTING VALVES TO GET THE FEEL. THE RULE OF THUMB IS .010 BETWEEN TRAILING AND LEADING EDGE WHICH MEANS YOU MUST CHECK ON EACH SIDE OF THE LOBE. SOME BLOWERS YOU WILL FIND ARE TIGHTER OR LOOSER DEPENDING ON BORE CENTERS WITH THE BEARINGS,ROTOR WEAR, ACTUALLY SIZE OF ROTOR ETC. THERE IS ALSO THE THEROY OF .007 ON THE TRAILING EDGE OF THE DRIVE AND .012 ON THE LEADING AS THE DRIVE ROTOR IN THEORY IS BEING PULLED CONSIDERABLY HARDER BECAUSE OF THE SNOUT. SO IN THEROY AS THE DRIVE ROTOR TAKES ITS HIT ON ACCELERATION IT WILL HAVE A FEW THOUSANDTHS EXTRA OF CLEARANCE AS NOT TO SMASH THE TEFLON ON THE LEADING EDGE. I HAVE DONE BOTH WAYS AND HAVE NOT SEEN A REAL ADVANTAGE TO THE LEADING WAY. THE WAY TO CHANGE THIS IS BY CUTTING THE BACKSIDE OF THE GEAR TO GET YOUR CLEARENCE. RULE OF THUMB FOR EVERY .001 YOU WANT TO CHANGE YOU NEED TO CUT .003 OFF THE GEAR. MAKE SURE TO CHECK THE SHAFT THAT GOES IN THE GEAR AS SOMETIMES BLOWERS USE STEPPED WASHERS WHICH WILL BOTTOM OUT ON THE SHAFT OR THE SHAFT MAY ACTUALLY POTRUDE THRU THE GEAR AND NOT ALLOW THE BOLT TO TORQUE DOWN THEREFORE YOU WILL NEED TO CUT THE ROTOR SHAFT DOWN ON THE END. GOOD LUCK AND REMEMBER BEFORE YOU START HAVE BAND AIDS READY(I USE DUCT TAPE) AND WEAR SOME GLOVES WHEN PULLING THE STRIPS. IF YOU NEED ANY SUPPLIES WE CARRY THEM ALL WWW.RBSSUPERCHARGERS.COM OR CALL 530-292-3368

 

if you are just wanting to restrip your blower cool if you need to re clearance it spend the $$$$ and send it to mert littlefield or RBS I have a machine shop just for our racing but when it comes to my blowers send them off it will save you a lot of money and worries rotors aren't cheap..good luck

 

Hi JR it's an early morning here in the land of OZ, thanks for your info and the phone call I'll be placing my parts order soon.

The problem here in Oz is the tyrinay of distance (shipping), it's just not viable for an old roots style blower to be sent back to the states.

Cheers Ray

 

Ray,

We do our own 16-71 Hi-helix in West Oz, we purchased a rotor jig that holds the rotors like a spit and we use locking vice grips on one end to pull through the teflon with HEAPS of CRC on it at all times, slow and steady seems to be the key, the jig was the best thing we ever bought i can send you a photo if you send me your email address

marc@contractpower.com.au

Cheers
Marc

 

REMEMBER RAYMOND!!!!!!! always leave around at least an inch past the rotor of teflon. let it set for a few then do a final trim on it

 

Ok this is a dumb question but.

Are you guys talking about the black teflon strips or the white nylatron strips? The blacks need to be turned while on the rotors on a lathe to the case cavity dia dont they? Or is this something new?

 

Good point

 

the black strips are the nyalatron? and the white is the teflon.and yes to redo the blacks you need to chuck the rotor up in the lathe

 

Thanks guys,

Cheers Ray

 

Check with O.G. Speed Shop in Klmzig. Ask for Mr Lennard. He should be able to strip your blower for you. His # is (08) 8261-7700. Hope this helps.
Mike