Box Stock

Question about flywheel slipping

R

racer10

Member
I put a box stock project short block together last year with a pvl flywheel torqued to spec no key in it slipped after about 15 minutes of break in time got a arc flywheel over the winter set it up same way no key new starter cup and nut torqued to spec went to local practice track yesterday just fool around and it slipped to not sure what's going on with it just put a #3 key in and going to run it in the Briggs days I never ran a key and never had a problem 1 st clone I ever put together any ideals why this would happen was lapped and torqued to spec
 
I lapped and put an advance key in my big block with an arc flywheel. It still bent it some with the proper torque specs they say to use. So I guess up the torque specs it is then.
 
Ours held the first couple of times I installed them. Think compression will have an effect on it also. Cant say for sure.
Last few times on & off I have had to use a offset key also. Just my observations.
 
Heat the center of the flywheel and spray the crank with CO2. Torque to 70ftlbs. Do not use keys as they can be the reason it slips. I have noticed that sometimes the crank taper is off a degree. If everything else fails change the crank.
 
Lap well, make sure the entire crank and inside bevel of flywheel is well lapped and making contact. then Use Acetone to thoroughly clean the crank and the flywheel. I usually torque to about 80 ft. lbs.
Plus make sure that your torque wrench is accurate! You know the old saying Cheap Chinese Junk!
I am going to try what Renegade said. That sounds like it would work.
 
After tightening them too 75-80 ft lbs . The flywheel is a bear to get off .
My question is how are you holding everything in place . Piston stop or crank holding fixture ? Strap wrench or special tool on the flywheel ?
Or some type flywheel press .
One or the other always seems too move .
 
My flathead flywheel holder works on all the wheels. Not a perfect fit but gets the job done. Set the piston stop so you have the degrees you are after. Place the wheel on the crank where you know the firing point is. Tighten the nut with a socket and ratchet only enough that you have it snug. DO NOT USE THE PISTON STOP AS A METHOD FOR TOTAL TORQUE!!!! Once you have the wheel snug back the engine away from the stop and find whatever way you use to final torque. I highly recommend for the first few times you remove the stop so you don’t make a mistake and wreck the piston until you master the process
 
In my household I have a technician that one of his jobs is calibration of instruments, as for the statement cheap Chinese junk, you should realize in general Asian made torque wrenches are out of the box the most accurate and many name brand well known are most commonly in need of adjustment. Many of the name brand are off shore aquired also. For the person that has the flywheel slipping you must remove it and inspect the inner taper and hub I would guess you have a hairline crack, it likely has been overtightened and even had an impact wrench used on it. For all of the ones that simply say increase the torque, you risk twisting the threaded end off the crank.the flat surface of the nut will apply more force than the diameter of the threads can withstand, it will snap the end off.
 
Lately, I've had the total opposite issue, when tearing down for rebuilds of my engines I am finding it very difficult to get the flywheels off! I fought one yesterday for 20+ mins! All I'm doing is lapping real well, torquing to 75ft/lbs with a new nut and sending it. Never had one slip.
 
70 foot pounds is adequate.
Make sure that the taper matches (ie lapped well.)
Also be sure to thoroughly clean all of the lapping compound off before assembly -- believe it or not, I have had people tell me they thought it should be left on there!

A few years back, I had one of my foot pound torque wrenches go bad, ie was reading high.
Even with runs on the dyno, some of those engines with improperly torqued flywheels came loose at the track = not good for customer relations. Pretty embarrassing when it happened, but what I'm trying to say is, it CAN happen.

I am NOT a big fan of Chinese torque wrenches (or Chinese tools in general.) I understand that some people get along just fine with them, but that has NOT been my experience.
Whatever brand you are using, have it calibrated from time to time, and at the very least compare it to another wrench as a self-check.

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🏁Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
Carlson Motorsports on Facebook
31 years of service to the karting industry
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
 
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