Lightening flywheel

Any topics pertaining to the BMC A-Series engine.

Lightening flywheel

Postby axafrog » Tue Feb 11, 2014 6:42 am

Does anyone have a drawing or any info on lightening a 1275 flywheel. The tuning booklet mentions 12.5 lbs, is this a reasonable amount? This is just a road going car, I'm just after faster throttle response.
Pit Crew
Posts: 11
Joined: Tue Feb 22, 2005 1:00 pm

Re: Lightening flywheel

Postby HAN5L778 » Fri Feb 14, 2014 11:42 pm

I have 3 1275 flywheels that have been lightened by others. They range from 10.5 lbs to 12.5 lbs. Take your flywheel to a machine shop, with the clutch cover included. They can remove weight from the outer edge to where the clutch cover bolts on. They can also take off some from the backside, but keep checking dimensions and thickness to clutch face. I have seen some that had holes cut or drilled through for lightening. Some work, some act as a fan and suck oil out the rear main. I think it depends on the shape of the holes and maybe the angle of the cut. I would stay away from this option. I have seen steel flywheel as light as 8-9 lbs, but those were for racing. I think your idea of around 12.5 lbs would work well on a street engine. Also have the flywheel, clutch cover and crank rebalanced once the work is done. It's not as critical as in a race engine, but it will help the street engine and not stress the rotating mass. Check in your area and local clubs for racers and autocrossers to find out where they get machine work done.
'69 Sprite-project with lots of trick parts.
'63 MGB waiting for restoration
User avatar
Posts: 320
Joined: Tue Jun 15, 2004 12:24 am
Location: Ann Arbor, MI

Re: Lightening flywheel

Postby Highlander » Tue Feb 18, 2014 3:03 pm

The BMC tuning book has the dimensions for lightening the flywheel. I sued those dimensions and the 1275 bolt and pin pattern to turn an aluminum one. With a steel Tilton insert,, all of the helicoils and backing nuts for the insert, and the ring gear, it weighs 8.4lbs and truthfully is a bit too light for road use, starting up on a steep incline is an exercise in slipping the clutch. :oops:
Mark Haynes
User avatar
Posts: 60
Joined: Fri Feb 05, 2010 2:05 pm

Return to A-Series (948cc, 1098cc, 1275cc)

Who is online

Users browsing this forum: No registered users and 1 guest