"Tip Time" by Keith Calver

Some years ago whilst racing in the National Mini Miglia Championship I came across an odd problem that had me a little puzzled for a while.

I built a new engine ready for the beginning of the season from all new parts except for the block, crank and head casting.  I duly ran this in a Snetterton, calling in to visit Peter Baldwin at Marshalls of Cambridge for a final rolling road tune up.

The engine performed faultlessly for 4 races, giving good power and was very smooth, allowing me to use 9,100 rpm on occasions.  At the next race meeting I went out to do the practice session, did a few warming up laps, then registered a vibration from the engine.  Oil pressure OK, water temperature OK, but it would not pull any rpm and got very rough over 5,500 rpm!  I pulled into the paddock having done enough laps to qualify, albeit way down the grid.  A check of all obvious things was made, then pulled the flywheel assembly – no problem visible, crank still in one piece etc.  Put it back together again.  Started no problem, clutch worked OK.  Oil pressure, etc., OK. Compression check – OK.  Not much else I could do.  I lined up for the race.  Lights change, off we go.  Still won’t pull any rpm.  Still as rough as it was.  I persevered for a few laps but obviously not going anywhere – so I pulled in to avoid any further possible damage.  Oil pressure etc., still OK. Somewhat frustrating to say the least.

Back home, out came the engine, full strip, crack test and rebuild.  Next meeting out to practice – exactly the same problem!  I wasn’t entirely surprised as I hadn’t found anything wrong during the strip/rebuild.  I didn’t think it’d go away on its own.  I pulled back into the paddock, large cup of coffee and a good think were in order.  OK, take flywheel off again.  Before I got that far, a wise old man whispered in my ear “drive straps” and walked off.

I took the cover off, removed the diaphragm and examined the clutch drive straps.  Didn’t seem to be anything wrong.  Get the Vernier calipers out. “Well bless me” I said (?).  Sure enough one pair had stretched.  Only by 45 thou, but definitely stretched in a sort of curve.  I put two new straps on, reassembled the clutch, etc. and went for a test run up the air strip (at Silverstone).  Back to original performance.

Went out and did the race that afternoon fired with enthusiasm, started almost at the back of the grid and finished 12th.  Needless to say I was somewhat pleased as I loaded the car onto the trailer.  As I was tying the car down, the wise old man came past again and whispered “use three on each”.

From that day on, I have always used THREE clutch straps on all race/rally or serious road engines, I have built.  Never had the problem again.  Thanks Phil!

Keith Calver