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Donington Classic Sports Car Club - 30th May 2021


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The CSCC meeting on Sunday 30th May 2021 has a Swinging 60s race with 2x TR6, 1x TR5, 1X TR250 and 2x TR4s among the 31 car entry.

The Future Classics race has a TR7 V8.

The Classic K race has 2x TR4.

Spectators are now allowed into the circuits, with care. Come along for a good day of Classic car racing.

Dave McD

 

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Thanks for the heads up on this event. I hadn't been to Donnington for ages and what a good track it is for spectators. Some great racing throughout, especially the swinging 60's. Mark Campbell's pole sitting TR5 was outdragged to the first corner by a splendid Corvette. The TR5 squeezed past the Corvette, but never reappeared for the next lap which was a great shame, the assumption being that something had broken on the car.

Nice to see a number of TR's racing along with Sunbeam Alpines, MG's and Minis. Thanks to all the competitors.

Jerry

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44 minutes ago, Dave McDonald said:

Jerry,

Mark Campbells' TR5 suffered a broken camshaft timing sprocket, caused by harmonic vibrations from the crank at high revs - ask me how I know!!

Dave McD

Does that not beg the question about the sprockets you are using?

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On 6/3/2021 at 8:28 PM, ntc said:

Does that not beg the question about the sprockets you are using?

The vibration is due to the firing impulses causing resonance in the crankshaft.      I would question the crankshaft damper more than the cam sprocket.   

John

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On my new race engine, I lost 2 cam chain tensioners, a cam chain & the oil pump drive last year, steel crank didn't rev over 7k running with a Sterling damper from Vibration Free, any ideas ??

 

Andy

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I've seen several mentions that modern repro chain tensioners wear out vey quickly due, I presume, to unsuitable material.     That might lead to accelerated chain wear, and failure, rather than any torsion vibration.      And the Stirling damper is a 'pendulum' damper that has a wider range than the OE viscous rubber type, so better suited to a steel crank that will have different harmonic properties to a cast one, so again, torsion vibration is  less likely to be the cause.

If the camshaft drive fails, then so will the oil pump drive.    No further explanation needed for that!

JOhn

 

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Thanks for the reply John.  The first broke on my third test session on the new engine, just above the mounting, broke up and wrapped itself round the cam sprocket, causing the valve timing to jump, the second was a different material, again broke at the mounting but stayed in one piece and wore through the the cam cover spraying oil everywhere during qualifying at Snetterton last August . The oil pump drive actually failed after the cam chain had been repaired 10 minutes into qualifying at Donnington last year. 

 

Andy

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Thank you, Andy!    I presume these were new chain tensioners?       I've never fitted one, always selected the OE one that seemed least worn.      If so, I fear  repeated failure confirms a bad batch at the supplier.      What are you using now?   I may have some old ones that I could send you.

John

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yes a bad day  at Donnington for TRs.   7 entered but only 1 saw the checkered flag .:(

Roy

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On 6/6/2021 at 5:18 PM, roy53 said:

yes a bad day  at Donnington for TRs.   7 entered but only 1 saw the checkered flag .:(

Roy

Yes, fortunately for me, I was the last man standing in a TR.

On 6/3/2021 at 8:28 PM, ntc said:

Does that not beg the question about the sprockets you are using?

Neil,

Poor description on my part. The sprocket itself didn't break. The problem is crank vibration at high revs which pass up through the timing chain into the cam. There are 3 modes of failure:-

1 - The two tynes on the bottom of the distributor drive dog break off

2 - The distributor drive shaft and gear breaks, usually taking teeth off the cam drive gear with it

3 - The cam front spigot which locates into the timing sprocket, c/w the 2 set screws attaching the sprocket to the cam all break. The sprocket and timing chain drop into the bottom of the timing case onto the crank sprocket.

Despite having an ATI harmonic crank damper from the USA fitted I've suffered all 3 types of failure. No 1 easily rectified, 2 & 3 not so. The ATI damper works well to a point, but continuous use of 7200 rpm for prolonged spells stretches its' capabilities and the damper must be serviced regularly with a new rubber O ring kit to keep the rubbers supple as they become dry and brittle with the enormous heat build up in service, losing their effectiveness. I now do mine every 2 seasons and avoid the temptation to give it max revs, particularly as the peak power and torque are at 6800 rpm anyway. An early indication that something may be amiss is when a fan belt throws off.

Dave McD

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