Drive chain

[frankseddon]

Hi fellow ME  owners - can anyone confirm if the drive chain is a standard Renold triplex 3/8" flat sided (06B3)? If it is mine has stretched by 12% - is that unusual?
I am looking to replace the chain and can only buy 10ft from Renold whereas I would need only some 66 x 3/8" = 25" . If this is the correct chain is anyone else interested in a replacement?
Furthermore I have been advised with the relatively small sprockets (24 teeth) these should be OK to be reused - the larger the sprocket the more the teeth will become out of sync with the stretched chain, thus the more the sprocket wear. Any views and are sprockets available anyway?

[administrator]

The chains have a long life (often 100K miles plus) but do stretch eventually.

Renold discontinued the 3/8" chain and AC at Brooklands developed a conversion set to use 5/16" chain with new chainwheels to match.  Further batches have been manufactured for the ACOC. 

The original chain is described as Renold Chain No 116513, 0.4375 Pitch, Triplex 66 pitches long, riveted endless, Renold drawing K3875.

A good idea to contact Ian Winter and John Spencer for more info.

Bryan

[frankseddon]

Thanks for that Bryan, although it does leave me a little confused! I presume the early cars had 3/8" (0.375") and the later cars had 5/16" (0.3125"). My chain measures 10.91mm (0.43 or 3/7") with a 0.4% difference when stretched vs compressed, which would suggest little wear. So despite being one of the last cars from Thames Ditton would appear to have an original (116513) chain???
No need to replace it with a 77k mileage?

[ACOCArch]

The original from AC Thames Ditton described by Bryan Moseley is correct except that the pitch was 7/16inch. The chain and probably the chainwheels were Renold manufacture. The double-acting damper was much the same as a Holroyd (later owned by Renold) patent from the 1950s.

As noted by Bryan, life expectancy is considerable, dependent only on regular gearbox oil changes and a magnetic plug to prevent gear fines from clogging the damper pistons.

The original was a proper Triplex chain. My understanding is that Renold stopped manufacturing this and at some stage AC Scotland fitted 3 single row chains in lieu. This led to disasters  - one row took the load and broke, following which the remaining rows continued to try and keep the machinery turning with the broken bits in the chaincase!

Following AC Scotland's demise, the Brian Angliss era  AC Cars at Brooklands re-designed the chainwheels to accommodate a 3/8inch pitch Triplex chain. Note, the larger 1/2inch pitch chain could not be fitted into the chaincase. The damper was unchanged. The Company had some made as spares. These worked well although they are somewhat noisier and the noise is at a higher frequency (due to the shorter chain pitch).

These spares were all sold. The ACOC through its then spares subsidiary Acedes Spares Ltd had ten more sets made.  These utilised all of the 3/8 pitch Renold chain recovered by Brian Eacott from AC's Brooklands stores and new chainwheels made to the same AC Brooklands drawings. These are a straight swap for the original setup, needing only a slight easing of the inside wall of the chaincase at  the gearbox input end and very careful alignment of the two chainwheels.

A few sets are still available through Brian Gilbart-Smith. Please contact him for availability and prices. 

[administrator]

Whoops - sorry - original was 7/16" (= 0.4375") and later replacement 3/8" as John says.  I didn't check the decimal to fraction conversion before writing the post!

As far as I know all the Thames Ditton cars and the early Scotland ones used this. 

The 3/8" was engineered after production stopped.

Barrie Bird produced an alternative conversion which used a Hyvo chain (no damper required) and I suspect some cars are still running on this, but when one failed a while ago Hyvo were unable to produce a replacement and there was no 'corporate memory' of the work.

When the chain stretches you get a very noticeable and unpleasant tramping under hard acceleration as the chain jumps the chainwheels.  Replacing it is an engine out job.  Your call whether you do it or not but I guess you have at least another 20 - 30K life in the original.  Premature failure can occur if the damper pistons seize due to gearbox fines, as noted by John. 

[IanBrown]

Hello,
What's the current solution for chain replacement and where can I get the parts?
Regards
Ian