Duplex or Simplex with tensioner for modded 1098

[bluegrass]

Hi,

Is it best to fit a Duplex timing chain kit, or Simplex with tensioner for a modded 1098 with standard cam,
Hif38, and 940 (small valve) head?

Thanks

[bmcecosse]

If you can scavenge the parts from a Mini engine - then the tensioner system will be fine. But it's uneconomic to buy all new parts - so just get the duplex which seems to be reasonably priced these days - although not sure about quality of some of the cheaper sets...

[les]

I'm thinking the quality of the sprockets is suspect, I say this because the original cooper s duplex cam sprocket and crank sprocket had numbers on them and were extremely expensive, admittedly a long time ago but can't see how the same items could cost so much less now.

[bluegrass]

ok , thanks.

I'm also need to get one for my 1275 midget engine build
with ACDodd cam. It needs 106 degree adjustment at TDC, so
would I need an adjustable duplex for that?

Thanks

[bmcecosse]

If you really want to do that - you will need an adjustable timing gear set - uber expensive. Frankly - if it's been correctly ground -it should give that setting with dot to dot setting. And even if it is a tiny amount out - it really won't matter for your intended use. For full race engines -the cam timing needs to be set up using a rolling road - it's not possible to just blandly say '106' degrees and know for sure that is the 'best' setting for your engine. Slightly more advance may give a tin y bit more top end power - and lose low down 'torque' and vice versa of course. If you feel you can measure the timing accurately enough (two clock gauges) and are prepared to make repeated measurements (because each cam lobe may give slightly different readings) you can fiddle about with 'offset' keys - but honestly - it's a high unsatisfactory business and really not worth the effort.

[bluegrass]

I'm glad you said that Roy....its been worrying me.
I'll just go dot to dot and use standard duplex.
I'll be stripping the 1275 engine in a day or so and posting
up pictures. I'll let you know what the head is (big valve or standard etc.)
Thanks

[philthehill]

Here is a NOS genuine Cooper S steel duplex camshaft pulley with the correct cast numbers and at a reasonable price as well.

http://www.ebay.co.uk/itm/Duplex-Timing ... SwmmxW4FW7

Unless you want to get the utmost out of the engine a standard duplex timing chain set up will suffice but saying that - with a re-ground camshaft the lobe profile may be out of sinc with the woodruff key slot so it may be better to fit an adjustable vernier timing chain set up to get the camshaft base timing correct.
Phil

[bluegrass]

Thanks for that...
Will this cooper camshaft pulley be ok on my midget 1275 ...will the timing work etc

[philthehill]

The Cooper S cam sprocket in the listing above is a straight fit and will require no alterations or modifications.
The timing marks are positioned exactly the same.
The Cooper S duplex steel crankshaft sprocket (Pt No: AEA695) is no longer available but a non steel (cast iron) replacement (Pt No: 12G1699) is available from the usual suppliers.
Phil

[bluegrass]

Thats lucky I just bought it. I need the duplex for two cars, so if there are any problems with the ACDodd cam timing, which would surprise me, I can just use it on the 1098 with standard cam. Thanks for the link

[philthehill]

Well done.
Phil