Lotus Elan

Enlighten me about con rods?

PostPost by: vxah » Fri Apr 05, 2019 7:46 am

Thanks for your thoughts 2cams, machine shop are collecting the crank today to either polish or grind the big end journals. I have pretty much decided to buy new pistons to achieve 10.5 compression, not sure yet about the rods, could not find the ebay arrow set?
On another note, has anyone " adjusted" the timing chain oil spray jet? From looking at it it seems to me that on a normal pushrod lump it would indeed spray a jet of oil directly onto the chain as most engines do but, due to the TC re-arrangement of the chain it looks to me that the jet will miss the chain directly and just hit the front cover? Minor thing I know but it might help the longevity of the chain?
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PostPost by: 2cams70 » Fri Apr 05, 2019 8:26 am

vxah wrote:Thanks for your thoughts 2cams, machine shop are collecting the crank today to either polish or grind the big end journals. I have pretty much decided to buy new pistons to achieve 10.5 compression, not sure yet about the rods, could not find the ebay arrow set?
On another note, has anyone " adjusted" the timing chain oil spray jet? From looking at it it seems to me that on a normal pushrod lump it would indeed spray a jet of oil directly onto the chain as most engines do but, due to the TC re-arrangement of the chain it looks to me that the jet will miss the chain directly and just hit the front cover? Minor thing I know but it might help the longevity of the chain?


This is the arrow set of LTC rods. Note they are narrow journal:
https://www.ebay.co.uk/itm/Lotus-Twinca ... Sw2fRcOiRO

No need to worry about the oil spray jet. On a LTC a passageway in the backplate directs the oil to where it needs to go. These are the ones you need to be careful not to block when using gasket goo. I myself prefer to cut my own gaskets using high quality material rather than resorting to gasket goo.
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PostPost by: vxah » Fri Apr 05, 2019 8:54 am

Ah yes, need to study things more! Maybe if I had the casing here I would have spotted that?
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PostPost by: vxah » Wed Apr 10, 2019 1:15 pm

As my late father would say, measure twice cut once.. re-measured the chambers, 36cc! Seems Mr Stagg knew a thing or two!
I measured the volume with a piston 10mm down the bore giving me 56.5cc meaning the valve pockets equate to 2cc, with 1mm crushed gasket @5.4cc I worked out the static cr to be 10.1.. Not enough? If I use the 4.826" rods and machine the outer edge of the crown 0.026" I get the 2cc back giving me 10.6.. ? Perfection?
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PostPost by: types26/36 » Wed Apr 10, 2019 5:07 pm

vxah wrote: I measured the volume with a piston 10mm down the bore


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PostPost by: vxah » Wed Apr 10, 2019 5:36 pm

I did this so it would take into account the raised portion of the crown as well as the valve pockets, used a flat piece of Perspex as you would on a cylinder head cc check.
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PostPost by: 2cams70 » Thu Apr 11, 2019 6:27 am

The piston is not designed to be machined in that area. Only the intruder part is designed to be machined. Decreasing the distance between the first compression ring and the top of the piston will make the top ring run hotter and the piston may also be made weaker around the groove area. I'd check with the piston manufacturer first before doing any machining.
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