Timing chain for tall block

[fjbm]

I'm going to build a 1661cc engine based on a 711m block, its crank and rods, but keeping the std. twincam pistons.

Which timing chain should I consider? The 121 or 122 link chain?

Thanks

[Foxie]

I'm going to build a 1661cc engine based on a 711m block, its crank and rods, but keeping the std. twincam pistons.

Which timing chain should I consider? The 121 or 122 link

122. An even number.

How could a Lotus type timing chain have an odd number of links

[billwill]

I'm going to build a 1661cc engine based on a 711m block, its crank and rods, but keeping the std. twincam pistons.

Which timing chain should I consider? The 121 or 122 link

122. An even number.

How could a Lotus type timing chain have an odd number of links

In an odd chain, one of the links is cranked. i.e it is an outer at one end of the link and an inner at the other end.


Whether they can be used as a twin cam timing chain, I know not.

[john.p.clegg]

I had an odd number chain made up for me at Newark and has been good for the past ten years...

John

[Foxie]

In an odd chain, one of the links is cranked. i.e it is an outer at one end of the link and an inner at the other end.


Whether they can be used as a twin cam timing chain, I know not.

Yes, that makes sense. I didn't know such a possibility was available.

[AussieJohn]

You can use a standard chain if you modify the bracket that holds the tensioner wheel.

[fjbm]

You can use a standard chain if you modify the bracket that holds the tensioner wheel.

Could you please explain how?

Thanks

[bcmc33]

I don't think you really need the extra two links, but it is the most usual and convenient method - that's why the usual suspects sell the 122 link chain.
What you do need is the longer plunger to take-up the extra slack. I was also advised by an experienced tall block builder to extend the nose on the quadrant where the plunger presses by about 5mm.

I hope this helps.

[AussieJohn]

If you cut the bronze bracket and braze it at a different angle it allows you to use a standard chain. I haven't done one for 30 years so I don't have any dimensions. This mod leaves the tensioning setup still working in the same parameters with no changes needed to the plunger etc. cheers, John.

[Foxie]

What you do need is the longer plunger to take-up the extra slack. I was also advised by an experienced tall block builder to extend the nose on the quadrant where the plunger presses by about 5mm

I don't understand how a tall block can result in extra slack in the standard chain. Surely the additional height will mean the chain is stretched rather than slackened ?

Will the standard chain fit on the tall block even with the tensioner fully retracted ?

I've had to fit spacing washers on the tensioner main nut to back it off on my tall block with a 122 link chain

[bcmc33]

What you do need is the longer plunger to take-up the extra slack. I was also advised by an experienced tall block builder to extend the nose on the quadrant where the plunger presses by about 5mm

I don't understand how a tall block can result in extra slack in the standard chain. Surely the additional height will mean the chain is stretched rather than slackened ?

Will the standard chain fit on the tall block even with the tensioner fully retracted ?

I've had to fit spacing washers on the tensioner main nut to back it off on my tall block with a 122 link chain

I'm simply working to information given to me by experienced tall-block builders. But logic says that there will be a lot more slack in the 122 link chain compared to the 120 link chain.
With the block at about 6mm taller and the chain being 19mm longer then there is about a 7mm length of slack to cope with over and above that of a standard chain. Hence the longer plunger that the usual suspects sell.

[Foxie]

Brian,

I think we may be talking at cross puposes here. My original question was in reply to your post 9th August that a standard chain could be used on a tall block. However there are tall blocks and tall blocks. I see in your last post (below) you quote the tall block as being 6mm taller. If this is so, this block would have been decked, as the unmodified tall block is 12.5mm taller than the Lotus block. I did not deck my tall block, but ordered longer rods to give the correct piston height, and also machined the (Omega) piston domes to get the compression ratio I wanted. So I not only have to use a 122 link chain, but also shim out the adjuster.

If the timing chain was vertical, you would have an extra 19mm as you say, but as it is angled at 73 and 80 degs, there is a cosine correction of about 5mm required

I'm simply working to information given to me by experienced tall-block builders. But logic says that there will be a lot more slack in the 122 link chain compared to the 120 link chain.
With the block at about 6mm taller and the chain being 19mm longer then there is about a 7mm length of slack to cope with over and above that of a standard chain. Hence the longer plunger that the usual suspects sell.

[AussieJohn]

Sean, I've never heard of a longstroke being built without lowering the deck height, [ I learn something new every day! ]. Is this an Irish way of doing it or is it widespread? cheers, John.

[bcmc33]

Brian,

I think we may be talking at cross puposes here. My original question was in reply to your post 9th August that a standard chain could be used on a tall block. However there are tall blocks and tall blocks. I see in your last post (below) you quote the tall block as being 6mm taller. If this is so, this block would have been decked, as the unmodified tall block is 12.5mm taller than the Lotus block. I did not deck my tall block, but ordered longer rods to give the correct piston height, and also machined the (Omega) piston domes to get the compression ratio I wanted

OK Sean, I see what you're doing.
However, I cannot see the any advantage in having longer conrods instead of decking the block - please explain.
Maybe I'm wrong, but I'm sure I would have a problem with the bonnet shut height with an undecked block.

[Foxie]

John, Brian,

I um, er, forgot to say I'm using an 82mm crank. I had to use longer rods than what I originally planned as on the test build the c/s counter weights were contacting the piston skirts around BDC .

So the full tall block height was useful

Sean, I've never heard of a longstroke being built without lowering the deck height, [ I learn something new every day! ]. Is this an Irish way of doing it or is it widespread? cheers, John.