Timing chain for tall block

[bcmc33]

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,

You don't say in what car the tall block will be used.
Assuming the undecked 711M block is 11.5mm taller than the 701M block, it would certainly foul the bonnet in my Sprint.
So with the 82mm stroke you're aiming for 1750cc?
What cams are you using and what level of head porting?

Do you plan to get it on a dyno or rolling road to see what power/torque it has?

[Foxie]

="bcmc33

Sean,

You don't say in what car the tall block will be used.
Assuming the undecked 711M block is 11.5mm taller than the 701M block, it would certainly foul the bonnet in my Sprint.
So with the 82mm stroke you're aiming for 1750cc?
What cams are you using and what level of head porting?
Do you plan to get it on a dyno or rolling road to see what power/torque it has?

1971 +2S
I taper spacered the body to accomodate this when fitting the Spyder chassis. There's a cigarette paper's clearance between the cam cover and bonnet
83.5mm x 82mm = 1796cc
QED 420 head + 45 Webers
Found a dyno place here lately, hope to do a run maybe late September

New crankshft arrived to-day, departing for MSA Euroclassic 1st September

[CBUEB1771]

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.

Not decking the cylinder block is a preferred approach. When you take a lot of material off of the top of the block you bring the deck down very close to the coolant passages thereby weakening the cylinder block. Spending the money on long rods and saving the block is a good plan.

[Foxie]

Sean,

Assuming the undecked 711M block is 11.5mm taller than the 701M block, it would certainly foul the bonnet in my Sprint.

Brian,

You could do a little modification to the bonnet.
Would you really mind a genuine "Power Bulge"

[bcmc33]

Not decking the cylinder block is a preferred approach. When you take a lot of material off of the top of the block you bring the deck down very close to the coolant passages thereby weakening the cylinder block. Spending the money on long rods and saving the block is a good plan.

As I understand it, decking by 5mm is the absolute maximum before potential damage will occur.

[holywood3645]

I have posted a similar question at (link below), and need some sound advice before I proceed with this engine build.

elan-for-sale-f2/adjusting-valve-timing-engine-builders-second-question-t24260.html

The 711m block i am using has been decked, and is only 4mm taller than stock L block, (1600cc rods and crank) QED 1700 cc spec.

I have built the engine using a continuous 122 link chain. However, I feel the 122 link is providing too much slack even with the extended piston tensioner only providing correct tension at the max adjustment. During valve timing, I have experienced the valve train slip a tooth, if the tensioner is backed off slightly. I beleive this is because of the excess play and the amount of slack taken up by the chain tensioner.....This is very disconcerting for me. It is all sealed and buttoned up, head on etc. I really don't want to break the motor apart to change to a 120 link, however here my options:
1) Break the motor apart and replace the 122 link with a 120 continious link chain
2) Split Link 120 chain feed through the timing chest.
3) This is somthing I don't see posted or suggested here, but dont see why it can't be done.... Use a chain break similar to those used in go-karting or bikeing and remove 2 links, and reswage the link. (not sure if they are made for this size of chain) We have use this method in karting for over 10 years with motors that turn 15500 rpm
OR ???

Feedback and advice is very much appreciated as I'm dead in the water until i get this sorted out
James

[types26/36]

James,
As I have said previously I have built a couple of 711 decked motors and quite a few normal 1500 based motors, I usually use a chain with a split link and have never had a problem despite using them in mild competition back in the day.
I have at the moment another 711 engine that I really must get round to finishing but again I will use a split link chain when I assembly it.
The nay-sayers will tell you not to use the split link chain but as I have never had an issue I disregard this opinion, I also find it much easier to change cams/remove & ins the head etc. when using a split link....BUT FIT THE LINK THE CORRECT WAY ROUND
Pictured below is my Sprint engine which I am busy working on......note the split link.
ps. I am not sure you can fit a 120 link on a tall block although I don't ever recall trying

[elj221c]

There may be another way. When I bought my Elan the engine on an L block had been professionally by a well known engine builder of the day. It had a mixture of Cosworth and BRM bits and was built for sprinting. I do not know the reason why but it had an odd link in the chain, so presumably it was 121 links. The odd link was 'jiggled' so that the side plates on one end was on the ouside run of the chain, the other on the inside. I've never seen or heard of one since, mind.
When I built a tall block I used a 122 link chian with no mods at all to the cam drive components. Yes, the tensioner was screwed quite a long way in but there was never an issue with it. Obviously it will all depend on the rods and pistons as to how much the block is decked. In my case I used Cosworth forged pistons and the standard long rod that came with the block.

[bcmc33]

The 711m block i am using has been decked, and is only 4mm taller than stock L block, (1600cc rods and crank) QED 1700 cc spec.

James,

When I did my tall block I decked 5.75mm to bring the standard Twink pistons level with the block. The head was then made to suit a 10.5:1 CR with a 1mm thick gasket.
From what you say, your block has been decked 7.5mm. From my calculations this would bring a number of issues - one of them being a slack chain. Another thought is; are your pistons protruding above the block by 1.75mm?

When I did my block I took advice from an experienced tall-block builder and increased the 'nose' on the quadrant by 5mm. As I understood it, the 122 link chain is a little too long and additional adjustment is required to compensate. I silver soldered a piece of brass onto the end and trimmed it to shape. See picture

This extension (maybe 7.5mm in your case) coupled with the necessary longer plunger and spring should do the trick.

[holywood3645]

To answer the piston height question, I had a set of Omega Intruder forged pistons, that I had the intruder portion removed. The pistons sit flush with the top of the block at max stroke. Its an 83.5 bore, 711m crank rods, i calculate CR around 10.5 to 1.

I tried research the 121 link staggered chain, but found nothing except a few mentions on this board.

Thanks for the input..

James

[bcmc33]

To answer the piston height question, I had a set of Omega Intruder forged pistons, that I had the intruder portion removed. The pistons sit flush with the top of the block at max stroke. Its an 83.5 bore, 711m crank rods, i calculate CR around 10.5 to 1.

Are we to assume that you removed more than just the intruder to achieve the flush condition?
On my Twink with 83.25 Omega pistons I removed 3mm of the 6mm intrusion to achieve 10.5:1 CR.

[Tonyw]

I for one was expecting to see a plethora of posts against using a split link chain and was going to point out that I have used split links on many vehicles including TC's motorcycles and some of my daily drives and I have never experienced a problem with them as long at the are fitted correctly.

One obvious advantage is that you can feed a new chain in without any dismantling of the engine, you do need to be very careful of course and it helps to have a third or fourth hand when fitting new chain.


Tonyw

[holywood3645]

Brian, I only removed enough from the piston to acheive a flush deck condition. A correction, I have a 4.6mm timing chest spacer(not 4 as previously reported), and also installed a paper gasket for underneath (fitted on bottom between the timing chest and 4.6mm spacer) this brings it flush with the top of the block. A normal cork gasket was fitted on top before the head was put in place.

I have not had any issues with the water jacket as someone suggested. I cleaned the head bolt holes/threads out and ran a plug tap to the bottom of the thread.

I have resolved the chain slipping issue, (It was a stupid mistake on my part ) I still have a little concern about the chain length and the tensioner being almost at maximium insertion with the 122 chain.
BTW Dave Bean have a split link 121 chain that i purchased, but was going to stick with the 122 link inspite of the travel.

I now have everthing lined up (within 0.5 deg on the exhaust cam in error, and perfect on the inlet) while i would like to do the quadrant modification, I may pass on it. Just the idea of pulling it apart again, after all the trouble I have had really does not appeal to me...
I have posted a picture of the pistons and deck of the motor.

Still open to "must do" advice, including pulling the quantrent and silver soldering the extension piece. As I dont want to royaly 'F' this up after all this work.

James

[holywood3645]

BCMC33

Brian
I would have though the pad the piston tensioner pushes against would need extended toward the straight edge (RED in second picture). The top picture from BCMC33 post confuses me as it appears to lengthen the quadrant. Maybe just the angle is confusing

Can anyone add insight?

James

[bcmc33]

BCMC33

Brian
I would have though the pad the piston tensioner pushes against would need extended toward the straight edge (RED in second picture). The top picture from BCMC33 post confuses me as it appears to lengthen the quadrant. Maybe just the angle is confusing

Can anyone add insight?

James

James,

That's what my photo shows - it's just a poor view I guess. The photo was taken in the direction shown:

Chain%20tensioner%202.jpg (38.75 KiB) Viewed 1119 times