Thoughts on keying intermediate shaft and pulleys?

[gmendoza]

I really dislike the design of the intermediate shaft and pulleys. Many engines failures have been caused by the slipping off the pulleys. So since I have my motor appart right now, I've been thinking about keying the intermediate shaft and intermediate shaft pulleys. I'd leave the cams alone.

What are your thoughts?

[Rgardner01]

I have no idea why they did not do this from the start. when I had my engine out I thought of the same thing....if the cams retain the move able then there is no need for movement on the bottom set that I can see. Let em know if you come up with a design or shop to cut the key ways.

[gmendoza]

The deed has been done. The shaft and pulleys were drilled and steel 3/16" dowel pin installed.

[lotus4s]

Nice work!

[Rgardner01]

NICE!!! Great job.

[gmendoza]

Thanks guys. One less thing to worry about.

[Günter]

so next on the list is two 'automatic tensioners' ..?

..and maybe some 'safer' fixings for the cam-pulleys, not really indexed/keyed ..but something that does not only relies on the 'clamping' force

[shawty_82]

What's the reasoning behind doing this?what does it prevent happening?

[Günter]

it is said that in the early days, some engines failed not only on the 'liner problems' (the thing with the weakenes of the sealing compount to the liner base on temperature changes ) -but also on getting lost of the screw and fixing plate (as seen in the pictures) that go into the intermediate shaft and clamp the intermediate belt pulleys there. So in fact if the screw was not thight and glued in additionall the pulleys could lost the position and would irritate the timing. ..with the logical effects on valves and pistons..

it happened for example on my engine as it was still relatively new and in previous owners hands.

[shawty_82]

Ok,so it basically means by doing this that the pulley is held in place prevented and from "slipping" on the intermediate shaft if the bolt isn't tight enough?is that right?

Would the bolt backing out not mean catastrophic piston/valve damage with this modification then?

[Günter]

Ok,so it basically means by doing this that the pulley is held in place prevented and from "slipping" on the intermediate shaft if the bolt isn't tight enough?is that right? ..

Right, that's all what it is for -as you can imagine ..if the puleys are not in the fixed position the timing between crank on the base and cams on the top is incorrect. You can place the intermediate pulleys in any position, as you position the cam pulleys in a corresponding order on engine rebuild .. so if you fix this problem there with the intermediates you have one 'problem zone' less to think about. the internal 'intermediate drive' is just a chain going from the crank up to this little shaft there that passes the front cover ..the oil-pump is also there inside in the front cover .. all the rest of the camshaft-drive is external, as what you see on the engine pictures -pretty simple, as long as all stays where it should

[shawty_82]

The proverbial penny has dropped, thanks muchly another thing to add to the 'to do' list once I'm an owner

Edited August 21, 2012 by Tim Shaw

[Günter]

if work was done well, aka 'use of right glue' as specified in *service bulletin* and clamped down in the right way it works so far on several engines, my own too .. so I see it more as one step to a fully rearangement of the external cam drive, as for example to add whide pulleys for less stress on the belts (as the type used is small) and I think if you change for corresponding bigger diameter the number of theeth in contact per time are also higher, so the load is spread more evenly in the time of contact for a specified area on the belt. And of course -some automatic tensioners would also be a cool thing to have ..and indexed cam pulleys, instead of the indexed cams (as the set-up hole in the cams can mean 'there is a weak point' in my mind ..)

[lotusespritse]

So is this something that could be done as an upgrade with the engine in the car?

It seems if you had a right angle drill, you could clamp down the camshafts and crank shaft, remove the bolt holding the intermediate pulley, drill just a shallow hole (maybe 1/8" to 1/4") between the seam of the shaft and pulley and put in a short piece of rod or a ball bearing and then put back the bolt. It wouldn't take much metal that is held captive by the bolt to keep the pulley from spinning on the shaft.

[Günter]

you could try it ..but mention that for the rear pulley you still would need the 'clamping' ..as the ball from an old ball bearing and held under the big head scrwew just fixes shaft & first pulley in your arrangement then !

[EspritV8Pilot]

Saw this first hand at Gonzalo's place. He is a very smart cookie. I'm gonna have him build my motor when the time comes.

[lotusespritse]

I don't see that Gonzalo keyed the pulley for the chain in the photos -- just the pulley for the belt. So the pulley for the chain is also known to come loose?

Reminds me of the Porsche 996 and 997.1 motor that has 4 fatal flaws in the design that can bite you at any time. Porsche left those flaws unchanged for 10 years of 911 and Boxster engines, so we can't be too hard on Lotus.

you could try it ..but mention that for the rear pulley you still would need the 'clamping' ..as the ball from an old ball bearing and held under the big head scrwew just fixes shaft & first pulley in your arrangement then !

[ramjet]

The method used above is called scotch keying. Usually uses a threaded grub screw as I have generally seen it used on interference fits where there is no retaining bolt to hold the pulley (or whatever) on.

As the pulleys on the cams have the retaining bolt and washer, this method of essentially a 'round' key is totally adequate.

Good work.

[Günter]

I don't see that Gonzalo keyed the pulley for the chain in the photos -- just the pulley for the belt. So the pulley for the chain is also known to come loose?

..oh dear, who said that !?

go out to your carm, look into the enginebay there on front of the engine, and undo the belt covers ..(or easier way, take a look into the workshop manual ..now!) -what you find is that the 918 does simply have two separate 4 cylinder engines in one block, with two(!) belts ..so there are two pulleys clamped onto the intermediate shaft (and as said, the chain sprocked drive thing is inside the engine, this does not run on the outside where the belt drive is .. )

[lotusespritse]

Oh, ok.

Guess you would need to drill a deep enough hole like Gonzalo did, or find a way to lock the 2 sprockets together and just key the first one.

[Günter]

no, as the four cam-pulleys are also not 'keyd' ...what means you can (on a rebuild for example) undo the intermediate drive system, give it over to machine-shop, get an conventional key groove done into intermediate shaft [square shape, as for ordinary lock keys] & into the intermediate pulleys , and ready to go .. you can reassemble the whole thing.

..the exact position in reference to the cam timing and tension is done via the four pulleys on top of the engine

[t70]

WOW!!! DO I LOVE THIS IDEA!!! I was floored when I was assembling Aerobat's engine and I realized how the system worked. I couldn't grasp how this could be done this way without any kind of keyway. I will be doing this on my engine for sure.

[Günter]

at least the crank pulley and the chain wheel on the crank are keyed ..

we can only wounder why, as Lotus thought it can go without on the cam drive anyway

(just joking ..for now, knock on wood)

[Dave Hopwood]

Mine has just failed, the bolt worked loose and trashed the engine

I can't believe Lotus didn't include a key in the design

I won't dream of fitting the engine back without this mod

Dave

[Günter]

Scott:  ..you are right in some ways, as the bolt (if it sits all tight there) should hold it  

 

-thing is there are different materials fitted together

 

-the 4 cam wheels and those 2 intermediate wheels lower down are made from anodized alloy, whereas the intermediate chain drive and sproket is steel

-so if you tighten it as per specification, but the material quality of the alloy on those two intermediate wheels clamped together on the intermediate shaft gets soft or 'settles' over time/heat cycles, you could end up with a loose package, where the steel bolt is still glued into the intermediate shaft (or fixed into position with your idea of an wire/metal strap)  ..and the alloy timing belt wheels there are spinning loose and running out of orientation

 

-so to fix those alloy wheels into position, relatively to the intermediate shaft, this is a more permanent way

 

 

..the question still is how to adress the upper four wheels in relation to the exact timing (and possibly required reposition over time)

Edited November 26, 2013 by Günter