solid crank pulley good or bad?

Post by **picky** » Thu Jan 18, 2007 2:14 pm

I have seen several companies advertising a "solid" crank pulley as an upgrade to the old pressed one. The later 1275 engines have a crank pulley made out of two peices of steel, and a rubber ring inbetween the two, which I think is meant to absorb crankshaft vibrations. As the thin metal of the pressed steel pulley would also absorb vibrations a little, is a solid crank pulley a good idea? I am fitting a supercharger to a midget 1275 engine and I am making a crank pulley from aluminium which has provision for the modern "serpentine" 6 groove belt for the supercharger. If I make the pulley out of one piece am I going to be shortening the life of the crank? Minispares do this crank pulley which appears to be much more complex "friction damper" http://www.minispares.com/Product.aspx?pid=37369

Any ideas gratefully received!

Post by **Kevin** » Thu Jan 18, 2007 2:51 pm

Minispares do this crank pulley which appears to be much more complex "friction damper"

Well that looks a bit of kit and a half, but the price.......... still if its for a race engine the product is more important than the price I suppose.

As for the solid pulley`s that are on the market they must be made from a good quality steel if they are unbreakable.
So I am not sure that your choice of material is a good one, I think you may have to make contact with an engine builder who has done supercharged engines possibly someone from MG circles ?

Post by **picky** » Thu Jan 18, 2007 3:00 pm

I am sure that the solid steel damper itself is unbreakable, its whether it does the engine any good that I am worried about.

Post by **bmcecosse** » Thu Jan 18, 2007 7:25 pm

Aluminium will just rip over the key on the crank. You should use EN 24 - or maybe EN8 would do at a pinch. The vibration damper is there for a purpose - it definitely damps out vibrations !! I broke 2 948 cranks - then fitted a damper (from an early Morris 1100 engine) - result, no more broken cranks. But with a supercharger you will not be revving the engine - so you should be ok. Consider lightening and balancing the flywheel.

Post by **Dominic** » Thu Jan 18, 2007 8:03 pm

I broke 2 948 cranks

I misread that as 2,948 cranks... must have been hard keeping count!

Post by **bmcecosse** » Thu Jan 18, 2007 8:14 pm

It was bad enough at 2 . Had to wrap the broken cranks up in really oily paper and corrugated cardboard - and very carefully hand them in to the BMC parts place when collecting the 'exchange' crank. First time - the lad then took it - and threw it down behind him - so no wonder it was broken !! Second time - went to a very different BMC garage - and just ran away quick leaving the again well wrapped and disgustingly oily crank on the counter!!

Post by **minor_hickup** » Thu Jan 18, 2007 8:22 pm

Thats worse than me returning my valve spring compressor after sorting my exhaust valve!

Post by **bmcecosse** » Thu Jan 18, 2007 8:46 pm

That's the spirit!

Post by **Scott** » Thu Jan 18, 2007 10:39 pm

bmcecosse wrote:It was bad enough at 2 . Had to wrap the broken cranks up in really oily paper and corrugated cardboard - and very carefully hand them in to the BMC parts place when collecting the 'exchange' crank. First time - the lad then took it - and threw it down behind him - so no wonder it was broken !! Second time - went to a very different BMC garage - and just ran away quick leaving the again well wrapped and disgustingly oily crank on the counter!!

Classic !!!

Back on track......
Another issue with the pressed metal crank pulley is that the rivets become worn/loose. Eventually the pulley becomes loose & can fall apart.

Post by **bmcecosse** » Fri Jan 19, 2007 7:36 am

Only seems to happen with certain 'after-market' pulleys - for normal use I strongly suggest the proper crankshaft damper be used -but in this case I appreciate a special pulley to drive a s/charger is required.

Post by **picky** » Fri Jan 19, 2007 9:16 am

I have a big block of aliminium, and I have the damped type pulley from the midget engine. I am thinking if I split the midget pulley into its two pieces, and then machine the ali pulley, so that it can be bolted to the inner part of the midget pulley with bolts and rubber washers/spacers. This should hopefully add some damping "effect" and also means that the part that is in contact with the crank key is steel not ali. Only trouble is my piece of ali is 5 inches diameter and I dont think it will fit in the chuck of the lathe I am borrowing!!

Post by **bmcecosse** » Fri Jan 19, 2007 2:44 pm

Ahh - the original Mini carnk damper was a bolt-together thing. Quickly changed to the present bonded item - and it works. Your plan may work - although I am a bit dubious about the 'rubber washers ' !! I think it would be more likely to throw the crank out of balance than anything else. Maybe better to try the hub from one of these falling apart pulleys - and just fix the aluminum part to that - solidly. If you are not going over 6000 rpm - it will be fine. If the ally is too big - just rip lumps off it with a hack saw till you have a hex that will fit the lathe !

Post by **Kevin** » Fri Jan 19, 2007 3:10 pm

Only trouble is my piece of ali is 5 inches diameter and I dont think it will fit in the chuck of the lathe I am borrowing!!

If the ally is too big - just rip lumps off it with a hack saw till you have a hex that will fit the lathe !

Ask the borrowee if he has some reverse jaws for the chuck as they will have a larger capacity.

Post by **picky** » Fri Jan 19, 2007 5:00 pm

I dont think I explained the rubber washers in detail - I was thinking along the lines of several bolts with rubber parts so that it is held together securely enough. I had a power cut all afternoon today, which I spent seperating the standard bonded damper - took me ages. I think I will use the inner part of this and attach it to my aliminium bit.

I will see if the reverse jaws fit, although I suspect they dont.
Thanks for everyones input! manufacturing the ali part is going to take some time...

Post by **picky** » Mon Jan 22, 2007 11:29 am

Update: I have looked carefully at the kit you can buy to do this conversion and they use a solid aluminium pulley, MMOC user GAS has this conversion and has not had any issues with the crank keyway ripping the aliminium as bmc suggested might happen. Im going to use the inner part of the old crank pulley, so i dont have to machine the part that accepts the crank, and solidly attach this to my ali pulley.

It would be great to have all the rotating parts balanced, but I dont know anyone near me (yorkshire) that would do this?? Does anyone know approx cost of this aswell.

Post by **bmcecosse** » Tue Jan 23, 2007 7:42 am

Well - I have had the steel pulley work loose on the key - so I wouldn't fancy ally lasting too long! But if you use a steel centre section it should be fine. Balancing is not important unless going for over 6000 revs - which is not the aim with super or turbo charging - moderate revs with lots of torque is the name of that game ! But there is no harm in self balancing the rods and pistons - decent set of accurate scales can do it. They are the main 'out of balance' forces - banging up and down - so if you balance them it will make for a smoother engine.

Post by **picky** » Tue Jan 23, 2007 9:29 am

The lathe I am able to borrow is a big beast, I might even be able to get the flywheel on it, Im not sure as I have not seen it for a while. I would be able to lighten the flywheel but to balance it on a lathe? I think I would need some other equipment.

bmc, regarding the pistons and rods - if I select the lightest rod, and the smooth off the heavier ones with a grinding tool until they all weigh the same, and do this with the pistons also, is that what you had in mind?

The tuned 1098 I have at the moment has not had any balancing done, and I have to set the tickover quite high because the revs at tickover vary so much, so Im keen on this new engine being super smooth...

Post by **bmcecosse** » Tue Jan 23, 2007 10:42 am

Balancing does very little at idle - it's above 6k that you see a difference. My 1360 Mini engine is uper smooth to all kinds of revs!!
Yes - just match the rods and pistons as best you can. Ideally it's supposed to be an end-to-end balance too. But I doubt you want to take the pistons of the rods!! If machining the flywheel - set it up absolutely flat - so the tool is cutting all over the face before you start. This will ensure equal amount is removed all over. Also - don't machine too close to the ring gear - leave an untouched section there to reduce chances of it coming loose. In the past - we assembled flywheel and damper to crank - and set up two long straight lengths of silver steel absolutely horizontal - projecting from the flat bed of a drill machine. The crank was then sat on the bars - running on the mains - and allowed to roll as it wanted and so settle with the heavy section down. This was marked with chalk and repeated several times until it became obvious there was indeed a heavy point. Some holes were then drilled at that point - and the exercise repeated until the assembly showed no signs of settling in any particular point. This of course is only a 'static' balance - but it's better than nothing. And that engine ran and ran in a competition Mini for a long time without giving any undue trouble. If doing this you ned to mark the crank and flywheel to make sure it's always assembled same way on the crank - this is not a problem on a Mini - it can only go one way!!

Post by **picky** » Thu Feb 01, 2007 9:50 pm

thanks for the info bmc, could you explain "end to end" balance?? The pistons I have at the moment, one of them is different from the others.. so Im going to get another set that are all the same. Not sure if the flywheel will fit on the lathe, I am making the crank pulley tomorrow so I will check the depth of the lathe.

Post by **bmcecosse** » Thu Feb 01, 2007 10:02 pm

It' s just that - you pick a known balance point - that you can achieve precisely on all 4 rods (usually the joint where the end cap meets the main body of the rod - and you balance the rod on a knife edge at that point - and weigh each end, comparing them all with each other. Then you lighten the heavier ones until all 4 weigh the same. It's difficult to do - i tried it once and wasn't convinced - so after that I just went with overall weight! But the Pros would do the end to end thing.