DIY Si
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| posted on 12/5/14 at 10:32 AM |
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Cutting down a crank damper/pulley
Morning all. In an effort to gain as much clearance as I can for my V6 in my Sprite, I am looking at cutting down the crank pulley. It's
designed to run two multi V belts, but I will only need the one. The problem I have is that the harmonic damper is the outer section of the pulley,
and since it's a high-ish revving engine, I don't really want to run without one.
But I'm struggling to think of a way round the problem. All the V6's used the same size pulley, so I don't know of any off the shelf
options. Can anyone think of a solution other than trying to find a crank pulley that matches from somewhere?
“Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.”
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
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scutter
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| posted on 12/5/14 at 11:23 AM |
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Si,
What state is your engine build at?
Could the bottom end be balanced after the pulley has been cut down?
Regards Dan.
The less I worked, the more i liked it.
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JAG
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| posted on 12/5/14 at 11:28 AM |
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Sorry Dan but Harmonic dampers don't compensate for a static out-of-balance - which is all balancing the bottom end will reduce.
Harmonic dampers are there to reduce the dynamic torsional vibrations caused by the combination of internal combustion, crank design and other loads
such as alternator, water pump etc....
I can't think of a solution that wouldn't require large amounts of engineering expertise and time.
[Edited on 12/5/14 by JAG]
Justin
Who is this super hero? Sarge? ...No.
Rosemary, the telephone operator? ...No.
Penry, the mild-mannered janitor? ...Could be!
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scutter
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| posted on 12/5/14 at 11:34 AM |
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Cool, just a thought. 
ATB Dan.
The less I worked, the more i liked it.
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tegwin
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| posted on 12/5/14 at 12:01 PM |
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Got any photos?
Is it possible to reverse the pulley and machine off the non useful bit?
------------------------------------------------------------------------------------------------------------------------
Would the last person who leaves the country please switch off the lights and close the door!
www.verticalhorizonsmedia.tv
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loggyboy
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| posted on 12/5/14 at 12:42 PM |
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I got my twin pulley C20XE one machined down to suit fitting in the Nova, it retained the harmonic rubber with no issues machnining it or running with
it for several years.
Mistral Motorsport
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DIY Si
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| posted on 12/5/14 at 01:05 PM |
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quote:
Originally posted by tegwin
Got any photos?
Is it possible to reverse the pulley and machine off the non useful bit?
Whilst this is the later pulley with the 36-1 trigger wheel, mines the same size as this. The mounting bit is virtually all behind the front section,
which is the harmonic section, annoyingly.
“Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.”
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
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mark chandler
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| posted on 12/5/14 at 05:24 PM |
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Given that the damping element is designed for an engine that you would expect to cover 200,000 miles if you lose it does it really matter in a car
that in reality will cover less than 10% of this?
You are also not running Aircon, power steering etc so this aspect is diminished, None of the cars of my youth including v6 fords and v8 rovers had a
dampened pulley or a dual mass flywheel either.
If it is carrying counterbalancing rates then it's a different matter, I would get out the saw and chop that lump off the front then clean up
with a lathe if possible, if not an angle grinder.
[Edited on 12/5/14 by mark chandler]
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clairetoo
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| posted on 12/5/14 at 05:36 PM |
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've been running alloy pullies on V6's for years - and plenty of miles - with no problems at all .
And I only rev mine to 8000................
Its cuz I is blond , innit
Claire xx
Will weld for food......
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DIY Si
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| posted on 13/5/14 at 07:46 AM |
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quote:
Originally posted by clairetoo
've been running alloy pullies on V6's for years - and plenty of miles - with no problems at all .
And I only rev mine to 8000................
I thought you blew your last engine up in the Fury?! And whilst this engine will only go to 8,000rpm, the next one I build will go higher so I need to
know the solution works before I build an expensive engine up.
Don't get me wrong, if there's a safe way to run without it, then all well and good. But if there's a sensible option for running
with one, then I would much rather do so.
“Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.”
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
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The Black Flash
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| posted on 13/5/14 at 10:25 AM |
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If you do, you'll definately need a full rotating assembly rebalance - the crank pulley on the Alfa is part of the balancing for the bottom end
- it's externally balanced using the pulley and the flywheel....
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The Black Flash
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| posted on 13/5/14 at 10:25 AM |
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dual post sorry
[Edited on 13/5/14 by The Black Flash]
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clairetoo
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| posted on 13/5/14 at 03:53 PM |
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quote:
Originally posted by DIY Si
quote:
Originally posted by clairetoo
've been running alloy pullies on V6's for years - and plenty of miles - with no problems at all .
And I only rev mine to 8000................
I thought you blew your last engine up in the Fury?! And whilst this engine will only go to 8,000rpm, the next one I build will go higher so I need to
know the solution works before I build an expensive engine up.
Don't get me wrong, if there's a safe way to run without it, then all well and good. But if there's a sensible option for running
with one, then I would much rather do so.
I didnt blow it up - the cam belt failed on starup , but the belt came with the ebay engine , so no idea how many miles it had done.......I did at
least 20000 miles with the alloy pulley set on it , as well as a 7lb alloy flywheel - if the damper was really needed , surely something major like
the crank would have broken ?
Its cuz I is blond , innit
Claire xx
Will weld for food......
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coyoteboy
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| posted on 14/5/14 at 12:46 PM |
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quote:
You are also not running Aircon, power steering etc so this aspect is diminished, None of the cars of my youth including v6 fords and v8 rovers had a
dampened pulley or a dual mass flywheel either.
Indeed. and likewise they were not designed (optimised, material reduced etc) with the knowledge that it would be present. You can't use the
"it was never necessary on old engines" excuse to remove features from a newer one. Nor can you assume that it's a fatigue life
problem and assume low miles is going to save you.
The way you'd need to address this is to do a custom one - you could make a half decent stab at it by testing and identifying the:
rotational inertia of the inner and outer parts as they are.
The stiffness and damping properties of the rubber.
Then trying to reproduce the effective damping coefficient and masses/spring effect with your own short design. Not impossible but not easy. Try not
to assume a similar one from another engine might work - it might, or it might resonate!
[Edited on 14/5/14 by coyoteboy]
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DIY Si
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| posted on 15/5/14 at 09:01 AM |
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Mmmm, this sounds like it'll be much more involved than I had imagined. Since this engine is going to be more of a test bed than the finished
article, I may have to run without the damper for now and see how I get on.
“Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.”
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
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Rocket_Rabbit
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| posted on 16/7/14 at 03:46 PM |
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I ran my old B18C-R engine with solid alloy pulleys and that was revving to 8800rpm. No problem despite the engine being 40k miles old and me putting
on 10k of hard miles on it. I plan to run one on my F20C too.
I did have a discussion with an engineer about the dampers. My argument was that since there was a rubber belt on the end, surely that would do the
dampening?
He said that the higher the revs, the less the effect the damper would have.
Run the belt as slack as you can, but I think a lot of this is manufacturers covering their arse.
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whitestu
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| posted on 16/7/14 at 03:53 PM |
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I welded a trigger wheel onto the one on my Zetec with no apparent ill effects.
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ashg
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| posted on 16/7/14 at 09:42 PM |
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just machine it down it will be fine. just think of the stress and vibration on the crank when you raise the clutch change gear accelerate hard.
that little pulley is a drop in the ocean and as said the mileage a kit car does its not worth over thinking.
Anything With Tits or Wheels Will cost you MONEY!!
Haynes Roadster (Finished)
Exocet (Finished & Sold)
New Project (Started)
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coyoteboy
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| posted on 17/7/14 at 12:13 PM |
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They're there for a reason, if you don't understand the finer details of why they're there and what happens when you remove them
you're risking failure. If you can't quantify that risk, you just have to accept that your crank is a consumable - this may be acceptable
to you and that's fine. I have SEEN with my own eyes forged cranks that have failed after a few K miles of not having a proper damper (please
people, stop calling it dampening - we're not making things wet here). It's there to reduce and/or remove torsional oscillation at natural
frequencies of the crank. These could be SIGNIFICANTLY higher than the clutch loading and confined to a small area of the crank.
The pulley isn't the load ashg, nor the stuff on the belt. It's there to remove oscillations within the crank caused by the accelerations
induced by the pistons during acceleration. The very thing you're claiming must be bigger than this drop in the ocean IS this problem. The
combination of clockwise and anticlockwise torque pulses generated by compression and power strokes, which occur at different frequencies as the RPM
change and can meet natural frequencies of the crank components.
Sure, you might be fine. I know how much I know about the subject and how much I don't know, and I wouldn't risk it on my
"engine's a consumable" tin-top. Your call.
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loggyboy
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| posted on 17/7/14 at 12:48 PM |
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If the damper is only on the outer pulley and only the inner pully is being used (I assume to drive what would have been driven as standard) then
surely removing it is not an issue as the items that were being damp(en)ed :p are no longer present.
And if I read the above right, it being there to damp the crank, not the items on the pulley, then why would it only have the damper on the outer
pulley not on both?
Mistral Motorsport
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coyoteboy
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| posted on 17/7/14 at 02:02 PM |
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Read up on tuned mass dampers. When they design it, it's designed with a specific rotational inertia and damping (rubber hysteresis and
springyness). If they don't want the mass of both pulley surfaces being in the mix they don't use it. It's not a
one-solution-fits-all. Same way you don't just look at suspension dampers thinking "if you need damping, I'll just turn it onto
max".
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coyoteboy
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| posted on 17/7/14 at 02:08 PM |
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For a brief read:
http://www.vibromech.com/customer/presentation/VESL-Full%20Scope%20Supplier%2020-Nov-06.pdf
and
http://www.dragzine.com/tech-stories/why-torsional-dampers-are-crucial-to-the-health-of-your-engine/
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Andy S
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| posted on 18/7/14 at 06:01 AM |
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quote:
Originally posted by mark chandler
You are also not running Aircon, power steering etc so this aspect is diminished, None of the cars of my youth including v6 fords and v8 rovers had a
dampened pulley or a dual mass flywheel either.
[Edited on 12/5/14 by mark chandler]
The Rover V8 had a damper from the off. - Not much of one granted but they got gradually bigger as the pulley loads were increased.
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sickbag
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| posted on 18/7/14 at 08:03 AM |
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I thought these dampers were only to help reduce the shock to the drive belts when a sudden load was applied from things like the aircon pump, etc.
Is this not the case then?
Finally back on the job!
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