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Crank Damper For Ribbed Belt Pulley

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#1 BaronVonchesto

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Posted 01 May 2024 - 04:38 AM

I was doing research on 1098 engines as I'm considering a 1098 build for a new project. It has come to my attention that our beloved A-series engines require a damper for the crank and that the damper is part of the crank pulley.

 

Some months back I changed my 998 A+ crank pulley from the regular one to a custom machined pulley for ribbed belts as I was so sick of the unresolvable belt squeal issues I was facing when running the air conditioning. I've been very happy ever since, but now I'm worried that I'm running an engine without a crank damper.

 

Are there any options for crank dampers that can be used with Ribbed belt pulleys? I know the later MPi engines used ribbed belts, and if I do go ahead with a 1098 build I would absolutely need a damper, and would prefer to stick to ribbed belts. Would the eye wateringly expensive KAD damper work with a Ribbed belt pulley?



#2 BaronVonchesto

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Posted 03 May 2024 - 03:11 PM

just bumping this up for attention



#3 DeadSquare

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Posted 03 May 2024 - 03:27 PM

How wide is your ribbed belt ?



#4 BaronVonchesto

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Posted 04 May 2024 - 11:58 AM

How wide is your ribbed belt ?

 

I don't have the measurement on me, but I believe its identical to the mpi belt



#5 PeterG

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Posted 04 May 2024 - 12:44 PM

Not sure if this is helpful. I installed the MPI pulley system on what was an SPI engine, now 1380 HIF44. The crank pulley and damper are one piece. The only mod to make it all work was to file back the water pump boss for the alternator mount by 0.14", and use the correct length belt with the same number of ribs as the MPI just a different length that adjusts up the same way as the V belt.



#6 BaronVonchesto

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Posted 04 May 2024 - 01:25 PM

Not sure if this is helpful. I installed the MPI pulley system on what was an SPI engine, now 1380 HIF44. The crank pulley and damper are one piece. The only mod to make it all work was to file back the water pump boss for the alternator mount by 0.14", and use the correct length belt with the same number of ribs as the MPI just a different length that adjusts up the same way as the V belt.

 

Indeed the facotry crank pulleys function as a damper, though fresh MPi pulleys are hard to come by. Mine was a custom machined one. It is quite common for people here to machine out of aluminium the pulley as a conversion, but I highly doubt it acts as a damper in any way.


Edited by BaronVonchesto, 04 May 2024 - 01:25 PM.


#7 BaronVonchesto

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Posted 04 May 2024 - 01:28 PM

or I wonder whether this would do the trick? 

https://minispares.c...lts/12A367.aspx

 

for what its worth I had my current engine dynamically balanced for up to 10k rpm. So would that mean running it without a crank damper would be okay?



#8 DeadSquare

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Posted 04 May 2024 - 01:57 PM

Even with a damper, 1098 cranks weren't happy  around 5500 RPM.

 

I have seen competition 1098 Spridgets with a larger diameter 997 cooper, disk type of damper, but the larger diameter might not fit a Mini front engine mounting.



#9 BaronVonchesto

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Posted 06 May 2024 - 09:20 AM

the consensus on the forums seems to be that the rpm limit of 1098s is 6000rpm.

 

I don't expect to need to drive for extended perioeds above 5k rpm, even on hill climbs, especially since the 1098 would have a larger displacement than my current 998.

However, even at regular speeds of 3-4k rpm, I think a dampner would be all the more crucial on a 1098 vs a 998 no? What sort could I fit to a crank pulley thats meant for ribbed belts?



#10 DeadSquare

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Posted 06 May 2024 - 09:43 PM

What is the gap between your ribbed belt and the timing chain case ?

 

This is where a harmonic damper will have to go.

 

From what I can remember of the racing Spridget, it was about a 7" disk, cut from 1/2" steel.

 

If there is room, something like that attached to your pulley with countersunk screws, might be possible.

 

To be any real use, a damper needs to be tuned to dampen the offending frequency.

 

No, I don't know how to do that.



#11 BaronVonchesto

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Posted 07 May 2024 - 12:08 AM

i shall try and take a measurement when i get the chance



#12 BaronVonchesto

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Posted 20 May 2024 - 09:00 AM

actually, coming back to this topic, how exactly does a damper function? From what I saw on MED's youtube they balance the damper, pulley and crank together.

 

When rebuilding my engine, I had the pulley custom milled from aluminium, and the whole setup was dynamically balanced to 11000 rpm. Crank + pulley + pistons + flywheel etc. The whole rotating assembly was balanced as a unit. In that case wouldnt the vibrations have already been tuned out?



#13 KTS

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Posted 20 May 2024 - 09:55 AM

balancing the pulley just means it doesn't introduce and new vibrations into the system when it's spinning - dampers and damping is all about dealing with the torsional twisting that combustion events place on the crankshaft

 

https://en.wikipedia...Harmonic_damper







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