36 replies to this topic

[Guess-Works.com]

or MED

 

http://www.med-engin...ssembly/pulleys

[nicklouse]

thats a better price.

 

but still next months shopping list.

[Earwax]

More of a interest point rather than assistance to nick.... 

 

from what i recall the swiftune race engines ( dc5 crank or whatever) were recently running NIL damper..... ( ie none) again i thought i had seen that previously most of their built engines sported the KAD heavy ones but Swiftune were thinking of developing their own and so at last years mid ohio races - the car piloted by nick swift went damperless...... again no one suggested this was the answer for hi revs,,,more of a state of not sure what to fit

 

the romac and med ones both seem good in use with standard type cranks  with a couple of med ones ( a year or so ago now, being too tight a fit without a tiny linish)..... although longevity is the question for racers.... it seems the elastmer/rubber/or plate don't last a lifetime, but we would hope for a few seasons

 

the mechanical you beaut ones produced by ATI - (nascar engines running them)would be wonderful if designed for our little motors but alas no volume no investment/return..... 

[spiguy]

My apologies for jumping in here to ask a question, however reading this made me go off and read about the purpose of the damper. That then made me wonder how you can tell if your pulley/damper would benefit from replacement? Is the sort of vibration that you would feel from the engine if this is in poor condition, very noticeable - ie distinguishable from 'normal' vibration levels ?  I have never changed the pulley before, and hadn't appreciated that it could wear out.

 

Thanks in advance.

Edited by carlukemini, 20 April 2015 - 11:11 AM.

[Spider]

Not usually. On some cars (notably 6 cylinders) they usually knock when they have failed, but on our cars the outer 'spins' a few degrees relitive to the inner. I scribe a good heavy line across the inner and outer so a visual inspection (with a mirror) will show if it has failed.

 

Very important device and one I feel not properly understood, often over looked.

 

After all it's only a 'pulley', isn't it!

 

Bhaahahaha,,,,,,,,

 

Most busted 998, 1100 and in particular 1275 cranks I've seen have been from failed dampers.

[nicklouse]

My apologies for jumping in here to ask a question, however reading this made me go off and read about the purpose of the damper. That then made me wonder how you can tell if your pulley/damper would benefit from replacement? Is the sort of vibration that you would feel from the engine if this is in poor condition, very noticeable - ie distinguishable from 'normal' vibration levels ?  I have never changed the pulley before, and hadn't appreciated that it could wear out.
 
Thanks in advance.

I will take a picture of the back of mine so you can see where it fails.
 

 

Not usually. On some cars (notably 6 cylinders) they usually knock when they have failed, but on our cars the outer 'spins' a few degrees relitive to the inner. I scribe a good heavy line across the inner and outer so a visual inspection (with a mirror) will show if it has failed.
 
Very important device and one I feel not properly understood, often over looked.
 
After all it's only a 'pulley', isn't it!
 
Bhaahahaha,,,,,,,,
 
Most busted 998, 1100 and in particular 1275 cranks I've seen have been from failed dampers.

and this is where people lose it as the damper is not the pulley. but a mass that has been bonded to the pully. or if an S type bonded to a carrier and then bolted to the pulley.

[spiguy]

Thanks Moke. So am I right in thinking that if you were to replace this, that you could do so simply by purhasing and fitting a new replacement pulley / damper ? I see minispares do a standard one piece unit, and I also looked at the ones linked in this thread. Is it just a case of off with the old pulley with the engine in situ, and on with the new one? 

[spiguy]

Thanks Nick.

[Spider]

Thanks Moke. So am I right in thinking that if you were to replace this, that you could do so simply by purhasing and fitting a new replacement pulley / damper ? I see minispares do a standard one piece unit, and I also looked at the ones linked in this thread. Is it just a case of off with the old pulley with the engine in situ, and on with the new one? 

 

For stock or mildly tuned engines, I'll say a cautious yes.

 

On higher reving / higher torque engines, they really need more of a damper tuned to higher hamonics. It really is a very complex subject though. I'll also add that lightening the bottom end, particularly reciprocating parts but also spinning bits helps push the harmonic resonant frequecies higher and (hopefully) out of the rev range of the engine.

 

Roughly on stock 1275's revs to be careful of are (from memory) around 3 000, 6 000 and 9 000, with those at the upper end (of the rpms) being worse than the lower end, not just because of the speed it's all spinning at but more so because of harmonic resonance. Yes, and that may come across as (someone recently put it) scientific mumbo jumbo, however, have a look at the busted cranks from these engine, funny thing is, they nearly all break in the same place (between the No. 2 Big End and the Centre Main). Co-incidence, mumbo jumbo, not enough fillet radius - in the same place?  MMMmmmmm,,,, don't think so,,,,,

 

This is also why the early cooper S had a different damper - tuned for a different engine!

 

850's & 998's can often get away without a damper, but start pushing some HPs through them and that changes. remember HPs is a factor of torque and speed,,,,, If you are only going to spin them at high revs, then a damper is almost a waste of money.

 

It's only a 'pulley' after all

Edited by Moke Spider, 20 April 2015 - 12:25 PM.

[nicklouse]

Thanks Moke. So am I right in thinking that if you were to replace this, that you could do so simply by purhasing and fitting a new replacement pulley / damper ? I see minispares do a standard one piece unit, and I also looked at the ones linked in this thread. Is it just a case of off with the old pulley with the engine in situ, and on with the new one?

basically yes. BUT as i mentioned above there is the S type where the pulley and damper are seperate these need balancing together. there is normally a warning on the sellers pages about the need to balance parts.

but saying that many come ready to just fit.

when changing it things to consider. Rad out. the oil seal might need replacing. (timing cover off)....

also best to do it in a "clean" area as you are opening up the engine.

[spiguy]

Thanks guys. Sorry for my ignorance, but are you saying that the timing cover is removed to get the bottom pulley off? And by oil seal do you mean the crank oil seal? is this all doable in situ?

 

last question - based on reservations about the standard damper (minispares also make similar comments) is it better to go for the 'S' or maybe even the KAD one linked earlier in this thread ?

 

Thanks again for the info and sorry for diverting the thread this way, I just thought it would be easier to get your attentions by replying in this thread rather than starting a new one !

[nicklouse]

just to change the pulley the timming cover does not come off.

the KAD one.mmm depends on use. it is big and heavy but will be very good at doing what it does where an engine is doing constant revs for a prolonged time if those revs are in the "danger" range.

[spiguy]

Hmmm.. so what would be best for a road car which just gets used for normal driving and a good hard drive once a month on club runs?

 

Maybe I will try to have a look at my current one, maybe I can make some marks as Moke described to see if inner and outer are still well joined.

 

I have no reason to suspect any issues (although the car is noisiest in the cabin at just over 3000RPM..) but now that I have read this, I wonder !

 

Thanks

[nicklouse]

i would just use a standard one.

[carbon]

More of a interest point rather than assistance to nick.... 

 

from what i recall the swiftune race engines ( dc5 crank or whatever) were recently running NIL damper..... ( ie none) again i thought i had seen that previously most of their built engines sported the KAD heavy ones but Swiftune were thinking of developing their own and so at last years mid ohio races - the car piloted by nick swift went damperless...... again no one suggested this was the answer for hi revs,,,more of a state of not sure what to fit

 

the romac and med ones both seem good in use with standard type cranks  with a couple of med ones ( a year or so ago now, being too tight a fit without a tiny linish)..... although longevity is the question for racers.... it seems the elastmer/rubber/or plate don't last a lifetime, but we would hope for a few seasons

 

the mechanical you beaut ones produced by ATI - (nascar engines running them)would be wonderful if designed for our little motors but alas no volume no investment/return..... 

 

If the crank does not have a resonance that coincides with engine's power band then you should be able to run without a damper. The problems happen when they coincide.

 

I am curious to know if anyone knows of 1275 engine dyno tests taken on identical engine with/without crank damper, I will post this as a separate thread.