Jump to content
Click here if you are having website access problems ×

Lightweight pulley

Tight fart

Recommended Posts

And this is a noticeable Improvement?

Manufacturers often use "heavy" crankshaft pulleys for Harmonic Balance purposes.. there are Two ends of a Crankshaft that need stabilising, Flywheel is one and the Pulley end is the other.. the two act in unison. Changing this designed relationship without an engine rebalance (in the Least) will affect the vibration frequencies ;-)

Link to comment
Share on other sites

Well.. LW pulleys effects are bit more insiduous than "odd" vibrations.

Crank starts to "whip" and soon wipes the bearings .. this is not new info though.

Don't believe it ?. No worries..but I've seen it all too often.. however if you prefer, this may just be the opportunity to gain some experience firsthand *wink*



Link to comment
Share on other sites



A few real world examples would be nice. All this talk of whip and wiped out bearings seems scaremongering to me. How many engines have you seen with ali pulleys that have wiped out their bearings? 1? 2? 20? What engines in particular?


How do you explain that some engines have no harmonic dampers? I have never seen a race engine with a lump of cast iron on the front unless it has been something low tech.


How do you explain that in the USA (where people sue you if you look at them the wrong way) there are dozens of companies selling light weight pulleys? There are probably thousands of road cars in the USA running these. Our own Yankeedoodoo who runs a 2 litre Zetec has a Esslinger (respected US tuning company) ali pulley. He also runs an ali flywheel (another no-no according to some balatchatters, even though they have no personal experience of them and I have sold dozens since the mid '80's).


Why is it OK to remove seven kilos from the flywheel and not one kilo from the nose of the crank? Surely removing weight from the back of the, engine mating it to a different transmission and wheels would upset things just a tad.


How do you explain that all the successful engine designers (not builders) told me that it was an acceptable thing to do (although to be fair not 100% without risk)?


How do you explain that some very respected crank balancers expressed the same opinion as above?


From recent threads it seems that there are engines that sh*t themselves even without the benefit of a lighter front pulley.


How do you pinpoint a particular engine failure to one particular component?


This has all been covered before when Julian Thompson asked me to have some K-Series ali pulleys made. If you do a search under ali pulleys you will find about three pages of talk. My conclusion at the time, as it is now, is that nobody knows (including me) and anybody who does think they know is kidding themselves. Fitting an ali pulley is not without risk but neither is extracting twice the horsepower from a production engine. You do this at your own peril. Is it an acceptable risk? I wouldn't have one on my own engine if I didn't think so.


So less talk and a few example of failures please.


Bare, this is not a personal attack on you (or anybody else). Recently when I have put fingers to keyboard what I have said may have come across wrong (seems to happen a lot). If you have some examples of engine failures due to ali pulleys I would really like to know about them please. I may learn something. So far I have spoken to everyone and his dog at all the engine building firms I know (I know a lot of engine builders) and nobody has dissuaded me.



Link to comment
Share on other sites

Most 4 cylinder inline engines like the K and XFlow don't need a vibration damper. If your engine was fitted with a damper and you remove it, it's likely to end in tears hence the horror stories.

The reason short ingines like the inline 4s don't run dampers is because the crankshaft is comparatively stiff, and the dangerous vibrational resonances are above your maximum RPM. Reducing weight pushes the danger zone to a higher RPM, so you should be safe.


Rebalancing is most a question of personal choice, but changing to a lightweight flywheel definitely causes more of a balance change than a pulley change, and I think most people would go for a rebalance. The problem with clutch covers is that you have to locate the cover accurately if you want the balance to be retained when you remove/refit it.


Upgradeitis ward, awaiting open wallet surgery. 100,016 miles

Link to comment
Share on other sites



Sorry to hear about the engine situation - not having been to Brooklands last weekend I did not have the opporunity to push the PC monster *wink*


Sorry, could help myself saying that. Last year I came with a friend and he was quite concerned when it was being pushed, but I (unknowningly at the time) said that it always did that and you would have it fixed in a minute (which on this occasion you did).


On the pulley front, I agree that there would appear to be loads of poeple fitting these to all kinds of cars in the US Nissan 20DEs, Issuzi-Lotus 4XE etc ... without apparently ill affect.


Greg, Q 86 NTM (Green 185BHP XF)

Link to comment
Share on other sites

My car's thottle response is noticably sharper with AMMO's lightweight pulley; this is exactly what I wanted when I asked him if we could make some!


I've being giving it some thought since bare re-raised the issue and I just can't see any of the dangers. I know I am not qualified to comment technically but a common sense approach from me sees my engine spinning a bloody great car on one end of the crankshaft and a little pulley driving an alternator and a sump pump on the other.


I just can't see a problem and would more likely think that my crankshaft will snap when I fudge a downchange and treat my motor to a 12000 rpm festival.


PS AMMO have you got any of the pulleys left?

Link to comment
Share on other sites

Don't believe it Huh?? *wink*

Just because somebody makes and sells something there is no reason to expect that it is usefull or even not Harmfull.. that's just utterly naive.

Basic Example : VW aircooled Motors.. Lotsa Shiney Alumunun pulleys available from lMany Vendors, worst thing you can do to those motors is install one...

Berg sells an "Increased weight" pulley for performance puposes! Only the knowledgable buy them tho.

Most purcgasors are simply unaware of the reality.. lighter is Better.. every Fool Knows that :-)

Many British engines had stamped pulleys.. Not exactly an enviable precedent or History there tho... is there?

Bit closer to Home.. Honda engines DO wipe bearings with anything less than the OEM pulley,.. can't imagine a K series to be superior in any way shape or form to a Honda Unit.

Cranks need some counterbalance at the not driving/useless end to try and keep both ends roughly together.. to prevent whipping basically.

Obviously there are those that don't believe this.. So be it.

But back to my initial comment: what exactly are you expecting from reducing the Pulley weight??

Same effect as a lightened flywheel produces.. (in a smaller proportion) Faster Revving in First gear and no difference whatsoever from that point on?


Link to comment
Share on other sites



In the case of the VW aircooled engine the worst thing you can do is be in possession of one in the first place 😬 This is a a low tech 1930's design which may have a tendency to fall apart anyway. I wouldn't know as they are of no interest to me at all. Although a four cylinder engine, it is flat four boxer, so a whole other bunch of other considerations to take into account. If the engine is operated continously on the node of the torsional (droning on at 55 mph whilst going down to Cornwall to catch some waves), then I can see why it would fail.


The Honda is a contemporary engine. I will do some research and see what comes up. Thanks for pointing it out.


On a different note, I ran a race and championship winning engine for four seasons with nothing at all on the end of a stock crank. The nose just stuck through the timing case with an oil seal seal. It was also revved to far beyond what it was ever intended. Just another snippet of information which may be of interest. Maybe not a good example as it was a V-Twin motorcycle engine.




Yes, I still have some pulleys. Four to be exact. Annoyingly a couple of people who put their names down originally seemed to have disappeared off the face of the planet. I have emailed them direct but have had no reply. Puts me out of pocket. Just a bit perplexed why anybody should say yes to something and then not even have the decency to reply (maybe they are women posting under a pseudonym). Not particularly bothered. They will go eventually. I'll chalk it up to experience. Next time we organise something like this I'll make sure to get the money up front.



Link to comment
Share on other sites

IMO the harmonic damper is only aimed at engines that spend most of their life running at constant revs and loading " Motorway use" This type of use has little or nothing in common with how a Seven is used. Also when an engine is tuned and fitted with a lightweight steel crank and rods and flywheel the natural resonace that this harmonic damper was designed for will have changed and therefore it will be of little or no use. But the main reasons for me dumping mine was that my K was built with use at higher revs in mind this necessitated fitting a smaller crank pulley in order to reduce the alternator revs.
Link to comment
Share on other sites



What you say is exactly what I have been told by the engine designers and crank balancing people I have spoken to. Simplistically, harmonic dampers only work at one rpm. If you avoid running continously at the node of the harmonic (usually around 4,000 rpm, but varies from engine to engine) then you will have no problems.


Not managed to find any information on Honda engine failures. I really don't know anything about these and don't know anybody who works on them either. I could go through my Touring Car contacts but I don't suppose a full blown race engine resembles a modified road engine much in the crank department.


Does the Honda engine have a balance shaft arrangement? I seem to remember something about this.





Edited by - ammo on 20 May 2003 07:34:57

Link to comment
Share on other sites



I'd like one of those pulleys but will unfortunately have to wait until finances allow. Write my name on a post-it clearly visible before you let the last one go!


Btw, I have a wet-sump, does this matter? If I sometime in the future go for a dry-sump from either Caterham or Pace, will I have to toss it?


PS is it red?

Link to comment
Share on other sites



I have scratched your name on one with an old nail (only joking).


Not red I'm afraid. The coloured anodised parts are cosmetic anodised. These are hard (very hard) anodised and come out a greyish colour.


Most people are using them with a wet sump. You just have a redundant bit at the front. They also work with the Caterham dry sump. Not sure about the Pace as I haven't seen one yet.



Link to comment
Share on other sites


The development of the Harmonic Damper on straight six engines was the breakthrough that Henry Royce made when RR produced the first production six cylinder engine.


If the engine hits low order torsional resonance then the vibration amplitude will build up and snap the crank if the engine is run at that frequency and this certainly happens with straight sixes. Higher orders are less damaging as amplitudes are lower but they can produce poor NHV characteristics.


Balancing the engine has no effect on this behaviour as balancing only affects lateral vibrations.


Whether or not you need to re-balance an engine depends on how it was originally balanced. If the crank and pulleys were component balanced then you should be able to change individual components as long as they have been balanced before fitting.


If the bottom end has been assembly balanced then changing an individual component means you have to re-balance.


I made some comments on the earlier thread about replacing the crank pulley.


There are two seperate points that need to be considered.


Changing the mass of the flywheel and/or pulley will certainly change the resonant frequency of the crank assembly. It is possible that lightening may move torsional resonances into the running range and if this is the case serious damage can occur.


Calculating the torsional and lateral behaviour is possible but quite time consuming/costly and it seems to me that there are sufficient Ks running with lightened flywheels that there shouldn't be too much concern.


Removing a damper from and engine is a different issue. If there is a torsional vibration in the running range of the engine then removing a damper is dangerous.


The Jag XK engine has a very heavy cast iron damper which is really ugly. Terry's in the States make a very elegant anodised aluminium replacement which still has a visco-elastic element and still damps torsional vibrations.


If the damper on the K only removes a slight roughness, which seems because as others have already said it is very rare for 4 cylinder engines to have serious torsional problems, removing shouldn't be too much of a problem.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Create New...