Camshaft wanted

[JHZ]

Hey Guys,

Was in the process of rebuilding my MadAss engine (I believe it's a Lifan 120) and managed to damage the Camshaft so I'm looking for a replacement. It's a 74mm shaft with 6.7 mm displacement and has the three holes on the sprocket face. If anyone has replaced theirs and wants to sell the old one, let me know.

JHZ

 

[Cactus Jack]

These cams are 74 mm long (overall length) and have 6.8 mm lift ... 21 mm base circle ... 27.8 mm overall height when measured including the lobe plus base circle = 6.8 mm lobe lift ...

NEW GPX 7MM RACE CAM, DUCAR LIFAN THUMPSTAR DHZ PITPRO - eBay Other Makes, Bike Parts, Motorcycle Parts, Accessories, Cars, Bikes, Boats. (end time 26-Mar-09 12:43:39 AEDST)

 

[JHZ]

Yeah I saw that listing. I'm thinking about it, but b/c it's a higher lift cam, I'd need to replace my valve springs and possibly do some piston mods which I'm trying to avoid. I might end up taking it though, let you know.

JHZ

 

[headsmess]

i got a set, arrived the next day, with the springs, make a noticeable difference.
also had the bad luck of getting a bad set,the first hes had yet. but he was more than happy to swap them for another set, which work fine. go dhz

if you can damage your camshaft removing it, i recommend you get standards, cause doing those springs can be....difficult. just so happens ive got my old ones here, only did a few hours with them....
sydney

 

[Cactus Jack]

WTF JHZ ?????? It's only got .1 of a mm more lift than your stock Madass cam ... that's 3.937" (thousandths of an inch) !!!!! Has your stock cam got the anti kick back mech on it ? I've got a cam that was sold to me by Bayseo on ebay as a Sachs Madass cam ... it's a 74 mm long 2 bolt cam with 6.7 mm lift , has CQ stamped on it and has NO anti kick back mech on it ..,

What was wrong with your springs Headsmess ? ... I bought one of those cams and springs to try out too ... curiosity killed the cat ... LOL ...

 

[headsmess]

my springs were fine, the cams werent though...ran like shit, put the originals back in, fine... hence, i got bad cams. returned em, got replacements, all sweet now.
the springs supplied with the cam are a LOT harder.i just swapped em cause i got em... and had made a nifty spring compressor out of a gclamp and a tube socket i just had to try out....and the way i rev it...best to do it.
now im still accelerating at 90km/h up hill, everything else standard.

hint...a magnetic tip screwdriver helps to get the retainers back in fiddly things.

now, before i go mad with a new set of rockers...does anyone make ROLLER ROCKERS?
else its build up with weld and into my mini mill.... and hours of frustration or some nice alloy, and days of frustration.

if not...anyone wanna buy some in a few months? one must test all new items thoroughly first, before placing on the market

 

[headsmess]

and im not measuring the suckers, but just looking you can see the difference in lift and duration with the gpx cams compared to the standards.

 

[Cactus Jack]

Roller rockers are a bit of a gimmick in pitbike engines ... A roller needs to be on the valve clearance adjustment side to prevent side loading on the valve stem , guide and seal ... I can see the roller pivot pin wearing out quick with the roller running on the cam ... The reason why they run a roller is so they can snap the valve open quicker with a steeper ramp and hold it open longer on the nose at full lift ... even with a short duration cam ... With rollers you need to use a hardened steel cam ...

As for the stock rockers ... the wear pad needs to be hard chromed like XR75 rockers are ... Stock XR springs are a lot stiffer than pit bike race springs yet the rockers last for donkeys years ... You can get your rocker pads hard face welded but then they need to be precision ground to get the arc back then polished ... Megacycle cams in the US does that and so does Ivan Tighe cams in QLD OZ ... Maybe Honda Nice , CRF or some other genuine Honda rockers are hard chromed and will fit ... ?

I've seen where a bearing with one side sealed is used on the small bearing end of some horizontal engine race cams ... That would prevent oil volume from being lost and all of the flow would be directed to the lobes where it's most needed to lubricate and cool the rockers ...

Horizontal engine cams weren't really designed for heavy duty racing use like XR valve trains were ... for a start , ball bearings have lousy load carrying capacity ... the balls concentrate the load to a small surface area so the PSI is heaps higher even with weak springs ... XR cams don't run any bearings at all and the lobes are near twice the width to aid in reduced wear and increased heat dissipation ...

I've compared the GPX cam to a stocker and there's a fair difference in nose duration ... The cam you sent back most likely had the sprocket flange pressed on out of index ... Whenever you fit a cam you should check the indexing /degreeing ... It would help to know the timing specs and lobe centrelines to assist but in most cases you have to work that out for yourself ... Most reputable cam grinders supply the needed info ... but not the Chinese ...

 

[headsmess]

yeah, i just googled roller rockers and see they are around, but they use skinny lil bearings, dont they? just one bearing? my gawd....
i got a set of old ct90 rockers somewhere, not a sign of wear, and it had to have been an old postal one, plus the next owner/s... polished, but not worn. pre cdi, so it would have to be before 84...no idea of the hours its been used for... a lot.

me thinks ima just gonna get a set of standards, and do the weld and machine option, try and source some needle bearings ...or two/three bearings so im using the whole cam face... got a pair of tiny double row bearings here somewhere...need four though, dont i? two per rocker... and they mightnt have the load capacity even then....

just found theseSKF - Product data think these are the smallest....

or i could try brazing some carbide to the faces...and get that ground to arc.... make a mess if it lets go though (my brazing NEVER lets go...lol)

and yeah, that was the conclusion we came to...the sprocket hub hadnt been indexed properly...

 

[Cactus Jack]

The weld has to be able to hack being hammered ... needle bearings etc are only good for racing engines which are pulled down and inspected regularly plus used for short periods on race days ... Ducati got rid of their half cage roller bearings on their cranks and went to full slipper with zero power loss on the dyno ... but the engine reliability was GREATLY increased ... For reliability and the greatest load carrying capacity ... nothing beats slipper bearings ...

 

[headsmess]

same deal with harleys in the draggies... throw the rollers in the bin and go bushes... but still, i like the challenge of making me own rockers...and the smaller radius of the bearing...what was that you said about curiosity and cats? hope my bike has nine lives...