"The Hot Ticket" performance mods

[greevous]

Wasn't sure whether to post this under engines or scramblers, but we'll give this a shot. This is just a late night thinking-about-bikes-when-you-can't-be-working-on-them post.

For those who race or those that just like futzing with the machines, are there any "Hot Ticket" modifications that are common on the Challengers? Things like exhaust shapes / lengths, increasing the height of the gasket under the cylinder head, carb tricks, clutch modifications...

It's always interesting to find out about work-arounds or improvements that have become traditional fixes to suit the peculiarities of a bike.

[Kim275]

Hi Grevous,
Many of us guys who race Greeves championships have made mods to bikes.
I have done some on my Griffons.and my dad's MDS .......some of which should apply to challengers

1. To go faster round a race track - first service/improve your suspension and your brakes! before you bother with your engine. Decent set of rear shocks and service your cerianis - or bananas)..
2. Ignition - change your points for elec ignition (I have fitted German PVL and it works well) - helps at higher revs - and also helps you start the thing in the first place !!
3. Carb - overhaul and tune (mikuni will help you run better but in UK would make you ineigible ot race pre65 or 68) - Amals if in good condition are not an issue.
4. Octane booster in fuel to compensate for the 2-stroke oil mix
5. Compression...gap your rings and make sure piston not worn. replace if you need to . You can if you want to raise your compression ratio by skimming your head or by thinner gaskets (note gasket is between barrel and crank...there being no gasket on your cylinder head)......if you run a higher octane fuel,,,but beware you run a risk of holing pistons etc......Simon at Nametab Eng recommends no more than 12:1........and he knows his stuff.
6. Not sure about exhausts on a challenger........but I put an ian Bain exhaust (big suck thorugh job) on my dads MDS and it now flies - but of course you may need to change exhaust port timing......
7. Air filter - run a moderm motocross two part foam filter - a friend struggled all last season with his Hawkstone....we adjusted carb settings - new plugs - we tried everything and the thing wouldn't go fast.........I persuaded him to throw away his paper air filter and replace with a twin air...and his bike flew

The moral of this one os that it is sometimes the basic simple things that can give you the best results!
Hope this helps
Cheers KIm

[Colin Sparrow]

Best race tuning advice I ever heard - get the engine into tip-top condition first. You cannot tune a worn-out engine!

[greevous]

Thanks for the suggestions. And all-for-fun question to begin with...

My uncle had a Sherpa-T that the previous owner had drilled every spare bit of metal out of. The cylinder cooling fins looked like swiss cheese (tended to run hot... weird right? ), the brake lever on the bar was drilled (as was the brake arm on the hub)... If there was spare metal it was gone.

I was also just reading an old magazine article entitled "Service-Shop Lore" listing a bunch of modifications for the BSA A50 and A65 engines. In addition to a couple suggestions about better ways to run the clutch cable or adjusting the air-cleaner deflectors (minor 5-minute adjustments) it also included a recommendation on helping out an engine that suffers from oil starvation: drill a 3/64", 30˚ hole "through the connecting rod web and into the middle of the big-end bearing." Adding "this is a major operation, but with care it can be done by the private owner, when carrying out a strip-down."

Take a bike that for the last 40 years has been ridden and worked on by mechanics, racers and weekend riders, and it's a pretty safe bet that if there's a chronic weakness, it's known about, and if there's a way to squeeze a little more power / acceleration out if it - it's already been tried.

[greevous]

Kim, somehow I completely missed your post when responding! Those are awesome suggestions!

•*Definitely plan on swapping out the front shocks on the leading link. Haven't decided on exactly what make yet.

• Currently running an AMAL but that will probably be updated as equipment restrictions aren't a concern.

• I had been wondering about the availability for electronic ignitions for the bike. Local guys at Rabers didn't know of a Greeves-specific version that would work, but they're mostly Tri/BSA/Nort guys. Definitely going to look into that.

• The bike has new pistons + rings, so that's set

•*I had also heard about "tuning" the gasket height... certainly a fun thing to play around with.

• Love the exhaust idea. Would love to find out more about performance differences (if any) between Silverstone / Challenger exhausts; see if there are any other things people have played with. Also, I couldn't find much info on Ian Bain exhausts - any links or is that more of a word of mouth connection.

When it comes to adjusting exhaust port timing, would that "adjustment" involve grinding down the piston skirts?

• As for the air filter... no reason upgrades have to be complicated.

Again, thanks for the ideas. The machinist and my main workshops are in San Jose, about 60 miles south of where I'm currently living and the welder is about 20 miles West of here - so getting anything done is a slow process. Leaving me with plenty of time to think about other things to do.

[Kim275]

Hi greevous - no worries......

re Shocks - if you are US Califirnian based - probably Racetech..expensive but good!
Re elec ignition for Greeves - I know of three options in UK...and can recommend 2 of these as they are fitted on my Bikes and work.

Simon Bateman of Nametab does an electronic ignition - I have it fitted to my MDS - contact +44 1527 522266 - mention my name.

On My Griffons - I have a PVL (which is a top of the range solution..i.e German ) - Talk to Terry Sewell of TDS services .....he could advise whether they would work on a challenger.....+44 1375675857 - mention my name.
Third option is Richard Deal - of Greeves.........I can't recommend - but only because I have no experience of them - maybe some other members have a view on these?

RE compression ratio - be very careful on this one especially adjusting gasket thickness . If you reduce the gasket thickness you will raise piston height - and indeed increase the comression.....but you also alter the position of the piston and reduce the squish clearance ........You need an expert engine tuner to work out the best option which might be to leave alone - or skim the head or adjust gaskets. Suggest you get an engine tuner to check the current compression ratio...11:1 is good and take his advice on whether to increase towards 12:1 - You would need to increase fuel octane and as per Colins advice - make sure your mechanics are sound - piston/rings/bores and bearings.


Note for QUB's they I believe started with 13:1.....but were reduced to 12:1?? Kenny or Druid might know the history??

Either way - I run mine on 12:1 which is LESS than the original spec. Re Exhausts - Ian Bain only does them for a Hawkstone/MDS.........realistically you need to find somebody in the US who can do you a bespoke exhaust

To achieve success you need an engine tuner and an exhaust maker......who can work together. I am no expert (I just ride them !!) but have seen the results on my MDS. In this case the exhaust maker (Ian Bain) knew what he reuqired in terms of exhaust port alterations and got Simon of Nametab Engineering to adjust to match the exhaust.
Just adding an exhaust may change the characteristics - but won't necessarily give you more power!....and you are wasting money. Equally changing your port without the exhaust will kill your performance. As these bikes are already tuned racing bikes!.....in fact Greeves with Brian Stonebridge achieved a lot of success because they experimented with Exhausts shapes and porting on HAwkstones....and with Dr Blair on the QUB's - so if you can improve the Challenger you are following on a great tradition!!

Be interesting to hear from any members who race challengers on any experience they have had in these areas. (as I ride griffons and an MDS)
Cheers Kim

[Colin Sparrow]

You can run a PVL on a Challenger. I used one on my Silverstone and it's the same engine. Very satisfactory piece of kit. Straightforward replacement for the Stefa, but you must set the ignition timing with a strobe.

[stormer254]

A good mod is to fit a mid to late 70s expansion chamber, to replace the original low volume device. You should find a good improvement without the cost or risk of designing and building a new one. Also when playing with base gaskets and compression ratio always check your squishband 25 to 30 thou!

[greevous]

stormer, any specific make, model or brand of pipe that you'd recommend looking at?

[stormer254]

I would go for a CZ, Maico or Husqvarna, they all went well and the engines are still fairly similar. choose the one that needs the least work to fit. Under slung I would say CZ or Bultaco, high level Maico, most but not all Huskies go over the engine so not so useful! You will have to adjust the first part because of the frame beam.

[Andy Z]

Circle F

Another candidate could be the from the Suzuki TM series; - Kevin at Circle F exhaust in Houston does the one pictured below for $200 plus shipping.

I can also recommend Kevin - his prices are very reasonable and he does a pipe which will fit a Challenger, but you have to make your own header pipe. That is unless you can get your bike to Kevin's workshop, in which case he will do the whole pipe.

Cheers,
Andrew