Drive belt/Contra Spring

[EyeSee]

My Baotian BT50QT-9 has now done 1150km and, after 700km, eventually got my wife and I both up the hill home without one of us having to get off, (see my previous ‘More uphill speed required!’ back in February). To achieve this, I was just patient and allowed the scooter to run in. I did not change the roller weights or anything.

However, the last month or so, a problem appears to be developing and it is losing power up hill. If I make the 15km round trip journey to the island’s main town, the scooter manages the two steep climbs going there no problem. However, on the return, it struggles as it did when it was new.

I would point out that the problem started as daily temperatures here in Greece started to hit 30ºC and above, (possibly a coincidence). Is it possible that the heat is causing the drivebelt to stretch? Has anyone else experienced this? (There is a heat wave in the UK at the moment so I see on the news!) The scooter being black and the drivebelt casing being black too and poorly ventilated may not help either.

I will have the casing off at the weekend to see if there is anything obvious, eg worn belt teeth or oil. There is a possibility that some petrol may have seeped in recently. I had dirt in the carb and to get it started, I had to use throttle and flooded it several times. Petrol poured out of the carb and back to the air filter and leaked out all over the drivebelt casing! However, the uphill problem started weeks before the dirty carb problem.

Can anyone give me any advice on what my problem may be and any suggestions re: drive belts. I have already read some info on drive belts in Madtim’s ‘Roller answers needed’ and Joe’s ‘Drive belts’. I am sure it is gearing related, so please, no suggestions re valve clearances or spark plugs (NGK already fitted).

If I could resolve the above problem and still want to make a modification to improve my uphill speed, I get the impression a stronger contra spring would be a better solution for our particular situation and would help tension the drive belt if it is slackening in the heat, as opposed to fitting lighter roller weights, see quotes below:

From Cantlogin:
“The spring in the rear driven pulley only controls the gearing by varying the position the belt sits, in the pulley. A stronger spring would make the belt sit higher, giving a lower ratio (slower speed/higher engine revs), whereas a weaker spring will give a higher ratio (faster speed/lower engine revs). The real issue, which would warrant changing the gearing ratio, is whether the bike has low enough gearing to climb the steepest hill you need, and is not revving it's nuts off downhill at the other extreme, taking the power it has available into consideration.”

From www.teamcalamari.com/zuma/variator.html
“If your roller weights are giving you good acceleration, and a good top end, but when you approach a small hill the scooter slows drastically, this may be caused by having too light of a contra spring.”

Has anyone tried this? If they have did it work? What is the rating on the standard spring and what rating did you fit? Remember, I don’t want sports performance, just to get up hills with some respect!!!!! Visit www.kalymnos-isl.gr to see where I live and you will get an idea of the terrain!!!!

Many thanks

Eye See

[Spaceprobe]

What a nice part of the world, perhaps we should just all come and visit and give you a push. I know what you mean once mine got to 700 - 1000 k mark its performance improved all round. So much so that I am not going to change the rollers now. I wonder if a Kevlar belt would help since they are tighter and do not stretch so much but I am sure there are others on here who will know better. I take it you have adjusted the valves that always seems to be an issue with performance. Enjoy your heat wave. Rob

[Spaceprobe]

Just another thought in the new workshop book it does say that in hot dusty conditions the air filter should be cleaned more often. They say to rince it in petrol, squeeze it out then soak in engine oil squeeze out and re fit.

[EyeSee]

Thanks Rob,

A push would be welcome from any would be visitors to Kalymnos!

The air filter has already had a few rinses in petrol from the dirty carb/flooding problem and when I rung it out it seemed clean enough.

I am not sure about valve clearances as the scooter runs fine for a while. Again today, the scooter had enough pull to get up the first hill but by the time it got to the second, it struggled. Despite this, on the flat it can still reach top speed, although it takes more time. I get the feeling it is stuck in too higher gearing. When you are climbing a hill, you do hear it drop down a little, but by then it is too late and struggling.

Has anyone experienced a problem where the spring deteriorates and becomes weak or sticks? Or perhaps there is not enough lubricant to allow the two parts of the rear variator pulley to slide and they stick together?

Anyone replying please remember that up to 1000km, the scooter coped OK with the hills and that this is a problem that has developed since 1000km.

Thanks in anticipation everybody.

Regards,

Eye See

[hypojam]

Lighter Rollers Will Help or More likely fix your poor hill climbing problems.

Also check/adjust your valve clearances

[EyeSee]

Thanks Hypojam,

The point i tried to make in my last post was that the scooter was doing exactly what I wanted it to without putting lighter rollers in. Now it is not and I am trying to get help to find out why/ what has gone wrong.

Thanks all the same. If I have to do anything to the transmission, I will probably put lighter rollers in anyway while the front variator nut is undone!

Cheers,

Eye see

[EyeSee]

Hi All,

I have now adjusted my valve clearances, see ‘Valve Setting’ in ‘Hints, Tips & DIY’, but this has not solved the problem. I had already fitted an NGK plug.

I have also had the drive belt casing off and, apart from a lot of black dust, there were no signs of belt wear, oil or petrol, (see earlier comments). The only thing I noted was that I was able to compress the spring by hand and it did not return, the belt dropping down and jamming it in the compressed position. However, this is probably only possible as it is not running. I did start and rev the engine with the cover off, and observed everything doing what it should do.

As I asked before:

‘Has anyone experienced a problem where the spring deteriorates and becomes weak or sticks? Or perhaps there is not enough lubricant to allow the two parts of the rear variator pulley to slide and they stick together?’…… ie the part/half of the variator that compresses the spring to slide freely?

What if the rollers were worn? Could they stick in the outer position and make it harder for the contra spring to work? Note: I am not aware of any excessive rattling suggesting worn rollers.

Remember, the scooter was doing what I wanted it to and now it isn’t, so something has failed or changed.

Any suggestions? Change the spring instead of the roller weights? Any info on spring ratings/strengths, ie standard and slightly stronger?

Thanks,

Eye See

[EyeSee]

I’ve a confession to make – I am officially a plonker!

Last Sunday I said I checked the drive belt for wear. Like an idiot, I just checked the teeth and failed to use my brain, ie it is the splayed sides that are in contact with the drive wheels and will wear. All that black dust should have told me something. Anyway, this morning I have changed the oil, (1400km – 400km late and oil was very black), and had the cover off again. I checked the width of the belt and depending on how/where I measured it, it was 16.5mm wide or narrower with the steel reinforcement braiding showing, far less than the standard 18mm and 17mm minimum. Hence, I am a plonker!

OK, so I think I have found my problem and will buy a new drivebelt. However, I need to improve the scooter’s uphill pulling power to stop the same happening in another 100km or so and am still of the opinion that a stronger spring will be a better solution than lighter weights.

My reasoning is by way of a comparison to a tug-of-war match. Imagine four 20 stone men at each end of the rope. Take one off the end representing the front variator (equivalent to lightening the rollers) and the rear variator will win. Doing this, the tension in the rope (equivalent to the drivebelt) will be reduced. Adding another 20 stone man to the end representing the rear variator (equivalent to a stronger spring) would have the same effect. However, the tension in the rope will be increased. So, when I hit one of our long, steep mountain climbs here on Kalymnos, the rear variator will respond faster and put more tension in the drivebelt, reducing slip.

Does anyone agree?

I have asked earlier in this topic and a previous topic about contra spring ratings. Is there a specific size, ie length and diameter or a specific rating, ie wire gauge/diameter or something like kg/m for strength? If so, what is the standard and what would be the first step up strength wise. When I go into my local Greek scooter parts place, the language barrier is hard enough, so it would help if I knew what to ask for! I do note that on Beedspeed they talk about +15% and so on, but +15% of what? Scooter Assassins refer to RPM, but for the contra spring, I cannot see what RPM has to do with it.

Thanks again everybody.

Regards,

Eye See