MAJOR Problem

Fitted my new gaskets and spark plug a couple of weeks ago without problem. Bike started no problem but didn't go for a test ride.

Decided to take it out for a ride on Friday night and something is seriously wrong. After about 5mph the bike makes a horrible rattling sound from the engine/gearbox area (could even be the head). It won't change gear very easily and I don't think it will go into 3rd at all!

Doe anyone know what the problem could be? I thought I had got my carb problem sorted so surely it can't be that? Does anyone have any ideas?

The rattle is a horrible sound and is very loud!

The rattling can't be caused by the carb.

Since you have fit new gaskets (cilinder gaskets I suppose?), my best bet is the distribution chain.
Check first if the timing is right, check the tension.
+ check the valve settings, ignition timing, clutch setting or friction disk wear... the regular issues.

Other than that... gear box problems. (wear)

Hi James
Sorry to hear of your problem, have just had a call from the garage telling me my motor cannot be upgraded to cdi it is to early so I am in a right cleft stick, I can buy a new motor which will require a manual clutch lever etc or muddle on with my electrics new coils etc.
Oh life can be a pain
Regards Tufty

Sure it can be converted.

You've got 2 types of cranks in the ST70 engines:
L (long) type: flywheel brand Mitsibushi, Daijatsu,...
S (short) type: flywheel brand Hitachi, flat flywheel

L-type: fit a Jingcheng CDI ignition, plug and play on the crank! Or a 6v inner rotor (Kitaco,...) with 12v outlet.

S-type: swap the crank (Honda NT for example) or use a short piece that slides over the crank tap.
Which converts the crank tap an 12V tap. (available in Holland, custom-made )
So you can fit ANY 12v ignition system (regular, outer, inner rotor,...) except the Jingcheng ignitions.

By the way: there are new 12v CDI engines with semi clutch available.
+ a clutch conversion is quite cheap and easy. (check out my sales topic)

Made a decision last night to leave the bike for a couple of months as I simply don't think I have the time or expertise to try and fix a problem of this magnitude.

If the gearbox is damaged then it means taking the engine apart which I don't fancy doing... I could pay someone else to do it but god knows how much that will cost!

I think I managed about 60-70 miles this year on the bike before my problems

There is always next year!

Good luck with your conversion Tufty!

James, don't throw the towel now!
Your just one or a few steps away from succes.
Once the engine runs smoothly, it will last you forever.

Make sure you did all the basics right.
Right amount of oil and all that.

Spare parts (engines) are cheap.
complete ss50 engine (4 gears, manual clutch) 200€
complete st70 engine (3 gears, semi) 150€
st70 engine without cylinder head: 30-100€


Tufty, one other thing: 6v CDI ignitions also exists, but may be hard to find.

Hi James

If the bike cannot be ridden and you are unwilling at this moment in time to pay someone else to look at it then you have nothing to loose by looking at it yourself. Diagnosing a noise at a distance is almost impossible and it could range from a loose camchain which has jumped a couple of teeth to a loose clutch or a cracked gear.
As long as you do it by the book (or the manual in this case) and keep either a written or photographic note of everything as you take it apart and compare this with the photos in the manual you will I am sure come across the fault. If it isn't immediately evedent when you are taking it apart then close examination of all parts should reveal any damage and if you don't find any then it may just be that it needs reassembling correctly which may cost no more than the price of a gasket set and some new oil.
The beauty of these engines is that they are about as basic as a 4-stoke engine can be and are ideal for the mechanical novice to learn on. You can have it out of the frame in 15-minutes and the crankcases separated in about an hour, if by then you have lost heart you can stick the bits in a box until another time when you feel up to it!

Thanks guys. I am not going to give up on it, I really want to get my running issues sorted and will do anything to get it working. I have come a long way, when I started I didn't know anything about these bikes and now I have learnt so much. I can even remember having to ask Waynus on how to remove the headlight switch

I am going to try and get a video to show my problem first and then might strip it down after I have ordered a new gasket set.
I have a workshop manual for the bike and my uncle is pretty experienced with engines so could help if I get stuck. I personally think that something is broken in the gear box or the big end bearing has gone (read about the same issue on the planet mini trails website). It's strange how the bike worked one day and then another it didn't.

Thanks again, I will keep you all updated!

Sorry to hear the news James.
I think I have the same problem with my chaly. After about 1000 miles of running perfectly, my chaly has now started making a clanking sound from the engine. It makes this noise all the time when the engine is running, when the engine is stopped and being turned over, with the spark plug removed, still makes the noise.

It is very hard to pinpoint the exact location of the noise.

Would worn gearbox/clutch cause this? or is it more likely to be a timing problem?

The gears still work and the bike rides ok, but i am not going to ride it again until I get this noise fixed.

anyone got any tips on trouble shooting?

many thanks
Joe

The first thing to do could be the screwdriver trick.
Put the tip of the screwdriver on different places when the engine is running.
This helps to locate the spot the noise is coming from.

Rattling can have a lot of causes, here are the most common ones:
- bad valve settings
- bad valve timing or worn distrubution chain/wheels
- bad clutch setting or worn plates
- gearbox troubles
- ...