First Topend rebuild. A few questions. Further help needed

[TomC]

I am planning on rebuilding my top end on my senda tomorrow, just have a couple of question so I know exactly what I am doing as I cannot afford to mess this up.

Firstly, I have purchased a piston kit, including new piston, rings etc. The rings are not fitted to the piston, there is a black one and a chrome one, neither have any clear markings on them and I am unsure which way round they should be fit or which should be on top/bottom. Also, is there any knack for actually getting them onto the piston, It looks like a tight fit and I dont want to force them on and snap one.

Is how I tighten the cylinder bolts important? how tight should they be?

When re-assembling the cylinder and piston should i put two stroke oil on the piston, rings and cylinder etc?

Thanks, Any help greatly appreciated.

[Frost]

Stip the bike of all panels including the fuel tank.
If you have a head gasket take the head off first
once the head is of, or you don't have a head gasket, take the barrel off.

Remove the piston clips from either side of the piston, using a screwdriver is normally the best way.
push the wrist pin out, the piston should then come off.

Inspect the barrel for any sign of damage (normally found around the exaust port). Inspect the piston and rings (this bits just for fun to see just how fucked it is )

If the barrel is okay, put the rings onto the piston.
The larger ring goes on the top and the smaller on the bottom. Look at the rings , just by the gap in the ring there should be a small T written on it. The ring goes on with this facing up.

The ring has to go on with the gap in the corrct place. Put one end of the ring into the gap in the piston, then push the ring down into the grove working your way around as you do so, lifting the rest of the ring out so its on the side of the piston rather than twist it too much.

Lube up the small end baering with 2 stroke before putting it back together.
Put the base gasket on.
Turn the rings round on the piston so that they are lined up properly, put a little 2 stroke on it and push the piston into the barrel. If you have to force it, the ring's arn't lined up properly!

Put the head gasket on and torque up the bolts.

If you don't have the torque settings, then just d them up as tight as you reasonably can. Don't risk rounding the bolt, but make sure their on firmly.

Make sure that you run the bike on 20:1 ratio premix for the first tank to make sure the oil injectors are operating.

Don't forget to rn the bike in atfter the rebuild!

[TomC]

Thankyou for the reply, very useful.
There are no markings on the rings so I will have to ring the shop I got them from today.

[Dom_]

Remember to drain the coolant!!! (if it is water cooled)

[TomC]

Taken the old piston out, the top is completely black, also the head has been actually sealed onto the cylinder by a previous owner, cant get it off, would need some force, am I better off just leaving it alone?

More worryingly than this though, I removed the tubes that connect to the head of the engine from the radiator and no coolant what so ever came out, does this suggest the water cooling isnt working?

[simon1221]

To take out the coolant you should have a draing plug somewhere, try using that before panicking.

The previous owner may have used some sort of instant gasket (in a tube) to put the head back on with.

If youve already got the piston out then leave it.

You can however just undo the bolts at the top (while putting everything back together, including spark plug) and turn the engine over a few times, the compression should force the head off.
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DNA50 (sorry) ->> TZR125l >> GPZ500S

[Scooby]

Get someone to help you the first time you do a rebuild, then watch how they do it, get them to take you through it step by step. Then the next time, you do it under their supervision. Only when you are competent should you be rebuilding them on your own.
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A big enough hammer fixes anything!

[TomC]

Hello, well I have got most of it back together now but when taking the nuts off that hold the cylinder to the engine, because they were rusted it actually took the bolts out instead with the nuts attached, which means I am left with a problem when assembling it again. Three of the four are not to bad and go in ok but the other has loosened itself so when I screw it in the nut just goes down the bolt and not any further into the engine holes. I cant grip the screw thread on the bolt to actually drive it in without the nut so I am struggling, any ideas?
I havent been able to explain this very well so you probably dont know what i am talking about

[mr jamez]

Wind the bolt in by hand, then spin one nut on so there is enough space at the top for another nut, then spin another nut on and pinch it up to the other by hand. Get an open end spanner on the bottom nut, then another spanner/socket on the top nut. Hold the bottom spanner, then tighten the top nut, you want the bottom nut to stay where it is, then the top nut will turn the bolt and wind it into the engine casing.

If they are rusted and seized I would replace them and get 4 new nuts to match.

[TomC]

Ah sounds like a plan, thanks

Are these bolts and nuts fairly universal? should I be able to get them from a bike shop without them having to be derbi specific?

[simon1221]

You could always soak them in oil/wd40 for a few days and see if that gets some of the rust off.
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DNA50 (sorry) ->> TZR125l >> GPZ500S