TZR125 Rebuild

[binge]

Okay, I dont know the history of this engine. I was given it by Gaz (Mate of mine). Who bought a complete running TZR from a brainless 17 year old.

Now the lad Gaz bought it from said it had just been rebuilt, And was still in its running in period. I have no idea on this fellas workmanship, The engine isnt producing nearly as much power as it should be, And I just want to know that its right inside.

I have been advised to replace the Piston, Rings, Little end bearing, and gaskets (obviously).

I've rebuilt 2 stroke scooters before, But only to fit bore kits. Now on this 125 rebuild, Is there anything else I need to consider while doing it?

Cylinder head Skim? Barrel skim? Bore to be honed? anything like that?

Also would it be a good idea to get the ports polished while its apart?






Ben
____________________
- Honda XL125S - CBR400 NC29 - VFR400 NC30 - CBR400 NC29 - TL1000R - TeeZeR Pit! - Bandit 12 - YZF450 - LuckyMX125 Pit! - Demon X XLR 140 Pit!
- Stomp KZ 160 Pit! - Demon X D-link 140 Pit! - CRF50F Mini-Pit - MonsterMoto 155cc MiniSM - Honda Chaly 150cc - Yamaha 98' R1
- Honda Chaly 140cc - Thumpstar 190cc 4v MiniSM - Aprilia RS125 Pit-Bike -

[bmwsport]

well you definately need to check the barrel for ovality and size, id expect some wear unless its a new barrel, find the bore size for a new barrel on that engine and go from there, cylinder head can be polished iwth autosol if its in good nick

[binge]

So are you suggesting I replace the entire barrel?

Can it not be bored slightly, And can I not fit an oversize'd piston?




Ben
____________________
- Honda XL125S - CBR400 NC29 - VFR400 NC30 - CBR400 NC29 - TL1000R - TeeZeR Pit! - Bandit 12 - YZF450 - LuckyMX125 Pit! - Demon X XLR 140 Pit!
- Stomp KZ 160 Pit! - Demon X D-link 140 Pit! - CRF50F Mini-Pit - MonsterMoto 155cc MiniSM - Honda Chaly 150cc - Yamaha 98' R1
- Honda Chaly 140cc - Thumpstar 190cc 4v MiniSM - Aprilia RS125 Pit-Bike -

[salty21]

if its like the nsr, rs barrels it will be nikosil plated which means a rebore would require re-plating which cost's around £100 so not really worth it unless new barrels are considerably more than that.
____________________
04 NSR 125(sold) ---- 03 CBR 600rr(sold) ----90 pan euro ST1100 '' ----02 CG 125
94 CB400 Super Four ---- 2000 VTR SP1 (sold) ---- 08 ninja p8f(sold, meh) ----05 CBR600rr

[stevo as b4]

TZR125L Barrels are all iron or steel linered. They can probably be re-bored up to 4-5times, and 2mm oversize. I would expect to see some wear, but get a proper set of kit for measuring the bore size etc, or take it to a decent shop with the gear to check it for you. You may only need to hone the cylinder and fit a new piston and rings. Do not ever fit new rings to an old piston or vice versa, as i have seen that cause failures when piston and rings are not changed together. The TZR should make 26bhp? so that would be 20-22bhp at the wheel in good condition.

If the motor is apart for new piston, rings, and a hone or rebore, then measuring the squish clearance and investigating the possibility of having the head skimmed or re-profiled to increase the compression ratio slightly should help the performance a bit IMO. I wouldn't bother doing anything to the porting of the cylinder other than making sure everything is clean and smooth. If you want porting work done on an engine, then send it to the proffessional tuner who has the equipment and expertise to actually improve performance instead of make it worse at best for most DIY efforts.

[Blue_SV650S]

What makes you think it is not producing the power?

Before buying stuff, you need to measure the old stuff ...

A worn 2-stroke normally shows signs of 'blow past' on the piston. i.e. just below the ring/rings you see carbon build up where some combustion gasses have passed the rings. These build up over time. A fresh engine won't have this, a long in the tooth one will.

Also measure piston ring end gaps - and look at the 'hone' marks on the bore. If you can't see any, its tired, if they are obvious, then its fresh.

The TZR has a powervalve, I seem to remember you talking about fitting a servo. So I assume you have the motor with the valve close? In that state it'll produce ~12hp right? IIRC on the TZR you can manually set the valve to fully open. This will leave you with a hole in the mid, but allow the full 24odd horse when she comes 'on pipe'

Oh and if you have put this motor in another bike, have you kept the original TZR pipe/expansion chamber? If you haven't - no wonder it is gutless!!
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The purpose of life is to fight maturity.

[binge]

The Powervalve is currently pinned fully open. Its running alot better now. Although I still think its probably got some more.

I think the problem may have been a leaky inlet manifold. I've re-built the inlet with a longer steel link pipe so it pushes into the rubbers a bit further. And its running ALOT faster now.

I was pushing an MGZR 1.8 along earlier. He started to pull away once we hit around 55mph.


So yea, Its running pretty quick now. Although 6th gear is still a bit gutless. I may go up 2 or 3 teeth on the rear sprocket.




Ben
____________________
- Honda XL125S - CBR400 NC29 - VFR400 NC30 - CBR400 NC29 - TL1000R - TeeZeR Pit! - Bandit 12 - YZF450 - LuckyMX125 Pit! - Demon X XLR 140 Pit!
- Stomp KZ 160 Pit! - Demon X D-link 140 Pit! - CRF50F Mini-Pit - MonsterMoto 155cc MiniSM - Honda Chaly 150cc - Yamaha 98' R1
- Honda Chaly 140cc - Thumpstar 190cc 4v MiniSM - Aprilia RS125 Pit-Bike -