GN250 gearbox-engine

**BlackMDK** · 20th May 2007, 18:38

I’m in process restoring GN250 that has been sitting for 5-6 years and before that guy said it stopped with grinding noise and loss of power and he could not get in to the gear, engine was still running ok according to him. I took bike apart and engine is on the bench. Took of magneto and clutch cover and found decent amount fine metal shavings where clutch is. Clutch seams fine so shavings came from somewhere else. Does anybody have any idea what it could be?

I’m realizing I need to disassemble whole engine and gearbox to find problem but I’m not to keen on $200 for set of gaskets, can I successfully reuse old ones?

How hard is to get piston back in as I know on the car you need to have special tools to get piston back in to the cylinder?

And lastly does anybody have tools to reset valves?

**Buddy L** · 21st May 2007, 18:42

all i can help with is say
1... you will need new gaskets as im sure that they are nackered.

2... you don't need a special tool to put the piston back in, just a secound set of hands to make it easyer.

**twinkle** · 21st May 2007, 18:49

If you find you want the workshop manual pm me an email address to send it to

**Conquiztador** · 21st May 2007, 20:13

Yep, you will have to split the engine. If you want the crank off then you will also need a special tool to pull the magneto off the shaft. But you might decide to leave the L/H side intact and only take off the R/H side of the casing. Should allow you enuf insight in to what is worn.

Re pistons and rings. Put some oil on the rings and inside the bore before you push the piston back in to the cylinder. Easy to damage the top edge of the rings when squeezing them together by dropping the barrel on. Also set all ring gaps 1/3 turn apart. There should be 3 rings including the oil ring.

What else...yes, clean out the oil pump. No need to assemble motor just to find out that the oil is not getting where it should (normally you find out this by the backwheel suddenly stopping rigid at 100K/h...)

Oh yes, you can re-use old gaskets. As long as they are intact and not in pieces. Some gasket glue from Super Cheep fixes that (and at a cost that affords you to have a doz of cold ones to keep you going while in the garage)

My guess re what happened: low on oil... if the cam is black then its more then a guess.

Good luck

**BlackMDK** · 22nd May 2007, 17:49

I cannot yet say what is wrong with my engine as I only managed to get head of with great effort. But I can guess that reason for it being broken has to do with very poor DIY job that somebody did. Bolts where so tight that I needed 1m pipe for leverage to undo them (and I’m not talking about 4 big bolts that hold head). Gaskets are missing instead it looks like that they used 10sec glue???. Wall of the cylinder looks good no scratches same goes with piston at least some good news.

**BlackMDK** · 22nd May 2007, 22:02

Now iknow it is bearing on conroad / crankshaft, anybody has any idea how much is would that cost me?

and second one is insted of head gasket i have 5 steel shims is that what head gasket supose to be or there is somthing else going on

**Conquiztador** · 22nd May 2007, 23:14

Originally Posted by BlackMDK

Now iknow it is bearing on conroad / crankshaft, anybody has any idea how much is would that cost me?

and second one is insted of head gasket i have 5 steel shims is that what head gasket supose to be or there is somthing else going on

My friend, I hope the rest of the bike is in good condition... Sounds like the motor has seen its best days. Perhaps time to buy a good s/h one and fit. Should not set you back more then $300 - $500. And then use the best bits from the current one as spares. As the GN is a very common bike you will have no problem finding a motor.

It now makes sense re the tightness of the head and the glue. The "shims" would have been leaking. These use a single gasket for the head. I have seen two types: One has a metal ring up against the bore. The other is of a dark grey gasket material. I have used both types and they work well.

Good luck.

**Squiggles** · 23rd May 2007, 09:34

ive bought a whole set of gaskets off tardme for $35 in the past... same gasket set as an 82-85 dr250 i think it was.... easiest to get another motor for a gn than buy new bits, i bought one for mine for 150 a couple of weeks back

**BlackMDK** · 23rd May 2007, 10:45

Where did you get engine for $150

**Hanne** · 23rd May 2007, 11:35

trademe

i've got a munted engine here too but none of its bits are any good to you... conrod will be had it after the stress its been through and had a lot of metal in the bottom when i removed the sidecover to check the clutch etc

**Squiggles** · 23rd May 2007, 11:40

^^ gah, shes logged in on my computer!!!

**FilthyLuka** · 24th May 2007, 18:43

Originally Posted by Conquiztador

Oh yes, you can re-use old gaskets. As long as they are intact and not in pieces. Some gasket glue from Super Cheep fixes that (and at a cost that affords you to have a doz of cold ones to keep you going while in the garage)

Dont do this... people made gaskets for a reason. That reason is the gasket goo is patu and should only be used on the tappet cover of the GN, spend the cash (its feck all, i did a complete top end rebuild for $120, talk to colemans) and do it right.

Originally Posted by BlackMDK

Now iknow it is bearing on conroad / crankshaft, anybody has any idea how much is would that cost me?

and second one is insted of head gasket i have 5 steel shims is that what head gasket supose to be or there is somthing else going on

hehehe, yeah that happens when you dont use good oil and keep a GN on the motorway every day without service... 'parrently there was this one dude who had a ball from the bearing shoot thought the front of the crank and through ze started motor.

Pretty much what happens is the patu or lack of oil makes the ball bearing skid instead of roll, effectively wearing a flat side on the ball and causing problems.

Be that a warning to ginny owners! if you use the motorway every day, be nice to your engine!

As for the bearing, unless you can source a (good) second hand engine for the old girl then dont bother getting a new one. Just replace the bearing, put in castrol gtx20-50 and be on ya way. Ill also be happy to assist with the reassembly of the engine if you want

Talk to colemans, GN parts are cheap, definetly cheaper than an engine that has had god knows what done to it.

Oh! and while your waiting for bits to arrive, jet the carb...

Denis