Crank seal? dt125

[wizzer]

Hi guys, haven't posted in a while. I have a dt125lc which i use offroad where I live, My problem started recently when i tried to start the bike up after lying in the shed for about a month. It was difficult to start then as it warmed up it started to rev higher and the only way i found to bring it back down was pulling the chocke out; Therefore I suspect it's running lean?

From what i'v read it sounds like an air leak somewhere but how do i check for an air leak?

My suspicion is that itcould be the crank seal.

How do I check for a worn crankshaft seals?

Thanks once again

[Airhead]

if its a seal it will be the one on the left behind the flywheel rotor.

1: is there any petrol / oil in the magneto area?

2: Try spraying WD40 through the gaps in the rotor when she's running...aim at the seal....does it affect speed or tone from the engine?

[wizzer]

1: I checked under the magneto cover and it's quite clean, doesn't appear to be any petrol/oil in that area.

The bike now will barely idle, it revs up high without the choke then bogs down if you don't apply a little throttle

2: Tried spraying WD40 around this area, nothing seemed to happpen imedateatly but after a minute it started to hiss and pop from the exhuast which it's never done before.

Is it possible to replace the crank seal without splitting the case?

[Airhead]

yes it usually is youll be able to see when you get the rotor off.

you'll need a proper rotor puller...dont be hitting it with a hammer lol.

the trick is to carefully screw in a couple of self tapping screws at opposite sides of the seal, then warm the area slightly if possible and pull on the screws alternately

all this is just a guess but its often the case

[XJ6-boy]

In truth mate I dought it will be the crank seal’s as these rarely give any trouble and the only one that can leak air is on the fly wheel side (generator side) the other is submersed in oil and if that had gone all the gear box oil would drain into the crank case, more likely to be either the cylinder head gasket or my favourite the barrel base gasket, over time with the barrel and head getting hot then cooling down the head bolts work loose (these should be torque checked every 6mths or so) as they work loose it creates a situation over time were as a gap appears between cylinder head and barrel or barrel and crank case, the bike was probable running ok when you parked it up because the engine was warm (due to expansion of metals) but now it has cooled down the metal has shrunk creating a gap and damaging the seals. The best course would be to replace both gaskets (head and base gasket) also chk the carb is mounted securely also the reed block, but my bet is with the base gasket. The other option would be to compression test the engine but for the cost of two gaskets I would just replace them.

Have a goodie mate

[wizzer]

Ok think i'l probably just replace the seal because it seems to be the most likely problem at the moment.

I'l order a flywheel puler from ebay.

So I will need a Left hand seal for the flywheel side?

Thanks

[wizzer]

Ok thanks XJ6, I thought about that myself but thought i would be able to see any air leaking from around the base gasket i checked the nuts around the head aswell and they all seem fine also checked around the carb area with WD40 and couldn't find any problems.

[XJ6-boy]

I've working on 2 stroke bikes for many year so I’ve seen some problems over the years with air leaks on 2 stroke bikes and it is very rare the crank seals go wrong, in nearly all instances in my experience it's been the base gasket, if it was the head gasket you should see petrol oil in the water, if not then replace the base gasket first as this is the easiest job to do and a little tip when replacing the base gasket put some silicon sealant around the gasket before fitting, But not on the head gasket. I can’t remember on the dt but usually the crank seals are put in from the inside of the engine which will mean splitting the motor. (usually a small lip on the outside of the crank case stops them from coming out and the main bearing stops it going in)

[Airhead]

if the head gasket is the culprit you will see the engine temp hotter than usual but have you still got a temperature indicator on the bike? also the collant level will be reducing and if very bad you may have bubbling in the expansion tank

base gasket? well thats an easy one to check with the WD40 also

might as well try them wizzer eh

[wizzer]

Ok just went out there to test the bike and couldn't get it to start. It let off a loud bang from the exhuast when i was kicking it over even though the bike was cold.

I'm sure it isn't the head gasket because i replaced it in the summer when it blew and you could see where the leak was because of the bubbles however this time it seems ok.

I'l try start the bike tommorow and check with the WD40 around the base gasket

Thanks guys

[Airhead]

yeah and just double check the crank seal again, you implied evidence of a change before...see it it's repeatable, just so long as you can get her started

[wizzer]

Alright guys, think i'v found the problem, today i managed to start the bike so i tested it with the WD40 again couldn't identify any leaks in the gaskets, i was bored so i decided to start stripping it down, when i took the bost bottle thing off (YEIS) i noticed the rubber connector had a split and there was like a 5mm hole in it. Not 100% sure this is the problem but it's worth a try.

[Airhead]

yes that would do it, should be an easy and cheap fix, just get a new connector