'81 DT175 oil pump issues...again

[Nick60]

Good evening all,

I've read JW896's post of 02/09/2010 but still have some questions.

I've just put the top end back together after a rebore ( got a new barrel dowel, from Yambits, as I was told to, thanks Oldgit ).

Q1) On checking the oil pump "minimum stroke" the gap was at 0.55mm and had 8 shims. Haynes say it should be 0.20 to 0.25mm. I removed 4 shims and the setting is now 0.20mm.

What I can't get my head round is this... when the gap was bigger, was I pumping more oil or less oil?

Q2) Oil pump cable adjustment... When the cable slack has just been removed the pully guide pin does not line up with the "pip" on the pully.

The raised boss stops against the guide pin, and the "pip" is almost a 1/4 throttle turn from the pin.

From the boss to the pip the cam is flat and just after the pip the cam starts rising. On the current setting, on full throttle, the pully just reaches the highest point on the cam.

There is a tiny hole in the pully, which is only a couple of mm from the pin with the throttle closed, but I don't think this hole is the mark I should be using? My cables have no adjusters below the junction box so I'm stumped ( I have the "self adjusting" cable juntion box ).

Any ideas on what I should do?

Thanks in advance,

Nick.

P.S. Bike back together and snow forecast for tomorrow... bugger.

[Airhead]

Good evening all,

I've read JW896's post of 02/09/2010 but still have some questions.

I've just put the top end back together after a rebore ( got a new barrel dowel, from Yambits, as I was told to, thanks Oldgit ).

Q1) On checking the oil pump "minimum stroke" the gap was at 0.55mm and had 8 shims. Haynes say it should be 0.20 to 0.25mm. I removed 4 shims and the setting is now 0.20mm.

What I can't get my head round is this... when the gap was bigger, was I pumping more oil or less oil?

NOTE

Thicker shims increase pump stroke and output, Thinner shims decrease pump stroke and output.

So

You were pumping more oil with the biggest stroke 0.55mm, make sure the pin and match mark are aligned when measuring, you should get the marks alignment right before doing the stroke adjustment or at least be sure you are not on the rising slope of the pulley.

Q2) Oil pump cable adjustment... When the cable slack has just been removed the pully guide pin does not line up with the "pip" on the pully.

The raised boss stops against the guide pin, and the "pip" is almost a 1/4 throttle turn from the pin.

From the boss to the pip the cam is flat and just after the pip the cam starts rising. On the current setting, on full throttle, the pully just reaches the highest point on the cam.

There is a tiny hole in the pully, which is only a couple of mm from the pin with the throttle closed, but I don't think this hole is the mark I should be using? My cables have no adjusters below the junction box so I'm stumped ( I have the "self adjusting" cable juntion box ).

Any ideas on what I should do?

Thanks in advance,

Nick.

P.S. Bike back together and snow forecast for tomorrow... bugger.

You really must get the match mark on the pulley and the guide pin aligned when the throttle is closed. You have cable adjustment where it goes into the pump casing to facilitate this.

It is important to bleed the pump by removing the screw at the top of the pump until all air is expelled, then replace the plug screw.

Then what I do is start the engine and while it is idling I hold open fully the pump pully to allow maximum stroke for around 45 secs, this will purge air from the pump to carb oil line.

The little hole in the pulley is for a spring clip and is a safety feature to prohibit the cable from jumping out of the pulley cable recess

[Nick60]

Thank you yet again Oldgit, you're a champ.

I'm clear on what to do now. There is no adjuster on the cable so I'll have to replace or modify it but the snow came as promised so I have plenty of time to sort this out.

[YPVS TONE]

I seem to remember on my 1979 DT125MX that there was no adjustment for the oil pump cable as there was a self adjuster in the junction box under the tank which automatically took up any freeplay.I seem remember this had a cover on which you can take off to check and see if it is working OK .Tony

[Nick60]

I seem to remember on my 1979 DT125MX that there was no adjustment for the oil pump cable as there was a self adjuster in the junction box under the tank which automatically took up any freeplay.I seem remember this had a cover on which you can take off to check and see if it is working OK .Tony

Thanks Tony,

Yes, mine is the same, no adjuster on the cable itself. The self adjuster is fine but I think I have the wrong cable fitted as there's 20mm too much inner cable compared to the outer. Will try to get a universal type adjuster or send off for the correct cables, which means waiting a week or so.

Nick.