Author Topic: 1981 250H Crankcase Breather  (Read 185 times)

0 Members and 1 Guest are viewing this topic.

Offline Jacmac

  • Yama-Cheese
  • Posts: 4
1981 250H Crankcase Breather
« on: April 22, 2019, 07:06:28 PM »
Hello All,
Looking for some input regarding the 81 H model 250 and the crankcase breather that is integral to the clutch actuating arm/lever. Any help gratefully appreciated.
Basically the motor on the 250 is dumping a little oil out of the breather tube after it has been run for a while and then lent over on the stand. At the moment the breather hose is routed straight out with a rough 90 degree turn downwards once clear of the chain etc. When the bike is left nearly upright this does not happen. Looking through some photos in the genuine Yamaha manual, the pipe when the bike was new appears to be routed across the crankcases under the reed block/carb, but the picture showing this is not very clear.
Simple solution would be to run a longer pipe the same way so that when the bike is lent over on stand, oil cant make its way down the breather pipe, appreciate that is a little obvious. I just wondered about the experiences of others with H 250s and consensus on the correct way Yamaha would have routed the pipe. This is the first IT I've owned with a crankcase breather like this, all the others say on my 465J have had a vent nipple in centre of crankcases.
Many thanks

Offline JungleBiker

  • Yama-Rookie
  • **
  • Posts: 117
Re: 1981 250H Crankcase Breather
« Reply #1 on: April 22, 2019, 09:34:37 PM »
          The factory parts diagram seems to suggest that the hose has one 90 degree bend in it not far from the nipple:

--1982 Yamaha IT250J, was a wreck when I got it, now quite good!
--1967 Norton P11 (US project bike)
--1985 Armstrong MT500 (UK rider)
--1985 Honda XR600/628R (PNG daily rider)
-- lots of other junk spread across several US states and two big islands

Offline Jacmac

  • Yama-Cheese
  • Posts: 4
Re: 1981 250H Crankcase Breather
« Reply #2 on: April 22, 2019, 10:51:44 PM »
Hello
Thanks for that... Yes, had noticed that on Partzilla schematic, but I'm not sure that diagram shows the routing, just an illustration of the part. In my 81 250/465 Yamaha manual there is a photo where you can just make out that the pipe looks to go across the crankcases to the right hand side. My bike only dumps a bit of oil out the breather after being used and left on side stand, which is why I'm not 100% that it comes straight off the nipple and then 90 degrees downward, as it might act as a siphon if enough oil flicks up. This type of breather is not on the 82 J, but is on the 1980 and 81 YZ250. Unfortunately there aren't many Yamaha close up photos of the engine when new that I've found so far.
Cheers 

Offline fred99999au

  • Yama-God
  • ******
  • Posts: 4230
Re: 1981 250H Crankcase Breather
« Reply #3 on: April 23, 2019, 06:39:40 PM »
Total loss oiling system for the chain.

Sounds like your sidestand is too short or your gearbox is too full to me.

Offline Jacmac

  • Yama-Cheese
  • Posts: 4
Re: 1981 250H Crankcase Breather
« Reply #4 on: April 23, 2019, 09:15:53 PM »
Like the sound of an automatic chain lube set up!  :)
Yes, had thought about the side stand being either too short or the classic problem more often found on 465s due to starting while on side stand, bent frame mount. Gearbox was filled with 750cc as per manual. I never rely on the screw level check as often its incorrect. Cheers

Offline Jacmac

  • Yama-Cheese
  • Posts: 4
Re: 1981 250H Crankcase Breather
« Reply #5 on: April 23, 2019, 09:54:12 PM »
Just found this scan from 81 250/465 manual. See picture 3. Looks like pipe is supposed to run horizontally along sprocket cover.