Oil rising up through push rod guides!

Information relating to the Matchless G12 or AJS Model 31 650cc twin
Locked
tyajs
Posts: 4
Joined: Fri Mar 24, 2017 10:21 pm
Location: NEW ZEALAND

Oil rising up through push rod guides!

Post by tyajs »

I had a friend help me strip and rebuilt a 59 model31. It all seemed to go back together well apart from one annoying issue (a big issue that stops me riding). Before i stripped the bike and post rebuild, the bike pushed and is pushing oil up the push rod guides and flooding the rockers which ultimately finds it's way in to the inlet valves and bore. This causes the bike to produce blue smoke and foul the plugs till the bike runs like it has bad timing after 2-3 minutes. I have checked oil return. The pump seems fine and has been set up the right way round. Wet sump is minimal after sitting. Am I missing push rod seals or O-rings?
Mick D
Posts: 2886
Joined: Mon Mar 24, 2014 5:44 pm
Location: Aberdeenshire

Re: Oil rising up through push rod guides!

Post by Mick D »

Hi

Sounds like the crank case breather is not working correctly and crank case pressure is blowing oil up to / preventing the drain down from, the rockers - check the operation of the breather.

Regards Mick
User avatar
robcurrie
Member
Posts: 957
Joined: Fri Dec 09, 2011 5:33 pm
Location: Limpopo SOUTH AFRICA
Contact:

Re: Oil rising up through push rod guides!

Post by robcurrie »

There are no pushrod seals or guides; the holes in the barrels for where the pushrods are, are also return holes for the oil in the rockers and this oil lubricates the cams and followers when it drops down. There are smaller holes in the barrels to direct oil up to the rockers; on later models, there are brass metering plugs in these holes to restrict the oil flow. There is also an oil distributor driven by the exhaust camshaft which meters the amount of oil to these oil holes.

It could be the oil distributor or the metering plugs are missing that causes over oiling.

It could also be something amiss with the pistons and rings and oil is getting past them to the combustion chamber.

Rob C
tyajs
Posts: 4
Joined: Fri Mar 24, 2017 10:21 pm
Location: NEW ZEALAND

Re: Oil rising up through push rod guides!

Post by tyajs »

Thank mick, rob.. If I take the rocker cover off and start the bike I can see the oil rising up the push rods. The metering plugs are in place and oiling as they should. The rising oil level up the push rods are over oiling the rockers and ultimately the bore. The crank case doesnt have a breather other than the non return/breather nut on the end of the crank? The oil still rises when the rocker cover is removed. I would have thought the crank case would breath with the rocker cover removed? I have asked a couple of members in NZ but no clear idea of what the cause could be. Crank pressure sounds like the obvious cause but the removed rocker allowing the crank to breath would illuminate that?
Mick D
Posts: 2886
Joined: Mon Mar 24, 2014 5:44 pm
Location: Aberdeenshire

Re: Oil rising up through push rod guides!

Post by Mick D »

Hi

I think if the crank case breather is stuck removing the rocker covers will make things even worse - ie. the crank case can breath through the open cover via the push rod tube oil drain galleries.

On the other hand, could these galleries be blocked and you seeing a rising level from oil not being able to drain to the crank case?

Regards Mick
MalcW
Member
Posts: 626
Joined: Tue Oct 24, 2017 12:05 pm
Location: DEVON UK

Re: Oil rising up through push rod guides!

Post by MalcW »

Hi

I don't suppose it's possible that the oil pumps have been assembled incorrectly, with the feed gears larger than the scavenge gears, rather than the other way round?

Malc
User avatar
robcurrie
Member
Posts: 957
Joined: Fri Dec 09, 2011 5:33 pm
Location: Limpopo SOUTH AFRICA
Contact:

Re: Oil rising up through push rod guides!

Post by robcurrie »

Please check if oil is returning to tank. Is the crankcase empty and does the breather function correctly? Is the primary chaincase oil level just touching the chain, and does it keep this level after running the engine? Don't overfill the oil tank, half full is ok for most short trips. Does the breather in the oil tank vent properly? Are the oil pipes fitted correctly, feed at front, return rear?

Rob C
tyajs
Posts: 4
Joined: Fri Mar 24, 2017 10:21 pm
Location: NEW ZEALAND

Re: Oil rising up through push rod guides!

Post by tyajs »

No malcw, oil pump is configured correctly. Good points Mick. By crank case breather, do you mean the vent nut on the end of the crank holding on the rotor in place? The engine has no other external vents from the carnk case that I know of. Good advise too, Rob.. i did put one of these together many years ago when I knew very little, miraculously it went well for years with the odd tweek. Now I know a bit more, these bike seems so much more complicated! In uk for another week and heading back to NZ. I'll check through the points suggested and report back.
tyajs
Posts: 4
Joined: Fri Mar 24, 2017 10:21 pm
Location: NEW ZEALAND

Re: Oil rising up through push rod guides!

Post by tyajs »

UPDATE: problem resolved! The crank halves are from different years I suspect, at least not a matching cast. Behind the Cam wheel in the timing case is a 5/16 hole (or should be) that drains the oil at the bottom of the push rod tubes/cam lifters. I didn't have that hole drilled. The oil fed to the rockers was falling down the push rod holes and back filling slowly to the rockers again!! It had nowhere to escape! I think maybe the r/h case was from a later year that may not of needed a hole drilled. Its hard to know as there were so many mods and changes over those few years. Now I can carry on with all the other repairs, maintenance and tweaks that come with keeping these things on the road!
Locked