250 G2 1960 - OVER OILING

Information relating to the Matchless G2 or AJS Model 14 250cc Lightweight
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250 G2 1960 - OVER OILING

Postby Brian Hebditch » Mon Feb 19, 2001 10:41 pm

Following a full engine rebuild which included new valves and guides I am suffering from excessive oil smoking from the exhaust with oil also seeping from the exhaust pipe where it enters the head. (Only 100 miles run so far).The spark plug is running clean and the inlet oil supply needle is set to min. Excessive oil would appear to seeping down the ex valve guide when the engine starts to warm up and be carried out with the exhaust. I have checked the old removed ex guide and found the milled channel carboned up from years of running with only the drilled oil holes free. (The old engine burnt little oil.) Can anyone help? Do I have to hope the carbon will build up to self restrict.

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250 G2 1960 - OVER OILING

Postby Ian5913 » Tue Feb 20, 2001 12:54 pm

Brian

A couple of things to try if you haven't already-
1/
Check the piston rings are correctly fitted..They should say TOP.
This can have the effect your stating
2/
You should have an ajustment screw on the head just by the rocker cover to adjust oil flow to the inlet valve If this is open to far again high smoke and oil useage occur. The correct ajustment is screw it in until stopped then unscrew the smallest amount possible and lock with lock nut. And it means the smallest amount.
(If the valve runs dry it will squeak )

3/
The correct ring gap is .008" to .013"

4/ Worn Valve stems

If you find anything else please let me know!

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250 G2 1960 - OVER OILING

Postby Brian Hebditch » Tue Feb 20, 2001 9:15 pm

Ian,
Thanks for reply. I have already checked items and valves and guides are new. I have come to the conclusion the oil flow into the ex valve guide will need restricting if it doesn't coke up sufficient within a few hundred miles as the pre rebuild set up with the old coked up guide worked OK. Cheers.

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250 G2 1960 - OVER OILING

Postby Rohan B. » Wed Feb 21, 2001 2:07 am

Something else to watch for is that when the new guides were pressed in, they were done correctly (head heated, guides chilled). It seems to be extremely common for them to be pressed in cold, which cuts tracks in the guide hole, and allows oil to flow around the OUTSIDE of the guide.

hopethishelps,
Rohan.

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250 G2 1960 - OVER OILING

Postby Brian Hebditch » Wed Feb 21, 2001 11:07 pm

Rohan,
Thanks for reply. I cooked the head and chilled the guide as manual and find only oil coming down the valve stem. Cheers.

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250 G2 1960 - OVER OILING

Postby TommoT » Thu Feb 22, 2001 11:47 am

I am not familiar with the 250 G2 but could it be that oil is building up in the rocker box, due to restricted return flow, allowing it to reach a level where it overflows the guide and seeps down the valve stem? Or perhaps the oil flow to the rocker box is excessive due to restrictions elsewhere in the system. Just a thought.

Hope you find a solution!

Tom M. (TM)
TommoT

Ride Your Motorcycle As If Your Life Depended On It - Cos' It Does!

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250 G2 1960 - OVER OILING

Postby Ian5913 » Sat Feb 24, 2001 3:03 pm

Brian It's just a thought but I wouldn't be tempted to restrict the flow. If all things are as they should beit should be fine or All lightweights would have smoked like old log fires from the factory. Something I know they didn't.




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250 G2 1960 - OVER OILING

Postby Brian Hebditch » Tue Mar 20, 2001 8:55 pm

Thanks for all replies.
I have cut off oil supplies to both In and Ex valves for a couple of minutes and this made no effect on the oil smoking, so back full circle I have stripped down the cylinder.
Even though the spark plug didn't appear oiled up the piston top and head and Ex port were badly coked with burnt oil after only 250 miles since the rebuild. I have checked the rebored barrel with a bore gauge and it is true and within 1/2 thou of the +20 thou spec with a nicely cross hatched hone.
The new piston is a JP Engineering product made in Australia. On checking, the single oil ring is only 1/8 " wide as opposed to the last Hepolite piston which used 5/52" wide single ring. The oil relief work in the JP piston is a simple slot in the ring groove compared to the Hepolite which has extended slots down the skirt and in a earlier version had 10 extra holes below the oil ring groove.
It would seem Hepolite had gone to work on the oil relief area and it worked when I used both previous Hepolite pistons. Even then the factory manual advises using a duraflex multi oil ring if oil consumption is a problem and states after 1962 they were fitted as standard.
I now think machining the piston and trying to find and fit a multi oil ring is my last resort.
After rambling on, does anyone out there use a JP piston in a 250 G2 or knows of a shelf somewhere with +20 thou piston/rings. Bring back Hepolite! (now known as India Pistons apparently)
Brian.

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250 G2 1960 - OVER OILING

Postby TommoT » Tue Apr 03, 2001 9:28 pm

Brian,
it just sprung to mind: have you thought about crankcase pressure. Could it be that pressure is building up in the crankcase, due to a faulty pressure relief valve or whatever controls the pressure in a G2?

I don't think the split piston skirt has anything to do with oil retention, it is there to compensate for piston expansion.

Good luck!

Tom M. (TM)
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250 G2 1960 - OVER OILING

Postby Brian Hebditch » Mon Apr 09, 2001 10:42 pm

Thanks for reply.
I have already run engine stationary with crankcase drain plug out and drip tray (and topping up oil in tank) to test for back pressure to no avail. The latest idea was I had made up segmental oil rings from Cords in Wales (7) but as the JP piston has only a 1/8" groove I only used 3 of the 4 rings as allowed in Chords spec, again to no improvement. The next attempt will be to machine out the groove to 5/32" and fit all 4 rings and drill additional oil relief holes as found on the original BHP pistons. After that I am stuck. I found Cords very helpful.
Brian Hebditch.

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