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British Bikes / Re: Troubleshooting a JAP Special
« Last post by Rockburner on November 10, 2026, 09:05:10 PM »
Well - the JAPton is back on the ramp.

Still no idea what's happened to the compression as yet, but I've started stripping it down.

Head steady rotated out of the way and the carb off.


Just gaining access at this point.


Took the pipe off all in one go - the nut at the exhaust manifold was tight as f***.  I know I did it up "tight"... but not THAT tight!  Good thing I had an extension bar...  I also remembered to use some neoprene to protect the nut this time! :D


I was then going around the engine getting the engine bolts undone when I smacked my head on the sodding kick-start lever.  Which I decided was a good time to head in and enjoy the rest of the evening in peace...

More to come.
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British Bikes / Re: My 1951 G2 Trials
« Last post by murdo on October 22, 2026, 09:12:01 PM »
Using my gas BBQ I took the head casting to about 180 deg (might have cooled a little by the time I got it on the wooden blocks) and only took two light taps to remove old guides and three to seat the new ones. The guides needed a light touch with a reamer after cooling down to get a nice sliding fit, but the exhaust was a little off centre when I put some bearing blue on the valve and fitted in the seat. Took a bit with the stones to get straight, the intake was good. Ended up with good seal and seat widths.
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British Bikes / Re: My 1951 G2 Trials
« Last post by cardan on October 21, 2026, 11:58:11 PM »
Slow heating in the oven, for caution...

Best also to do some careful measuring to asses the level of interference of the fit. I'm not sure exactly what is should be - look it up - but it's only small - I doubt it's more than 0.001" or so. It would be a pity to heat your head, cool your guides, and still find the things stuck half-way in!!

Leon
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British Bikes / Re: My 1951 G2 Trials
« Last post by R on October 21, 2026, 10:34:02 PM »
For fitting bearings (into the crankcase) the traditional quote was to get it hot enough
"that when you spit on it, it spits back at you" 

I'd think that alloy cyl heads would need to be at least this hot.
The last thing you want to do is split something in half because it wasn't hot enough.

AI suggests a broad range of 150 C  ++

Aluminium melts at a (moderately) lowish temp, with about zero warning, so don't overdo it !  (oxy torch, etc).
You don't want to soften or warp it either.
Chilling the new guides assists a little also.
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British Bikes / Re: My 1951 G2 Trials
« Last post by murdo on October 21, 2026, 09:22:00 PM »
Have put aside the oil feed to head problem for the moment. I need to replace the valve guides and have new ones to hand and have made tools to do the job, but I am wondering what temp I should bring the head to before picking up the hammer. The vintage motorcyclist book doesnt mention a temp for this job. Any suggestions?
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British Bikes / Re: My 1951 G2 Trials
« Last post by murdo on October 13, 2026, 09:55:00 PM »
Quote from: Vreagh on October 13, 2026, 10:59:14 AM
Have you checked the pressure relief valve in the crankcase ?
Yes as described above, the ball is seated correctly and can feel it relieve the pressure when pumping hard with oil can. The oil feed to the rockers is showing no sign of any oil at the crankcase fitting.
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British Bikes / Re: My 1951 G2 Trials
« Last post by Vreagh on October 13, 2026, 10:59:14 AM »
I think he's referring to the rockers feed which of course are plain bearings. Have you checked the pressure relief valve in the crankcase ?
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British Bikes / Re: My 1951 G2 Trials
« Last post by Rex on October 13, 2026, 09:13:01 AM »
if the pumps are present and pumping and the oil drillings are clear what's the issue? I've always been surprised at the simplicity of Enfield pumps and oil systems, so maybe you're looking into it too deeply?
They're ball/roller bearings so run on a smear of oil at no pressure.
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British Bikes / Re: My 1951 G2 Trials
« Last post by murdo on October 13, 2026, 07:46:17 AM »
Things havent progressed much while I have been in hospital but I am able to do small things that dont involve lifting ok. Today I filled the oil tank and spun the engine over with battery drill (no cylinder head on yet) to get oil pressure up. I have good flow to the crank and return to tank, but cannot get any oil from the fitting that the cylinder head pipe attaches to.
For those not familiar with Royal Enfields, the head oil supply comes from the scavange pump side and is pushed through the timing case to passages in the crankcase and up to the head through an external pipe.
Today I took the timing cover off and rechecked all the passages and that the relief valve was seated correctly. Using an oil can was able to push oil through all the passages and could feel the relief valve open when pumping hard with the oil can. By turning the oil pump shaft by hand was able to get oil flowing, so I know that the pumps are working fine.
Could the problem be that the drill is not turning the engine (and therefore pumps) fast enough to get the oil to flow?
I hope some of you wiser gentlemen may be able to suggest where I can go from here as I have no wish to start the engine with no oil flow.
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British Bikes / Re: Australian-made motorcycles in the 1950s - help please
« Last post by R on October 07, 2026, 11:29:02 AM »
My little Waratah spent its entire life on a farm, going to check on the cattle every morning.

When it was about worn out, it was replaced - by a CL175. Circa 1971 I think.
I bought it at the farm clearing sale, one owner, never been off the farm.
It still ran, but the teeth were nearly entirely worn off the gearbox sprocket.
And the big end talked to you
Probably never had a penny spent on it ...
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