classic motorcycle forum

Bronze valve guides are well known for causing sticky valve syndrome in the vintage bike world.
Far better to do them in cast iron, like the motorcycling gods commanded !

I bought an old Enfield, in 'good running condition'.
Unknown to me, it was fitted with a new bronze exhaust valve guide - just before the sale.
Ran fine on a few short runs.
On its 1st long run, on a warmish day, the compression suddenly disappeared.
While we were standing around looking at it, there was a huge CLONK.
I'd like to report it then ran fine again.
But it didn't.
Had shed a pushrod (ohv) and despite having a fair toolkit, wasn't sufficient to refit it.
Trailered back home to the workshop, and that elusive 1/8"W spanner was put to good use.
Bit of a ream out, and was good to go ...

Hi RW,
I'll bet that the clutch centre "hub" that sits on the taper has cracked along the edge of the keyway or that it is binding on the sliding plate
A better method in my opinion of setting up the pressure plate lift is to measure the plate lift near each of the spring nuts using a dial gauge. These clutches do not run very true as they are all well worn by now, so trueing the pressure plate gives a false set up

John

Years ago had that issue with my 1926 Matchless. Took months to track down a sticky exhaust valve that would stop the engine as soon as it got faintly sticky then free up when cooled down.
You show a rather black and oily sparkplug so you may have a similar problem, particularly if you have bronze valve guides. Sorry I don't really follow four stroke threads so you may have already gone through this.
Cheers,

Good call. I've had a new valve guide pick up enough to grip the valve stem. Can you hear any chuff-chuff noises through the carb or silencer when it's kicked over?

Pride, as they say... Cometh before a fall.


I'd been quite chuffed with myself for the way things were going on the bike, so naturally it couldn't last.

Took it out for a longer ride to see how it behaved over 20 or 30 miles of continuous riding, not straying too far from home, riding around the local roads.   At first everything was tickty-boo, it loped along nicely, albeit the fuelling at low revs wasn't perfect: couple of backfires, but nothing worrying at all. Riding "at speed" was fine (tyre pressures were a tad low) but the engine felt good. Clutch and gearchanges were fine (even getting into first at standstill was a lot easier)

Then, while tazzing along nicely it suddenly just went "bleaerrrrrrrrrrrrrrrrrrrrrrrrrrr" and died.  I was on a quiet country road, and luckily a largeish driveway appeared so I rolled into that, safely off the road and stopped.

There was some swearing.

I pulled out the tools and checked the plug: Bit oily, but not overly so - running a tad rich I'd say. (and rolling off tests were indicating that too)


Yes there's sparks.  Yes there's petrol, yes the petrol is flowing into the carb.  Then when trying to kick it... I realised there was absolutely no compression whatsoever.  There is exactly the resistance on the kickstart that indicates the engine is turning over, (ie, it's not clutch slip) but no compression. In addition the head gasket wasn't "puffing" at all which would indicate failure of the gasket. (and there's no marking or blow-by staining to indicate gasket failure)

There was more swearing.

That's not a roadside fix.

I've broken down in worse places, and in worse conditions:




The fork weep is back...


Attempted artsy photo by headlight!




5 hours later:


Eventually got home at about midnight and threw the bike back in the workshop.

Mileage on the odo when I left:


Odo reading at breakdown:  It did nigh on exactly 30 miles!


Reference odo (from after approx 10-15 miles earlier this year)


so - it's done roughly 150 miles on this engine build...  :wtf: 

Still - more than I've done on either of the BMWs this year! :wtf:


Current thinking is the lack of compression is one of the following:
Burnt out valve - maybe that exhaust valve seat wasn't as ground in as well as possible?
Holed piston - messy
Failed piston ring  - that'll do the bore no end of good.
Valve-springs failure - outsider in terms of likelihood, but it would create the symptom.

I won't know until I get in there properly.   The "silver-lining" is that none of it is scary stuff any more and I feel more confident about figuring it out.

However - there's other projects that need to be done, so I'm going to park the JAPton for a month or so and get one or two other projects worked on.

Well - I needed something to keep me busy over winter....  :roll: