500 head queries

Paul Marx

Paul Marx

Hero member
Location
France
Now that I've got the SF2 charging issue sorted, I'm looking into Corinne's 500 which is making an irregular ticking noise from the top end. We're off to central France in a month and now that all the problems of the 500 are sorted, notably thanks to an all new ignition from Sachse with coils from PVL, Corinne would like to take her 500 to show her 650 Bonneville riding friend what it's all about.

I've torqued the head down and will start with valve clearances.
The workshop manual says to measure clearances at TDC, PM mark. However, in that position, the cam tip isn't directly opposite the bucket which is the position I use for measuring usually.
Should I go by the book?

Paul
 
Paul,

The base circle of the cam generally comprises of at least the "lower" 180° of the lobe. It should be completely irrelevant exactly where on the base circle is measured. Care must be taken with cams that have had their lift "optimised" by reducing base circle diameter, without knowing exactly how the cam has been ground and where the lobe begins, it's safer just to stick the lobe tip at 180° from the tappet centre.

piet
 
sfcpiet said:
Paul,

The base circle of the cam generally comprises of at least the "lower" 180° of the lobe. It should be completely irrelevant exactly where on the base circle is measured. Care must be taken with cams that have had their lift "optimised" by reducing base circle diameter, without knowing exactly how the cam has been ground and where the lobe begins, it's safer just to stick the lobe tip at 180° from the tappet centre.

piet
Click to expand...
Thanks, confirms what I thought.
Clearances have closed up quite a bit on the left hand side. 0.12 and 0.13 on the intakes and 0.15 and 0.18 on the exhausts, left hand side. So, off with the cams.
Paul
 
Been delving into the head on Corinnes 500.
The valve clearances measured up as follows:
left intake 0.12 and 0.13, left exhaust 0.15 and 0.18
right intake 0.15 and 0.15
right exhaust 0.20 and 0.18
Nothing catastrophic apart from left hand exhaust. The seats had been recut when the clearances were set, so I'm not too worried.
The camshafts are running on plain scrolled alloy bushes we fitted after turning down the ends of the shafts and press fitting on there hardened steel sleeves.
The bushes are blocked as far as rotation is concerned by a recessed "ledge" on which abutts the cam cap locking plate.
The bushes have obviously moved in the cam caps on the intake cam, they are slightly polished on their outer faces as are the inside of the caps. The "ledge" of the alloy bush shows signs of it hitting the locking plate either side. That may well explain the very intermittent ticking coming from the top, sometimes on a cold engine, sometimes a hot one.
I've no idea why this has occurred.
Now to hunt around my limited stock of 500 valve shims.
Paul
 
You can fit Zane shims to a 500, but not the other way around, Zane spring collar has less clearance.

A drop of medium strength Loctite will hold the cam bushes in place.

piet
 
sfcpiet said:
You can fit Zane shims to a 500, but not the other way around, Zane spring collar has less clearance.

A drop of medium strength Loctite will hold the cam bushes in place.

piet
Click to expand...
I was thinking if I can't obtain new bushes of using Loctite 638.
Paul
 
I received 1m of 1.2mm piano wire in the post this morning, I don't have a piano so in the meantime I'll use some to block the side plate on the split link of the 500 cam chain. Thanks Piet for the tip.
1755785026268.jpeg

You can see how the plate on the cam bush cap stop's it from moving and how this one has been moving, the alloy bush is a bit chewed up. Both intake cam bushes are like that. I should think that would explain the intermittent ticking from the top end.

1755785156054.jpeg

You can also see traces of mouvement on both the bush and the cap. I believe the cause to be an insufficiently torqued down head. There will be 638 Loctite between bushes and caps on rebuild.

1755785258479.jpeg

Paul
 
I use a centre punch placed in the little centre recess of the shim. If they have one. All my triple shims seem to have it.
Pushing down in the centre insures even pressure on the surface. Lap them on a diamond stone.
 
Received the bushes from Australia this morning. Many thanks to Red and Max.
You can clearly see how the bush fitted was trying to turn but couldn't, instead knocking on the cam cap holder. The likely source of the intermittent ticking sound.
As soon as I receive a stock of valve shims, I'll get back to rebuilding that top end so that Corinne can put some km on it before heading South. Valve caps and bushes will be mated with a dab of bearing glue.

In the meantime, the S clutch is out again to cure both slipping and drag and hopefully head South as well.

Paul

1756295918781.jpeg
 
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All done, cams back on and head torqued down; twice.
I measured the valve clearances. Exhaust side is perfect with a loose 0.2mm, however, intake side is a bit loose, a 0.2 shim slides in on a couple of valves.
Your opinion: should I get back in there and tighten up the intake side or leave it be?

Paul
 
Leave it be Paul.

0.20-0.25mm on intake is perfectly acceptable. I'd be far more worried the exhaust being too tight, 0.25-0.30mm is what I aim for.

piet
 
sfcpiet said:
Leave it be Paul.

0.20-0.25mm on intake is perfectly acceptable. I'd be far more worried the exhaust being too tight, 0.25-0.30mm is what I aim for.

piet
Click to expand...
Thanks a lot Piet.
I'll be a bit more precise with my measures and see exactly what I have.
Paul
 
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