I think it might be time for a..

[Bazil]

Top end refresh on my Mark IV Lemans ?

Did a compression check on the weekend, plugs out, wide open throttle.

Left hand side 125 psi. Right hand side 125 psi.
Added 15 mil or so of oil down the plug holes  and got:

left hand side 150 psi, right hand side 150 psi.

At least it's consistent.

Looks like at least new rings are called for.

Two questions :

1. Those figures look bad, but it's just coming in to riding season down here and I'd rather ride than wrench. Do I just hold off until winter is creeping up on me, or should I dive in now ? Am I doing any damage by continuing to ride in it's current condition?

2. While it's pulled down, should I get valves guides  K lined and valves re-ground ? Big blocks have a reputation for being hard on valves and Gina has 50 thousand kays on her. My thought is to just do it while heads are off regardless.

Your comments gratefully received

Cheers

Bazil

[Muzz]

The 15ml of oil will bring it up all by itself, let alone sealing the rings.

At 125 I would just ride it. 50,000 kms is not that much.

[jacksonracingcomau]

The 15ml of oil will bring it up all by itself, let alone sealing the rings.

At 125 I would just ride it. 50,000 kms is not that much.

 :1:


1/ Was comp check hot ? makes the world of difference
2/ Why are you even checking it ?

Start with the "problem" symptoms, work from there, if you have a fuel or oil consumption problem might be much easier to diagnose.
If you do take it apart, measure everything before blindly changing anything, if rings are shagged at that mileage, you want to know why.
Colour of piston crowns/ cylinder heads will tell a story.
Easy check for guides is when it blows smoke, under power--rings, at gear changes--guides.
Look down inlet ports at valve stem, do you have build up of carbon ?

[LeRoy]

Was there a problem that lead you to do the compression check? ...excessive oil consumption or smoke? ...poor power? Unless you have symptoms of a problem I wouldn't take things apart.

While it's true that the big valve engine in your bike is hard on its valve guides, 50,000 km isn't all that much unless the bike has led a hard life, has been run without good air filtration or has been poorly maintained. Some are shagged at that point, many are not. Do you know the bike's history? If the bike was consistently flogged it might well need valve and ring work. If it's led an easier life it probably still shows greater than a more sedately tuned bike, but may well not need urgent work.

If it was mine (and I do own one just like it), I'd ride it in the coming season, keep an eye on things like oil consumption and smoke, and -- if warranted -- plan on a top-end rebuild in the next off-season.

As to what you should be prepared to do if top-end work is indicated, I'd expect that a set of rings would be called for, but I'd be surprised if a re-bore was necessary. Close measurement on tear-down will tell the tale. I'd also expect that new valves and guides would be wise while it's down. K-lining is a good alternative on the guides. A general clean-up of the combustion chamber is obvious, plus new head gaskets, O-rings and other consumables. Take a look at the oil passages in the rockers to be sure they're clear. Look for wear on the rocker faces and peak down the tappet bores to look at the cam lobes. And, while it's apart, you can easily check the rod bearings and swap in a new set if called for. All of this can be done with the engine in the frame. The tear-down in an easy afternoon's work; the reassembly about the same. You'll spend most of your time cleaning parts and waiting for specialists to re-do things like the valve guides.

[Tom]

Are you making a comparison of performance vs other brand bikes?  When you're riding it....what rev's are you shifting gears?  Should be above 4K rpm's.  5K would be better.

[Bazil]

Thanks all for your comments - maybe I'm making a mountain out of a molehill.

Reason for the compression check was because it blowing a bit of smoke at idle,  more on the left than the right side, and a handful of throttle while stationary would produce of a bit more smoke. Fuel consumption has never been great either. Plugs are sooty, though I haven't done a plug chop, only pulled them after a run. I'm running the ed milch carb setup, but with AB 268 atomisers at the moment. Engine is stock, but with pod filters and La Franconi mufflers. I don't know the bikes history unfortunately.

Compression check was with a cold engine.

Thanks for the tip which points to whether it's guides or rings Martin, I'll check that out, along with peering down the valve stems.

I'd always be shifting above 4000 rpm, generally I keep revs between 4000 and 5500, unless it's just legal speed highway cruising when it's a bit lower, or if I'm feeling enthusiastic, when it's a bit higher.

As suggested by all here, i'll just monitor for the moment with a view to doing something if I think it's warranted when the sun stops shining and it's getting cold.

Performance comparison vs. other brand bikes ? No point - it would be like comparing a CNC mill to an anvil !

Thanks everyone

Bazil

[Tom]

The rings may be sticking a little.  If you have Marvel Mystery Oil down there.  Add to your gas.  My '80 SP1000NT will burn a little oil on the left cylinder on start.  This bike sits most of the year and I use only for touring rides during the summer.  I've also used in my Eldrorado when the left cylinder was doing the same slight oil burn.