Do I need a refresh?

[Howard]

Kenny, I wish my Comet looked that good inside. It looks like a lot of expensive recent work has been done. Only "obvious" ways to burn oil are past rings or guides, but from the photos I suspect yours will be good enough not to do this. I'd look at the breather, if that's not timed right the extra crankcase pressure could be "forcing" oil past rings or guides.

Give the cylinder oil hole a second (or third) measure, I had that trouble for some time before I found it, and it's really not obvious at a glance.

H

 

[KennyNUT]

Howard,

I came across this:

http://www.voc.uk.com/net/docs/3.5f/3.5-608-17.pdf

an apparent quick fix where the pistons (twin) are positioned to bottom dead centre and the timing chest cover removed, the breather gear is pulled out of its mating position, turned anti-clockwise by two teeth, pushed back in and the case re-assembled. Its called Busby's Breather Breakthrough (BBB) and its in MPH edition, #608, page 17. It sounds too easy! Especially, as Martyn in post #40 describes something much more elaborate.

There are other follow up points that also discuss a Breather Cap, used in series D.

If Simon says the head is spot on and he has already said piston and liner look like new, is there too much pressure in the crankcase as per Martyn's learning's earlier, pushing oil past the rings? Should I try the BBB (with the single at BDC) or buy a series D breather cap for additional reduction in crankcase pressure? The Comet already has a case breather off the left hand side of the crankcase just under the float chamber, seen below and it has (another breather) that oils the chain!

I feel I am chasing different things, now.

I don't want to be taking the head off again and again and changing rings, then drilling the piston , then working on the breather.

Another thing that is nagging me is why the exhaust valve looks so sooty (matt black) compared with the inlet valve and the top of the combustion chamber looks so lightly used.

Maybe I should rest up and wait on Simon for a bit in case he finds something in the head components that was not visually obvious !

K.

 

[davidd]

Kenny,

You could have a serious hidden problem, but none to the story and photos point to one. If you had performed a Leak Down test, you would have known before it was dismantled which components were leaking. Having passed on the test, it is now up to visual inspection. My guess is that the rings have failed through improper break in. I would deglaze the cylinder and install new rings. I install them dry, but others can't resist applying oil, but it should be break in oil not engine oil.

I would not worry about the Dick Busby method. If I remember, Neville's article was a response to Dick's method. If I read Martyn correctly, he is following the Neville method, which is, simply stated, checking when the breather opens and closes. His other suggestions are straight from Phil Irving and easy to do with a file, but not the end of the world if you don't. I have found the stock breather to be quite good on a properly built engine.

The carbon should not be a big worry. The intake valve passes a nice cool charge from the carb and is constantly cooled this way. The exhaust is passing very high temperature combusted gases and is mostly cooled by passing heat through the tiny contact ring on the exhaust seat. Thus, it runs much hotter than the intake. So, it will usually have more carbon deposits even in an oily environment.

I broke a compression ring at a race in Texas and when I put the new rings in I deglazed the cylinder with a ball hone and broke it in properly. After three years it is still near new (4% leak down).

David

 

[Martyn Goodwin]

While you have the bike in its current state I would make a very strong recommendation for you to check the camshaft timing - that is when the valves open and close. I ran my Comet for almost 2 years and 10,000 miles before I did this only then to discover that the valve timing was out by a massive 12 degrees. You cannot trust the timing marks! There is a good description of how to do this in PEI's book "Tuning for Speed". Send me a PM if you do not have access to this publication.

While this statement may be disputed by some purists - it is my understanding that what you should be aiming for is to have equal valve lift (inlet and exhaust) at 4 degrees before top dead centre. PEI has said an error of up to 2 degrees is acceptable.

Martyn

 

[nkt267]

seen below and it has (another breather) that oils the chain!

The 'breather' that oils the chain is really the chain oiler, if you are getting too much from there then you can use the screw in the top of the oil tank to reduce it. A lot of riders screw it down tight as on some bikes it never controls the flow to the chain properly.I've removed the pipe completely and blanked the outlet off. John

 

[greg brillus]

The vent on the oil tank that feeds down to the chain is actually a hole on the right side of the steel block that is welded inside the neck of the oil tank spout. It is quite hard to see unless you look closely for it. This vent is always open, the adjuster screw simply lets a metered amount of return oil enter that passageway, and then down to the chain. Unless the tiny hole in your tank cap can vent well enough, blanking off the chain oiler at the rear of the Upper frame will pressurize the oil tank. I originally blanked my oil tank this way too, but once I discovered that the tank cap hole could not keep up, I removed the blank, and opened it again and ran an extension hose to the rear axle, this with a "T" piece coupled to the engine breather.....remember that the scavenge pump is returning at least double the volume of the delivery. Even though most of it is a mix of oil and air, it is still a larger amount than is being taken from the tank. At elevated speeds I no longer get any oil coming out of the tank cap hole........Greg.

 

[KennyNUT]

Thanks gents, for the continued discussion.

I have some news!

Simon Linford called me on Saturday morning (forum was down for maintenance) and told me that everything in the head was like new. He then indicated that the bike's upper cylinder liner looked a little shiny and suggested that this was fuel glazing and a quick deglaze with a glaze-busting hone and new rings and to go through the bedding-in process once again should sort the top end out. Otherwise, he declared the top end sound and suggested the big end was in great shape too as the skirt of the piston was unmarked.

All very honest of him and so this week he is sending barrel, head etc back to me for re-assembly onto the bike.

So on Saturday night, I dug around the files that came with the bike and discovered another file (I did say the bike had heaps of history with it) that indicated the bike engine and other areas of the bike were refreshed again in 1997 and then I reviewed every MOT and tax disc from 1997 to 2005 to determine that the bike has never been run in fully by the former owner! Each year the mileage recorded on the MOT form was between 6 miles in one year (I presume 3 miles is the distance to the MOT centre!) and up to 60 miles per year on occasions adding up to a total of 457 miles up to 2005. After 2005 the bike was not used and I have my notes from the purchase indicating that the previous owner, a Mr Pumford, was a motorcycle mechanic of 30 years+ and through poor health eventually let the bike go. The Comet was sold to me with just over 500 miles on the clock with the seller having performed some electrical and other work to recommission the bike before sale together with a service and MOT along with a 30 mile final test ride before I took delivery.

So that accounts for the clean oil, new piston, head work and everything else inside still like new. The bike has only done a tiny mileage since that original work in 1997. Today I went back to the piston and looked over the rings again (since I have ordered a replacement set from the VOC for re-assembly). I saw the correct oil ways behind the oil control ring, which I didn't see before as I did not play with the rings at all. One thing I did notice is that the oil control ring gap and the central ring gap were in alignment on the thrust face of the piston and I did notice that when I removed the barrel whereas the other gap to the top ring was 180 degrees on the exhaust end of the piston. I thought that was OK at the time, however, having read up a little more (again), I do not believe this to be correct. I do know the rings were not rotated upon inspection by myself and double checked this against an original photograph I took when the barrel was originally slipped off.

In the original picture (above) from when I removed the barrel, you can just make out the dark gap from the middle ring only a few degrees offset from the oil control ring (shiny spring part also just visible). This is exactly how I remember seeing it and rechecked that today as it played on my mind to check the oil ways in the piston.

Was this a small oversight or could it have rotated during installation back in 1997?

Should each ring from the first to last have the gap at 90 degrees apart with no gap above the gudgeon pin side? That is my understanding of correct fitting. I wonder if this accounts for some oil blowback into the combustion chamber?

I know the rings can move from side to side only a tiny bit but only a degree or two, perhaps. They do not twist round during operation.

What do you think?

Regards, Kenny.

 

[Mark Fisher]

Thanks gents, for the continued discussion.

I have some news!

Simon Linford called me on Saturday morning (forum was down for maintenance) and told me that everything in the head was like new. He then indicated that the bike's upper cylinder liner looked a little shiny and suggested that this was fuel glazing and a quick deglaze with a glaze-busting hone and new rings and to go through the bedding-in process once again should sort the top end out. Otherwise, he declared the top end sound and suggested the big end was in great shape too as the skirt of the piston was unmarked.

All very honest of him and so this week he is sending barrel, head etc back to me for re-assembly onto the bike.

So on Saturday night, I dug around the files that came with the bike and discovered another file (I did say the bike had heaps of history with it) that indicated the bike engine and other areas of the bike were refreshed again in 1997 and then I reviewed every MOT and tax disc from 1997 to 2005 to determine that the bike has never been run in fully by the former owner! Each year the mileage recorded on the MOT form was between 6 miles in one year (I presume 3 miles is the distance to the MOT centre!) and up to 60 miles per year on occasions adding up to a total of 457 miles up to 2005. After 2005 the bike was not used and I have my notes from the purchase indicating that the previous owner, a Mr Pumford, was a motorcycle mechanic of 30 years+ and through poor health eventually let the bike go. The Comet was sold to me with just over 500 miles on the clock with the seller having performed some electrical and other work to recommission the bike before sale together with a service and MOT along with a 30 mile final test ride before I took delivery.

So that accounts for the clean oil, new piston, head work and everything else inside still like new. The bike has only done a tiny mileage since that original work in 1997. Today I went back to the piston and looked over the rings again (since I have ordered a replacement set from the VOC for re-assembly). I saw the correct oil ways behind the oil control ring, which I didn't see before as I did not play with the rings at all. One thing I did notice is that the oil control ring gap and the central ring gap were in alignment on the thrust face of the piston and I did notice that when I removed the barrel whereas the other gap to the top ring was 180 degrees on the exhaust end of the piston. I thought that was OK at the time, however, having read up a little more (again), I do not believe this to be correct. I do know the rings were not rotated upon inspection by myself and double checked this against an original photograph I took when the barrel was originally slipped off.

View attachment 3295

In the original picture (above) from when I removed the barrel, you can just make out the dark gap from the middle ring only a few degrees offset from the oil control ring (shiny spring part also just visible). This is exactly how I remember seeing it and rechecked that today as it played on my mind to check the oil ways in the piston.

Was this a small oversight or could it have rotated during installation back in 1997?

Should each ring from the first to last have the gap at 90 degrees apart with no gap above the gudgeon pin side? That is my understanding of correct fitting. I wonder if this accounts for some oil blowback into the combustion chamber?

I know the rings can move from side to side only a tiny bit but only a degree or two, perhaps. They do not twist round during operation.

What do you think?

Regards, Kenny.

Kenny, I think Simon has already diagnosed your issue, (by the way thanks Simon if you're out there , my shadow heads you did for me in 2008 are still doing fine 20k miles later) not running a newly built engine can be a bad thing. I had similar issues with a velo thruxton that the previous owner had spent a fortune on, it smoked and threw oil out into the chaincase and compression was poor, yet all was new. Turns out that the previous owner never actually rode the bike, he just started it up in his garage occasionally. No amount of high speed and variation thru the rev range would get the rings to bed in (seat) properly, so, like you, I had to take a newly rebuilt engine apart! I had the cylinder honed, fitted new rings and assembled piston and cylinder dry. This last step went against all my instincts but I followed David Dunphy's advise and was rewarded with a complete fix of the problem after just a few miles of running on the road. So you are definitely on the right track. Good luck.
mark

 

[KennyNUT]

Mark,

You know when you are thinking something, but would never admit it to anyone as you could not possibly believe it to be correct - ie its not a logical way to think, well you have just confirmed one of those thoughts.

To DavidD, I have read some of your responses and you seem like a gent who knows his stuff but a "dry" re-assembly of the piston and barrel had me completely flummoxed and head scratching to the point I thought you were pulling my leg. You know like the new electrician apprentice who is sent to stores for "a box of sparks"

So it was a great story that you shared, Mark and very brave of you to do this with a Black Shadow engine. Thanks for the reassurance. I hated to think I was that electrical apprentice with my Comet

Anyway, I ordered the new rings yesterday and will buy a ball hone tomorrow from

http://www.pacehigh.co.uk/pages/default.aspx?productID=23955&mode=productDetails

In the meantime, I have new gaskets and have cleaned the oil pump brass screw and will re-assemble that with a little RHODORSIL on the furthest away from the pump threads and pop it back into the crankcase. If I reassemble everything with care, then we hopefully, will be back on track.

Does anyone recommend running in oil or just use standard 40wt. And after how many miles should I change that?

So, I am thinking that my first run should not just be a start up, it should be a proper run with my mobile phone(!), and hopefully, before salt starts being deposited on the roads and the frosts and snow arrives!

Thanks, Kenny.

 

[clevtrev]

Dry assembly means NO oil in the combustion chamber at all. Otherwise the first time the engine fires the oil will glaze on the cylinder wall, and no way will the rings seat. So just lightly oil the skirt below the rings, degrease everything above the oil control ring. For best results a 10W oil will be the way to go, forget using 40W. On start up for the first time, open the throttle, and give it plenty of revs for at least two minutes, it`s the gas pressure that pushes the rings into contact with the bore. As it`s now winter use the 10W for 500 or so miles then change for more 10. After all you don`t want your engine to be glued together, you want it to run freely. And when you do give us some feedback to tell us how warm the oil got.