"F" cylinder wall mark

[Ian.Taylor]

Last year while on a very Hot summer evening my F tightened up about 3 times.
Once back home the cylinder & piston was removed and checked.
The clearance was .0035 .
This was done by the shop in the 80's when a new liner was installed.

My friend who has the proper machine to hone did mine for me and check for Taper etc.
he set the clearance to .0055 .New rings from cox & Turner were installed and all was good.
No more burning oil.This year was the same until about 100 miles ago when I noticed smoke roughly 20 sec after start up .Once underway it diminished .
Now it seems to be smoking longer and a a little more while riding.Mind you oil consumption hasn't gone down that much but still a concern.
Today I removed the barrel and for some reason it was a tad tight at the very bottom.

As you can see from the photo the mark in the cylinder wall is in exactly the same position on the opposite side .
The photo of the piston you can clearly see rubbing marks on the piston.
Not so much on the left side.
Any idea what caused this?

The other question,while I have it apart ,can I drill 4 or 5 small holes where the screw driver points ( front & rear ) to help rid of oil?

The other option is to drill the lower ring groove and install an oil control ring then add oil to the gas.my last resort.
I would like to keep the original ring set up.

Other than that the bike runs great,very smooth and pulls past 55mph no problem.

[PeterW]

I'd guess the rings are jamming in the grooves, that would account for the if they are jamming out at the sides and the smoke as then they'd be right in front & back.
Or maybe the bore is oval and the piston isn't?

[john.whiting]

The mark is quite deep,as the recent hone hasnt touched it.It looks like rings fitted with insufficient gap,causing breakage,or rings fitted into carboned grooves,or fitted into grooves too shallow for the ring section.There is definitely a significant piece out of the liner surface.remove and check your rings ,especially for groove depth,as the piston is out.You know that you cant fit slotted or rail oil rings with open valves.If the rings are free,and can be pushed below the piston surface,and have enough gap,then they are OK to go.Also check that the piston has some side to side clearance on the small end .If not,produce some with a Dremel,or the like.Also check that the flywheels arent off centre in the cases.The other possibility is that the liner wasnt installed correctly,and is not square to the flange.(This is not uncommon in an old single).

[Ian.Taylor]

Thanks guys
When the cylinder was honed the mechanic ( my friend) checked for taper and the cylinder was round.
The marks you see came later after maybe 200 or so miles . The rod is center and the piston has side play .
Since after the hone & new rings it didn't smoke at all until this year.
Because i use a high quality oil..Kendal 50w with titanium this may have cause the rings NOT to seat. as has been suggested and what I have been reading on the internet.

I am puzzled though by the 2 marks on the cylinder.
Rings are free and the gap is .012 . they sit correctly in the ring groove.
I'll keep checking things out.

[Ian.Taylor]

Today i removed the piston just to check fit in the Bore.I discovered the small end Bushing in the rod is slightly loose and does move .
I'm thinking of having it knurled and re fit with loctite
Unless someone is making them I'm not aware of.
Also found out the oil I was using was a semi synthetic , not good for break in.

[paul.jameson]

I am assuming (but I may be on the wrong track altogether) that the mark is made by the centre line of the pad at the end of the gudgeon pin, in which case, simply lapping in the two pads with something like solvol autosol should solve the problem.
As to drilling holes where your screwdriver point is; it seems to me that those holes may be more designed to increase the amount of oil on the cylinder bore than to remove it. As the big end rotates and oil is flung from it, the oil must go up the inside of the piston far more than up the wall of the cylinder, particularly towards the top, since this is shielded by the piston skirt.

[Brian.Fosh]

I struggled similarly with a BSA sloper regularly seizing after initial rebuild, despite original bore and piston.
Running richer really helped. e.g a slide with a 1/16" less cutaway.
I liked the Brass carb so persevered but I have heard only good things from people fitting newly-made Amals.
After initial investigations like yourself, I went on to make very many long Motorway trips to Belguim, the TT and south coast... much of it on the motorway, e.g M11, M25 etc to Dover, M1/M6 to Heysham etc.

Best of luck

Brian.

[Ian.Taylor]

Hi Paul
My first thought was the pads made the marks but when the barrel was removed it was clear the pads had NOT moved at all and were still behind the skirt of the piston .
The square mark looks like the side of the piston where the pin is located No where else on the cyclinder wall. weird.
Thanks for the info on the holes ,here I thought these were to help drain oil away. I`ll leave well alone.
I have found a machinist who will make a new small end bushing but need to take the crank in,so motor will come apart.

The oil I used was Kendal 50w with titanium high performance oil. It seems this is a semi synthetic which I think may have cause the rings not to seal during break in.`

Having worked most of the bugs out ,this 31 is really a nice bike to ride.
I`m hoping this will be the final issue.

So far the carb I have on it seems to be working good.
The only change I might make is going up from the 170 main to a 180 as Ariel sugessted 170 or 180 for the `F`s

[nevhunter]

You are getting the piston clearances a bit on the low side. That piston has no slots and if you read the makers recommendations they need a lot more than 5.5 thou to be safe. Earlier alloys are often what is called "Y" alloy which was a high strength alloy used in aircraft engines in the late 20's It doesn't have silicon in it and expands a bit more than some modern pistons especially Japanese ones that are high silicon. Also the wide rings often have a bit of trouble sealing. You would be better to use two in each groove. More expensive but better result. end gap minimum .010" at installation and stagger the gaps.
Relieving under the bottom groove is normal procedure in the late 20's on. Just about every maker used it. I don't have oil rings in any of my Ariels before the larger pump was fitted, and with the small pump none of them smoke if the rings are good. I would say they (yours) have distorted. You should be able to fit the new bush to the rod eye without dismantling if you have a threaded inserter/ remover designed for the job. Note how tight the old bush press fit is in the rod and adjust the new one accordingly. You might have to ease a bit out with an adjustable reamer if it ends up a bit tight after pressing in. Prevent metal entering the case while this is done with a rag. A long threaded stud with suitable sleeves and nuts will extract and insert the bush.. Check for rod straightness after fitting by tilting the barrel towards each side before tightening the hold down nuts. Don't force it and you should get an equal gap each side or place 1" square bars under the skirt of the piston on the face of the crankcase and check both sides of the piston skirt contact evenly . Nev

[Ian.Taylor]

Thanks Nev
Question on Piston & ring Gap clearance.
I'm sure Ariel recommended .005-.007.
At what clearance do you recommend Nev?
Ariel gave .006-.008 for ring end gap ,your recommending .010 as a min Gap
Are you finding the .006-008 too tight when the motor is hot?
Ian