Smoking

[Colsbeeza]

My 1961 GF is on second oversize bore, and the LHS cylinder has been blowing smoke since startup after assembly. The guy who did the work assured me that he didn't crack the rings. The bike has only done 40 miles, so I was a little relaxed until now. However, that should be quite enough time to have reduced the smoke considerably. But No.! It blows clouds just after starting (every time), and does not completely go away.
Presumably CR should be about 7.5:1 wit the oversize and the Compression Tester should reach about 110 psig + a little for adiabatic heating.
I used my Compression tester today, and got 85psig on the Left, and 100psig on the right. After adding a few squirts of oil down the bores, the numbers changed to 120 Left and 115 Right. The Wet readings seem OK.
All this suggests that the LHS rings were cracked indeed, but the valves are probably OK.
My next job will be to pull off the head and barrels and take a Bo-Peep, being careful not to drop bits of ring down the crankcase. I will also deglaze the bores lightly if needed, as the RHS dry test may indicate that it is needed.
I have ordered a Leakdown Tester, but it seems that the Compression test has told me mostly what I needed to know.
One thing I do know - No one works on my bike except me from now on.!
Any further thoughts appreciated.!
Col

[coater87]

Hello CB,

 My motor has about 30 miles on it and still smokes out of the left side.

 I will run to 100 at least and see if it clears up slowly before I get too excited.

 I install the pistons in the cylinders, then  install the wrist pins in the pistons. My odds of breaking a ring are tiny.

 30 or 40 miles is not much on fresh rings and bores while trying to seat, and it sounds like we both break a motor in pretty gently.

 Lee

[Triton Thrasher]

I tested mine recently and got a reading of 170psi on both cylinders.
Initially id id it with the throttle shut getting a reading of 130 but was told I should have the throttle open whilst testing compression.
Cheers,
Iain

170 psi sounds like a set of rings that have seated properly.

[Colsbeeza]

G'Day Lee,
I like the idea of putting pins in after pistons.
The smoke is way too heavy for me, so I will pull it down anyway.
I have done a few rebores & new pistons on various bikes & cars over the years but never had much smoke.
With Hondas, I would use pistons which were worn out of spec, but a hone and new rings never gave me problems.
Col

[BSA_54A10]

Individual readings are not much use unless you get a reading under 50 psi.
What is important is a set of readings over time so you can plot the wear in the rings & bore
Even better is a set of wet & dry readings.
When we ran the SR500's for work, they got a monthly measurement.
While the motor would happily run down to 95 psi then object all the way down to 70.
If the rings got done when it had dropped to 120 ( or less ) we could get 3 or 4 sets of rings out of the bore.
If left to much less it was rebore & new piston time

Also the actual number will vary according to the type of meter, type of connection , the rubber hose is always 10%  lower than the solid tube and the quality of the tool.
So a set with the same meter is the go.
A fun game is to get 10 different people to test the same engine, even using the same meter 1/2 of them will be different.
Unfortunately the calculator/computer age has causes way to much empathsis on the actual number and not the trend

[JulianS]

What make of rings were used?

The "new" hepolite branded ones have a bad reputation for quality. If you have those fitted that may be the cause of your problem.

[Colsbeeza]

Thanks Trev, That seems a great strategy to lengthen the life of the bores, and it does emphasise the problem of running too long with low compression. I don't think I have the luxury of monitoring it over time just yet. The readings explain the severe smoking. I am not prepared to ride it for another 100 miles or so and then discover it has broken rings or something else. I don't want to risk further damage and I wouldn't enjoy the riding anyway. The thought of thick carbon jamming up and down on my new bores leaves me cold. ( a vivid imagination can be a curse at times ) Best I find out now, fix it and enjoy the running in.
In 1980 I purchased a new Chrysler Sigma wagon when the first baby was born. It burnt oil for 186,000 Km. Of course, the company said that 1 liter loss per 1000Km was within the normal range. I found out it had chromed rings and Nikasil bores, so it was never going to bed in - not with my driving style anyway. The pistons took me hours to clean up. I honed the bores and fitted cast iron rings for a total cost of A$114. It never burnt a drop of oil thereafter, even from the first day.
Julian the rings were Hepolite but purchased about 25 years ago. I still have / had the box until recently, but a scrounge in my shed just now has not turned it up. Presumably the Chinese were not making them ten.?
Can you suggest a source and brand of good quality rings.?
Cheers
Col

[BSA_54A10]

Col,
I have been using dry fitted rings now for around 20 years and can thoroughly recommend doing it that way.
Musky fits his dry as well.
Running in consists of one lap of the block, about 3/4 mile.
What kills rebores is starting the engine then frigging around for 20 minutes with the engine idleing as you attempt to adjust the carb.
After a couple of minutes of no load running the bore has already started to glaze.

So it is on with the riding gear kick / push start, starting fluid, whatever it takes then a hard run around the block with lots of wide open throttle up & down through the gears.
After that back in the shed for a cool down & retorque then around the block a second time , then back to the shed to do the tuning.

It should have been self evident to e that it was a waste of time trying to adjust a carb on an engine which was yet to seat the rings fully, but I am a slow learner.
I wipe the bore with an oily rag then wipe off with a dry one, wind the pistons into the barrels, tighten the flange bolts then off down the road

[ellis]

I recently fitted a set of GANDINI rings to the 850 commando and was very pleased with the results. No smoke and did a few full throttle runs to bed them in but kept the tacho below four thousand with good results.   

ELLIS

[RichardL]

After that back in the shed for a cool down & retorque then around the block a second time , then back to the shed to do the tuning.

This is where you lose me. Seems a liitle item like removing and replacing the rocker box is omitted from this fun afternoon.

Richard L.

[berger]

yes ellis I love gandinis , I've had rings that were shaped like 50p pieces that chucked neat oil out the exhausts. I blued the bores and pushed the rings up them and saw horrors of hit and miss contact. they were thrown over the shoulder and gandinis fitted , started the bike and not one bit of smoke

[trevinoz]

And don't get it honed too fine.

[BSA_54A10]

After that back in the shed for a cool down & retorque then around the block a second time , then back to the shed to do the tuning.

This is where you lose me. Seems a liitle item like removing and replacing the rocker box is omitted from this fun afternoon.

Richard L.

Yet to find a way to access the head bolts with the rocker box on, but am all ears if you know one.
And FWIW the new rocker box gaskets ( if they are going to be fitted ) go on after the final torque down and yes it is a full day job.
One reason why to a large part I have given up on motorcycles with 1 or 2 redundant cylinders.

[Colsbeeza]

Trev,
I think that frigging round has been my problem. Not my fault though.
I took the cylinders off yesterday. A quick inspection hasn't thrown up a reason. The bores and rings look good (none broken) and the bore cross-hatching is quite visible all round. The little-end bearings had been machined with tight tolerance to the gudgeon pins, and the pistons still did not rock back and forth without a little help yesterday. I will get the pistons off and have a good inspection over next few days though, as the rear of both pistons have lost their "frosty" or matt finish for a width of about 0.5 - 1cm  below the rings and are shiny in that spot. That may be normal?, or could that be due to the firm gudgeon pins?. I had also best replace the rings. Do you know where I can get Gandini rings.? A quick search on the internet hasn't solved that for me that yet. Not sure I should trust modern Hepolites from what I read on the Forum. Any other ring recommendations for a bog-standard GF which will not be raced, but will be a gentleman's tourer for Club events.??
Anyway re the frigging around - When the bike was first run back in November 2016, it blew smoke from the left cylinder and I guess were possibly not glazed at that stage. It had probably been started a few times in the workshop (not by me). I had some months earlier had the magneto checked. I then spent a year doing the wiring from scratch amongst other competing pressures ( I am not an electrician ), and all the other fiddly bits to get it running. When I eventually started it in October 2017, the bike was spitting badly, and would not rev. The left exhaust pipe was glowing red within a few minutes. After a few weeks of persisting and checking carb, timing, tappets and anything else that moves and starting it many times, I had the magneto rechecked again as a last resort. Yep it was out by many degrees - not explainable. This time I went to Sydney to pick it up and got to watch the magneto perform on the tester, and it was then firing within a half degree between cylinders consistently with good spark. 
To cut a long story short, the bike was probably started 30 or 40 times before I could get it on the road for a blast.  I was certainly aware of glazing bores but could not do anything about it. That is where I am at the moment.
Is that enough to explain the 85psi dry compression test on the left, and 100 on the right, and 120 left wet and 115 right wet.?? (
I think I may go down the path of dry rings, given that the rest of the motor has 40 miles on it. By that I hope you mean to assemble the pistons & rings without oil, but the circulating oil system as normal.? Just give it a blast before the rings get wet.?
Whilst I have it down, I will go through the many other possibilities I have not already dismissed. It does not wet sump, the tank breather is not blocked, I am using a 20W-60 mineral oil without friction-modifying additives. It has an external oil filter correctly connected. I had set the timing at 32 Deg BTDC, and I will retard that a bit to about 30 Deg to suit modern fuel. After all it is a bog standard 1961 GF.
I will also check the breather passage from the timing side. I am not sure of the status of the cork breather seal thickness. I will also remove the oil pump and check the gaskets. And Trev (inoz), I will give the bores another hone to clear the glazing.
That all sound good.??
Col

[Colsbeeza]

Well I got the Flash back together after getting the guides replaced, faced the head, checked for cracks, freed up the little-end bushes which were too tight, de-glazed the bores, replaced the rings, and took it for a 5-mile run - fairly hard but variable. Since it had already done 40 miles, I extended this run a little. Good power, no unusual noises, pleasant to ride. The Clutch is getting a little stubborn though.
It is still smoking on the LHS much as before, although only one run. So I have come up with my strategy list of things to eliminate. My main suspicion is the breather system - perhaps worn cork or blockage, although piston/ring match can be a headache.
All the costly ones are done, but given what I found inside, I was too smuggly confident to complete the obvious things.
It will be a few weeks before I can get this done, as well as re-tensioning the cylinder base nuts and head bolts but any  additional ideas would be appreciated. BTW the pistons are 25yo Hepolites with only 40 miles on them. The new rings are AE Hepolite from SRM.
Cheers
Col