2021 just like 2020

[Gordon]

Well so far the new year is not going any better than the last year. Worked all day yesterday and I still have the same problem as last year.

I am building the Upshur Twin Horizontal and it does not even try to run. The problem as usual is compression. I have made new pistons and tried new rings. If I put compressed air in the cylinder I am not finding any leaks and there does not seem to be air leaks around the piston. The strange thing is that I seem to have good suction on the intake stroke and almost nothing on the compression stroke. If I put my finger over the spark plug hole it holds suction but almost nothing on the compression stroke. Very minimal air leakage around the valve when using compressed air. That is backwards because under compression the valves should be forced harder against the seat and under intake they should should be pulled away from the seat. Obviously I am missing something. Maybe it is time to do something else for a while. Probably not the Atkinson Differential because that is also just a source of frustration.

 

[scottyp]

Is one of your valves opening even the slightest amount? How tight are your pushrods/rockers? Maybe test the compression with the pushrods removed. Or is the valve timing off?

 

[Gordon]

I put in stronger spring and actually tried it with the push rods removed. It is strange that both cylinders seem to have the same good intake suction and poor compression pressure. If it was a valve it not seem to be the same in both cylinders. Also the valves do not seem to be leaking under 20 PSI from the compressor.

 

[Richard Hed]

I put in stronger spring and actually tried it with the push rods removed. It is strange that both cylinders seem to have the same good intake suction and poor compression pressure. If it was a valve it not seem to be the same in both cylinders. Also the valves do not seem to be leaking under 20 PSI from the compressor.

Could you show some photos? Have you examined the edges of the rings for bevels or mayb e tiny holes on ONE edge. Doesn't sound like it but there might be some systematic error that you have unknowingly introduced (I mean, obviously it is that, but what?) I am very curious about this. Sounds like timing. Can you send a photo of the valves and their seating?

How about testing the compression with an O-ring?

 

[goldstar31]

'Richard', in full size practice a compression tester is 'cheap as chips' and I saw one for under £10 sterling. It was intended to be screwed into the sparking plug holes and rev'ed up to record the pressure in each cylinder. If one record in a cylinder is low, it is logical to determine the cause.
It way be a broken rin, or one of the valves is not seating properly. To determine the possible valve leak each combustion chamber is filled with kerosene and perhaps a dash of oil.- and left. If the inlet is oiled, that is the one to tackle-- etc etc. There should be no difficulty in making am adapt the gauge to suit smaller plugs
When altering and balancing combustion chambers, the oil/kerosene method was again employed but a clear cover with a hole was used to measure the contents using a burette.
OK, this is NOT an exhaustive reply on how to - say, do up a cylinder head but it gives the principles which are normally employed.
I look forward to reading how successful my recommendations have been.
Regards

Norman

 

[dsage]

Gordon:
Somewhat as suggested by Norman.
Remove the head and turn it upside down with the spark plug in the hole. Use some thin slovent like brake clean, kerosene or varsol and fill the head pocket. It should remain there indefinatley . If you have any leaking then your valves are defective. Even with light spring pressure they should seal. If not re-lap them.
Applying 20lbs of cylnder air pressure will be helping them seal. You need a good seal with no cylinder pressure and just the spring pressure.
I can't explain your observation of the valves sealing better under suction. You could also have cylinder leakage. This test will at least rule out the valves. Then you can concentrate on the pistons / rings later.

 

[Gordon]

Gordon:
Somewhat as suggested by Norman.
Remove the head and turn it upside down with the spark plug in the hole. Use some thin slovent like brake clean, kerosene or varsol and fill the head pocket. It should remain there indefinatley . If you have any leaking then your valves are defective. Even with light spring pressure they should seal. If not re-lap them.
Applying 20lbs of cylnder air pressure will be helping them seal. You need a good seal with no cylinder pressure and just the spring pressure.
I can't explain your observation of the valves sealing better under suction. You could also have cylinder leakage. This test will at least rule out the valves. Then you can concentrate on the pistons / rings later.

The head is completely flat so I cannot fill a cavity to test the valves unless I machine a false cavity ring. The thing that has me the most confused is why the rings seem to seal better in one direction than the other. This is true even when I remove the head and seal the cylinder with my hand over the opening.

Norman: What tester are you recommending? Everything I have tried just bounces around at every stroke and does not tell me anything.

 

[goldstar31]

Norman: What tester are you recommending? Everything I have tried just bounces around at every stroke and does not tell me anything.

When I was 'Doing' cylinder heads, I used standard cheap pressure tester which had a ribber 'bung' and a non return valve which, as the revs continued the pressure contued to go up- and the stopped. Like a compressor dial? For the next cylinder, the valve( like a tire valve, was let down with a finger nail and another test was take and so on,
I'm sure that you will see this at any garage. Drive into any one and ask the guy to pull your plugs and with the starter cranking your engine will take readings for each cylinder.

 

[tornitore45]

Valve leakage under intake vacuum (1 atmosphere) is much less than valve leakage under "Compression Ratio" like 7 atmospheres. Hence the suction seems better than the compression.
Forget the difference, leakage is leakage and is either through the valves, the rings or the head (gasket or not).

Valve seating has been discussed to death. The main idea is keep the seating ring thin, some people use slightly different angles on valve and seat to force a thin rim. Start with a shiny valve and seat, as you grind the surfaces the abrasive turns them dull gray. When you see an interrupted, thin gray ring area all around the seat and the valve you are done.

After some running under power you can see an axial pattern wear on the rings. If some area shows the rubbing pattern an some area is still shiny you know the shiny part is not in contact with the sleeve.

The head mating surfaces need to be true to each other, Flat, polished and square. Start with hand tightening the 4 screws diagonally and then tighten them progressively a bit at the time to assure even seating. If the head goes on cocked it leaks.

I built the same engine, and had fits to run because without the plug booths the spark jumped to one of the push rods. With the booths it run fine.

 

[Gordon]

When I was 'Doing' cylinder heads, I used standard cheap pressure tester which had a ribber 'bung' and a non return valve which, as the revs continued the pressure contued to go up- and the stopped. Like a compressor dial? For the next cylinder, the valve( like a tire valve, was let down with a finger nail and another test was take and so on,
I'm sure that you will see this at any garage. Drive into any one and ask the guy to pull your plugs and with the starter cranking your engine will take readings for each cylinder.

I have one of those but the volume in these small engines is not enough to actually register. The air in the cylinder just inflates the coil in the gage.

 

[goldstar31]

The head is completely flat so I cannot fill a cavity to test the valves unless I machine a false cavity ring. The thing that has me the most confused is why the rings seem to seal better in one direction than the other. This is true even when I remove the head and seal the cylinder with my hand over the opening.

Eh? Pardon?

Remove the head with the plugs in and turn it with the head so that is flat and measure the cavity with oil mixture and then check for the valve which is leaking( or not)
Checking a valve seating is use a thin rim of grinding paste and create a thin continuous 'ring' of ground metal.
If things are worse than that, you have to do any number of things like recutting vaves and possibly guides but I must again confirm that this is standard practice

 

[Gordon]

Valve leakage under intake vacuum (1 atmosphere) is much less than valve leakage under "Compression Ratio" like 7 atmospheres. Hence the suction seems better than the compression.
Forget the difference, leakage is leakage and is either through the valves, the rings or the head (gasket or not).

Valve seating has been discussed to death. The main idea is keep the seating ring thin, some people use slightly different angles on valve and seat to force a thin rim. Start with a shiny valve and seat, as you grind the surfaces the abrasive turns them dull gray. When you see an interrupted, thin gray ring area all around the seat and the valve you are done.

After some running under power you can see an axial pattern wear on the rings. If some area shows the rubbing pattern an some area is still shiny you know the shiny part is not in contact with the sleeve.

The head mating surfaces need to be true to each other, Flat, polished and square. Start with hand tightening the 4 screws diagonally and then tighten them progressively a bit at the time to assure even seating. If the head goes on cocked it leaks.

I built the same engine, and had fits to run because without the plug booths the spark jumped to one of the push rods. With the booths it run fine.

My next step is extended runnin under power. I made a sheave to fit on the crankshaft so that I can hook it to an electric motor. I wall also try lapping the valves again.

 

[Gordon]

Eh? Pardon?

Remove the head with the plugs in and turn it with the head so that is flat and measure the cavity with oil mixture and then check for the valve which is leaking( or not)
Checking a valve seating is use a thin rim of grinding paste and create a thin continuous 'ring' of ground metal.
If things are worse than that, you have to do any number of things like recutting vaves and possibly guides but I must again confirm that this is standard practice

There is no cavity to fill. The head is flat. I have done the valve lap steps but it certainly will not hurt to try again. Sometimes we are too easily satisfied and move on before we are 100% sure. At least I do.

 

[goldstar31]

I have one of those but the volume in these small engines is not enough to actually register. The air in the cylinder just inflates the coil in the gage.

Having seen tests done on Aqualung bottles, you can change from air to oil. Oil does not compress

 

[dsage]

Flat head - then still easy to check.
Fill the intake / exhaust port(s) with the liquid. Either way the valve should stop the fluid and it should stay there.

Just my opinion but I don't think running it to death under external power is the answer. Analyze the problems and try to solve them. Excessive running is just as likely to wear it out as wear it in.

(I say that as I ponder why my Atkinson engine has the same issues and I've made no progress. Of course it has no heads so......)

I agree with your sentiment:
>> Sometimes we are too easily satisfied and move on before we are 100% sure. At least I do.

 

[goldstar31]

[

(I say as I ponder why my Atkinson engine has the same issues and I've made no progress)
[/QUOTE]
s so......)
[/QUOTE]
Of course if your surname is Atkinson


Norman Atkinson

 

[dsage]

Ahhh. So it's all your fault Norman

 

[goldstar31]

there's many a true word spoken in jest.

Granddad Sam worked for Timothy Hackworth and the three boys were all into engines being blacksmiths. Me, nah, never wanted dirty hands- a tuned a few cars. More like the other nut case who was kicked out of every school and he became an engineering graduate and then thought better of it and became BlackAdder and Mr Bean. Actually he was a racing driver .
Me I'm the dreamy one, no education, no nothing, never had a job for the last 35 years.
Just a confused alcoholic who has set off to save the world by re-cycling as many empty bottles as possible.
Hic

Norm

 

[johwen]

If you have uneven compression in Cylinders it is a good idea to check the deck height of the piston at TDC as this can vary the compression pressure.
In small engines this is quite critical in achieving equal performance from each cylinder as a few thou can sow quite significantly. This is assuming your valves an piston rings are seating correctly. When checking valve seating on these small engines I user a magnifying glass to look at the lapped surfaces to see if they are even for the full circle of the valve and seat. Cheers. Johwen.

 

[goldstar31]

What seems to be another World but I was an avid reader of a British Magazine called 'Cars and Car Conversions' which led me to David Vizard's books on Tuning A Series engines which, of course, included the BMC Mini series.