new leakdown results

comnoz · Dec 30, 2014

Here is ny new leakdown test results now that then engine has been run long enough to seat the new rings.
Disappointing.

[video]http://youtu.be/56MUkpAFffg[/video]

Hobot · Dec 30, 2014

Ugh guess you've wasted enough down time on home DIY attempts by now so may want to send it to a pro soon

What pressure are you testing with as seems too easy to hold with one hand on breaker bar.

Torontonian · Dec 30, 2014

Valves.

comnoz · Dec 30, 2014

hobot said:
Ugh guess you've wasted enough down time on home DIY attempts by now so may want to send it to a pro soon
What pressure are you testing with as seems too easy to hold with one hand on breaker bar.

There is a pressure regulator in the tester. You adjust it to zero the gauge. It's in the 50 lb area.

comnoz · Dec 30, 2014

Torontonian said:
Valves.

Zero leakage past the valves. I use a stethoscope to listen to the intake and exhaust.

If you listen in the video you can hear the reed valve singing as the air escapes the crankcase.

Torontonian · Dec 30, 2014

O.K. I usually suspect valve seatings first.

rx7171 · Dec 31, 2014

comnoz said:
Here is ny new leakdown test results now that then engine has been run long enough to seat the new rings.
Disappointing.

[video]http://youtu.be/56MUkpAFffg[/video]

I assume you are very careful with your piston to cylinder wall gap.
So are the pistons very short skirted to make the rocking more sustantial?
If so how do you avoid this with short skirt pistons other than tighter cylinder wall gap than recommended.

comnoz · Dec 31, 2014

rx7171 said:
I assume you are very careful with your piston to cylinder wall gap.
So are the pistons very short skirted to make the rocking more sustantial?
If so how do you avoid this with short skirt pistons other than tighter cylinder wall gap than recommended.

They are a semi short piston with a high wrist pin position.

I have two choices.

1. less piston to wall clearance -which can't be done with forged pistons in an air cooled iron bore.

2. A lower pin position in the piston along with a longer skirt -which means either a shorter rod or a taller barrel.

But as it is now the only problems I am having are a little higher oil consumption and a few drops of oil being blown from the oil tank vent tube. I guess I will live with it till the new motor is finished. Jim

Hobot · Dec 31, 2014

Sheeze Jim, just knurl the loose forged pistons and let them wear to happest non slap slack while seating new rings and redo your dyno to see if the oil layer trapping helps the rwhp as rpm climbs. Should last as long as takes a new engine brewed up.

comnoz · Dec 31, 2014

hobot said:
Sheeze Jim, just knurl the loose forged pistons and let them wear to happest non slap slack while seating new rings and redo your dyno to see if the oil layer trapping helps the rwhp as rpm climbs. Should last as long as takes a new engine brewed up.

What good would that do. Even if they didn't seize they would still wear back to the minimum amount of clearance -which is about .006.

Hobot · Dec 31, 2014

I don't really know but Peel's loose knurled pistons seemed to lower redline friction significantly. Otherwise only opition pretty much like the rest of us, more offerings on the shelf sacrificed for the need for speed. If I ever get Peel running to ride to your shop would be very interesting to examine her piston scuff marks to guide a 2nd dyno with surface texture and relieving done guided by the research article that found decreased bore friction. Ken sent Peel engine mounted horizontal so looks like obsolete hit/miss antique it is, w/o some helpers.

worntorn · Dec 31, 2014

comnoz said:
What good would that do. Even if they didn't seize they would still wear back to the minimum amount of clearance -which is about .006.

Hmmmm
I'm running forged CP Carillo 92 mm pistons in a cast iron liner/aluminium muff at. 0035" skirt clearance. This is the clearance called for in the instructions that came with the components for the 1360 Vincent top end, clearance specs by CP Carillo.
Only a few hundred miles on it so far, so I will not claim success, but the clearance number is pretty tight compared with your 6 thou on an 81? mm bore.
I guess time will tell if the three and a half is adequate.
These are also Shorty pistons. The leakdown test was excellent, but I did not try the second part as shown in your video , going over tdc . Will try that and see if the number changes.

Glen

Hobot · Dec 31, 2014

Glen be pensive as Ken Canaga race tested clearance in 920's w your type cylinders. He renewed failed engine from .035" piston manufacturer listed by .0005" each time till he found .0055" as minimum. Might want to peek in at piston scuff to get a sense of your seize reserves ahead of time. Good thing comnoz reed breather plumbing can keep up with his blow by.

I don't know how to tell ahead of time so would like to be filled in how to.

comnoz · Dec 31, 2014

worntorn said:
comnoz said:

What good would that do. Even if they didn't seize they would still wear back to the minimum amount of clearance -which is about .006.

Click to expand...

Hmmmm
I'm running forged CP Carillo 92 mm pistons in a cast iron liner/aluminium muff at. 0035" skirt clearance. This is the clearance called for in the instructions that came with the components for the 1360 Vincent top end, clearance specs by CP Carillo.
Only a few hundred miles on it so far, so I will not claim success, but the clearance number is pretty tight compared with your 6 thou on an 81? mm bore.
I guess time will tell if the three and a half is adequate.
These are also Shorty pistons. The leakdown test was excellent, but I did not try the second part as shown in your video , going over tdc . Will try that and see if the number changes.

Glen

I would bet that with .0035 clearance you will be OK. The aluminum muff helps. If the liners are austentic cast iron then that helps even more.

I wish I could get away being that tight on the Norton but experience has shown that seizure will be almost immediate at .005 and you have to be really careful to get by at .0055 with JE pistons in a Norton iron barrel.

When I bored mine I set the clearance at .0058. That grew to .0065 in the first 9000 miles. All bore wear and no measurable piston wear. I am using high strength sleeves.

Leakage problems usually show up first ATDC. Jim

WZ507 · Dec 31, 2014

worntorn said:
comnoz said:

What good would that do. Even if they didn't seize they would still wear back to the minimum amount of clearance -which is about .006.

Click to expand...

Hmmmm
I'm running forged CP Carillo 92 mm pistons in a cast iron liner/aluminium muff at. 0035" skirt clearance. This is the clearance called for in the instructions that came with the components for the 1360 Vincent top end, clearance specs by CP Carillo.
Only a few hundred miles on it so far, so I will not claim success, but the clearance number is pretty tight compared with your 6 thou on an 81? mm bore.
I guess time will tell if the three and a half is adequate.
These are also Shorty pistons. The leakdown test was excellent, but I did not try the second part as shown in your video , going over tdc . Will try that and see if the number changes.

Glen

I think there is a night and day difference between a cast iron cylinder with cast iron sleeve and a cast iron sleeve in an aluminum cylinder. Differences in the piston design/shape/taper also have to be factored into any sizing comparison.

This subject of leak down testing was well hashed over here recently with the conclusion that there was not one standard differential compression test, thus results were difficult to compare between various testers using various gauges and pressures. The closest we came to a standard test was the FAA specification for a 0.040" dia orifice between gauges and 80 psi pressure applied to the regulated gauge. See the "Differential Compression Test" description on page 8-7 of the following document.

http://rgl.faa.gov/Regulatory_and_Guida ... r%2008.pdf

Racing engine builders trying to cut a finer performance line are known to reduce the orifice to 0.020" dia to make the test even more discriminating.

That’s said, please tell us more about your leak down test and results, e.g., what orifice dia does your leak down rig employ, what was the regulated test pressure, and what % leakage did you record? Thank you.

comnoz · Dec 31, 2014

WZ507 said:
I think there is a night and day difference between a cast iron cylinder with cast iron sleeve and a cast iron sleeve in an aluminum cylinder. Differences in the piston design/shape/taper also have to be factored into any sizing comparison.

This subject of leak down testing was well hashed over here recently with the conclusion that there was not one standard differential compression test, thus results were difficult to compare between various testers using various gauges and pressures. The closest we came to a standard test was the FAA specification for a 0.040" dia orifice between gauges and 80 psi pressure applied to the regulated gauge. See the "Differential Compression Test" description on page 8-7 of the following document.

http://rgl.faa.gov/Regulatory_and_Guida ... r%2008.pdf

Racing engine builders trying to cut a finer performance line are known to reduce the orifice to 0.020" dia to make the test even more discriminating.

That’s said, please tell us more about your leak down test and results, e.g., what orifice dia does your leak down rig employ, what was the regulated test pressure, and what % leakage did you record? Thank you.

I do not know what size orifice is in my leakdown tester. I had told you it was a Snap-on tester but realized later it is a Sun tester or 70's vintage. I would need to tear it apart to measure the orifice but I will check the pressure.

I do not attempt to compare reading with other testers. I only use it to compare readings over time or for diagnostics.

I do know that a really nice motor with conventional rings will give about 6% on both sides of TDC on my tester.
About 4% is the best I have seen with Total Seal rings.

I recorded 8% BTDC and 20% ATDC. It is only a couple percent less than it was before I installed new rings but it is a little more consistent. I generally tend to quote an average [14%] although I think the leakdown after TDC is the more important figure.
Jim

Snotzo · Jan 1, 2015

Jim
your concern should be confined to determining the reason for the high leakage past the rings, not the diameter of orifice in your tester!
You mention both 'conventional' rings and Total Seal rings. Is it not possible to fit a set of either and then make a direct comparison with previous results ?
It is also worth bearing in mind that your test is one performed on a static engine, and as such it may bear no comparison to the situation in the same engine when running. Ring pressures in a static engine need only be sufficient to effect a seal that will enable the engine to be started. Thereafter combustion pressures acting behind the ring will create much higher sealing pressures, way beyond what are possible with conventional static test equipment.
It may well be that when running your engine the rings are sealing well, but to make any meaningful measurements to determine just how well they seal is very different matter from simple static engine tests

gjr · Jan 1, 2015

comnoz said:
When I bored mine I set the clearance at .0058. That grew to .0065 in the first 9000 miles. All bore wear and no measurable piston wear. I am using high strength sleeves.
Jim

Hi Jim,

Interesting stuff.
How many miles on the engine now ?
What are you seeing for oil consumption ?
At 9000 miles did you see any ring wear ?

Thanks

Greg

comnoz · Jan 1, 2015

gjr said:
comnoz said:

When I bored mine I set the clearance at .0058. That grew to .0065 in the first 9000 miles. All bore wear and no measurable piston wear. I am using high strength sleeves.
Jim

Click to expand...

Hi Jim,

Interesting stuff.
How many miles on the engine now ?
What are you seeing for oil consumption ?
At 9000 miles did you see any ring wear ?

Thanks

Greg

The engine has a little over 9000 miles since it was built.

The ring gap had increased quite a bit during that 9000 miles. I was hoping new rings with a tight end gap might reduce the leakdown and oil consumption.

I used a couple quarts returning from Barbers. So I figure 5 to 700 miles per quart.

What bothers me the most is the fact that the blowby is high enough to blow oil out of the oil tank breather. That had never happened with the old motor -even with 85,000 miles on it.

The last leakdown figures I have recorded on my old motor was 13 and 14 percent. They had been about the same before and after TDC. That was at 70,000 miles.

I won't be installing Total Seal rings. It is tough enough to kick through now. Jim

Hobot · Jan 1, 2015

What bothers me the most is the fact that the blowby is high enough to blow oil out of the oil tank breather. That had never happened with the old motor -even with 85,000 miles on it.

This could be a real learning saga for all of us as its the exceptions to the rules that reveal deeper factors over looked prior. Only got so much life time left to get on with the show so hope you figure it out for us.

new leakdown results

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