Author Topic: Cylinder leak down testing.  (Read 1039 times)

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Offline Sunny Jim

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Cylinder leak down testing.
« on: October 16, 2020, 05:36:56 AM »
I recently carried out leak down tests on the 124 at approx 900 Miles.
Front cyl - 6% Down
Rear cyl - 8% Down.
Test was done on a warm engine.
I have external breathers but am getting the smallest amount of oil in my intake.
Comp test cold was 252psi front
And 247 psi rear
Daimo rest repeated when hot. Both cylinders were down a little from the cold test, but much closer.
I would appreciate your thoughts.

Offline les

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Re: Cylinder leak down testing.
« Reply #1 on: October 18, 2020, 07:32:31 AM »
8% does not seem all that healthy.  I've got an M8 131" on the bench that's never even been broke in yet and it's getting 97% both front and rear.  I would expect to see an engine with 900 miles to have up around 98%+.

Can you tell if the leak is in the valves or the rings?  If in the rings, then it appears that they have not seated in properly.

Offline PoorUB

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Re: Cylinder leak down testing.
« Reply #2 on: October 18, 2020, 07:55:45 AM »
How have you been riding it?

It maybe too late, but I would go ride the hell out of it before I tore it down. Accelerate hard through a couple gears, and do it several times. Work it hard for a couple rides and try a leak down again.
I am an adult?? When did that happen, and how do I make it stop?!

Offline Sunny Jim

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Re: Cylinder leak down testing.
« Reply #3 on: October 20, 2020, 09:37:55 PM »
If in doubt, Check it out.
Stripped it to find worn valve guides worn fthis had previously sumped badly and a look of oil to the top end) . New heads from a take off!
Cylinders glazed and oil stained.
Hone and new rings. All
Measurements are
Fine!

Offline Sunny Jim

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Re: Cylinder leak down testing.
« Reply #4 on: October 21, 2020, 04:51:49 AM »
If in doubt, Check it out.
Stripped it to find worn valve guides worn fthis had previously sumped badly and a look of oil to the top end) . New heads from a take off!
Cylinders glazed and oil stained.
Hone and new rings. All
Measurements are
Fine!
Sorry for the typos!
All in all it will go back together with a minimum of fuss.
I forgot to mention the rear cylinder ring gaps were all aligned.

Offline kd

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Re: Cylinder leak down testing.
« Reply #5 on: October 21, 2020, 06:59:15 AM »
Deja-vu here.  The same thing happened with my 120 on the dyno during the initial tuning. Have you measured your barrels for out of round.  I would be interested in your results if you did and whether or not the alignment was at a tight or loose side of the barrel.  My barrels were near perfect but there was a marginally detectable out of round (when not in torque plates).  The alignment took place perfectly at the loose spot.

This thread may be of interest. The last post has a pair of links with my specs and a pic of the ring alignment.

https://harleytechtalk.com/htt/index.php/topic,102736.msg1212575.html#msg1212575

FWIW a ball hone and new rings seemed to resolve the problem.  It was almost as though the OEM 4.060 cross hatch angle was too shallow and the rings stalled at that spot. The problem was my crosshatch angle measuring tool was 9 hrs away so that wasn't checked before redoing the cylinder finish.

Added later:

I recognize this example is a twin cam but the M8 is just another form of an air pump with similar barrel requirements.
« Last Edit: October 21, 2020, 08:06:20 AM by kd »
KD

Offline No Cents

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Re: Cylinder leak down testing.
« Reply #6 on: October 22, 2020, 04:30:05 AM »
   check the inside bottom of your cylinders and look to see if you have a line/crack going all the way around the bottom of the cylinders spigots about an inch up from the bottom. I just seen this on both cylinders of a 124 bolt on kit that was tore down.


   added later:
it's just something I would check for beings you have the cylinders off right now.
« Last Edit: October 22, 2020, 05:52:58 AM by No Cents »
08 FLHX my grocery getter, 124ci, wfolarry 110" heads, Burns pipe, 158/152 sae

Offline Sunny Jim

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Re: Cylinder leak down testing.
« Reply #7 on: October 22, 2020, 06:36:49 AM »
   check the inside bottom of your cylinders and look to see if you have a line/crack going all the way around the bottom of the cylinders spigots about an inch up from the bottom. I just seen this on both cylinders of a 124 bolt on kit that was tore down.


   added later:
it's just something I would check for beings you have the cylinders off right
now

👍

Offline Mogollon

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Re: Cylinder leak down testing.
« Reply #8 on: October 24, 2020, 09:52:38 AM »
I recently carried out leak down tests on the 124 at approx 900 Miles.
Front cyl - 6% Down
Rear cyl - 8% Down.
Test was done on a warm engine.
I have external breathers but am getting the smallest amount of oil in my intake.
Comp test cold was 252psi front
And 247 psi rear
Daimo rest repeated when hot. Both cylinders were down a little from the cold test, but much closer.
I would appreciate your thoughts.

There’s lots of red flags, and more going on here than meets the eye. The engine’s showing extreme carbon buildup for only 900 miles. I wouldn’t just slap this engine together. Instead, I’d be thinking more about engine building 101 and blueprinting the top end. Your problems may be caused primarily by poor cylinder bore/ring seal, which can lead to oil sumping, but they may be more widespread.

I’m not sure whose big-bore cylinders you are running, but the moco’s M8 SE kit cylinders are infamous for taper, out-of-round, poor crosshatch pattern, and incorrect piston clearances, leading to blow-by, high oil consumption, and engine oil sumping problems. And cracked bottom cylinder spigots are occasionally found on big-bore cylinders with thin spigot walls. I would check the spigots for both vertical and horizontal cracks. And while you’re at it, check the piston skirts, piston bosses and piston pins for problems.

Here’s a test: place a dial bore gauge into the bottom of a thin cylinder spigot and press hard on the outside of the spigot with your thumb. Check to see if the bore gauge needle moves. I’ll bet at BDC, the piston is placing lots more pressure on the spigot than your thumb is.

The cylinders need a quality bore and hone job. Install a quality set of piston rings (not the cheapies), properly gap the rings, make sure they are not installed upside down, and set the piston deck height to zero.

I’m curious, what pistons are installed, Mahle, CP, Wiseco, J&E?

Make sure your S&S or moco oil pump includes the latest O-ring design. On a street engine, I would just run the latest M8 factory oil pump (circa May 22, 2019-up). You can get one for roughly $130 USD, but it won’t be as pretty as the high-dollar anodized one’s are.

Check the piston oilers for tightness and gasket leaking. Use Cometic piston oiler gaskets and make sure the oiler fastening screws are not bottoming out, reducing clamping force.

Check the connecting rods for tightness. Oil sumping has a tendency for ruining rod-bearing clearances. In my opinion, moco rods are set up way-too tight right from the factory. If the rod bearings are ruined, you can either replace the crank with a new moco SE crank (cheapest), rebuild your stock crank (about same cost as new SE crank, but better), or replace it with a recently announced S&S crank (most costly). If replacing the crank, I would choose a 4.5” stroke, making a 128 ci engine, but you’ll need new pistons with a shorter compression height.

There’s lots of oily carbon on the piston dome and chamber. I would do a basic performance valve job on the heads. You already mentioned that the valve guides are shot. I wonder how that happened so soon. Decarbonize the heads, combustion chambers, ports, etc., perform a professional 5-angle valve and seat reface, then “verify” the combustion chamber cc’s and “again” mathematically calculate the static compression ratio (measure twice, cut once). Finally, install new quality aftermarket valve stem oil seals. You might also want to check the valves spring pressures. I assume you are running stock M8 valves springs with the bolt-in cam. Keep in mind that you are building an air pump, sealed by the rings/bore on the bottom and the valves on the top. To make HP you need heat, and to make heat, you need an excellent sealing pump.

There’s several possible causes for ring gap alignment, but one that is often overlooked is detonation. Your ring gaps were aligned on the rear cylinder, which typically runs hotter than the front cylinder, making it more susceptible to detonation.

In America, your stated cranking compression seems high for running on 91-93 octane pump gas (not E85) street engine. You might get away with it on Friday night bike night, but not normal street riding. Not sure what the pump gas octane rating is Downunder, maybe it’s higher than in America? Running an engine on a cool dyno or even a short ¼-mile drag run is different than running for longer periods on the street, where engine heat sink occurs, easily leading to detonation, especially with a less than perfect tune.

Somewhere you mentioned running 85cc combustion chambers, 11.25:1 static compression ratio, and a CR470 cam, which closes the intake at 40-degrees abdc. I’m not sure what your head gasket thickness is. I would consider getting the static compression down to 10.75:1 to 11:1 for a pump gas street engine with your cam (unless your octane is higher than in America). It’s better to run a compression ratio compatible with the gas octane and more ignition advance, than doing it the inverse way. You’ll make more power this way and have a happier, cooler-running engine. Also, keep in mind that oil in the fuel mixture lowers gasoline octane.

Yeah, I know, I hear street riders bragging about running 12:1 compression on “street pump gas” using a late closing intake valve and retarded timing, and making gobs of power. They may get away with that on E85 or tipping the can, but, realistically, I believe they’re kidding themselves.

Finally, I would do a full dyno tune on the rebuilt engine by a knowledgeable tuner using a TTS or Power Vision tuner, and concentrate not only on the fuel curve but also the EFI ignition advance table for each cylinder. The ignition advance table may need certain areas adjusted independently.

Offline Sunny Jim

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Re: Cylinder leak down testing.
« Reply #9 on: October 24, 2020, 06:20:04 PM »
I recently carried out leak down tests on the 124 at approx 900 Miles.
Front cyl - 6% Down
Rear cyl - 8% Down.
Test was done on a warm engine.
I have external breathers but am getting the smallest amount of oil in my intake.
Comp test cold was 252psi front
And 247 psi rear
Daimo rest repeated when hot. Both cylinders were down a little from the cold test, but much closer.
I would appreciate your thoughts.

There’s lots of red flags, and more going on here than meets the eye. The engine’s showing extreme carbon buildup for only 900 miles. I wouldn’t just slap this engine together. Instead, I’d be thinking more about engine building 101 and blueprinting the top end. Your problems may be caused primarily by poor cylinder bore/ring seal, which can lead to oil sumping, but they may be more widespread.

I’m not sure whose big-bore cylinders you are running, but the moco’s M8 SE kit cylinders are infamous for taper, out-of-round, poor crosshatch pattern, and incorrect piston clearances, leading to blow-by, high oil consumption, and engine oil sumping problems. And cracked bottom cylinder spigots are occasionally found on big-bore cylinders with thin spigot walls. I would check the spigots for both vertical and horizontal cracks. And while you’re at it, check the piston skirts, piston bosses and piston pins for problems.

Here’s a test: place a dial bore gauge into the bottom of a thin cylinder spigot and press hard on the outside of the spigot with your thumb. Check to see if the bore gauge needle moves. I’ll bet at BDC, the piston is placing lots more pressure on the spigot than your thumb is.

The cylinders need a quality bore and hone job. Install a quality set of piston rings (not the cheapies), properly gap the rings, make sure they are not installed upside down, and set the piston deck height to zero.

I’m curious, what pistons are installed, Mahle, CP, Wiseco, J&E?

Make sure your S&S or moco oil pump includes the latest O-ring design. On a street engine, I would just run the latest M8 factory oil pump (circa May 22, 2019-up). You can get one for roughly $130 USD, but it won’t be as pretty as the high-dollar anodized one’s are.

Check the piston oilers for tightness and gasket leaking. Use Cometic piston oiler gaskets and make sure the oiler fastening screws are not bottoming out, reducing clamping force.

Check the connecting rods for tightness. Oil sumping has a tendency for ruining rod-bearing clearances. In my opinion, moco rods are set up way-too tight right from the factory. If the rod bearings are ruined, you can either replace the crank with a new moco SE crank (cheapest), rebuild your stock crank (about same cost as new SE crank, but better), or replace it with a recently announced S&S crank (most costly). If replacing the crank, I would choose a 4.5” stroke, making a 128 ci engine, but you’ll need new pistons with a shorter compression height.

There’s lots of oily carbon on the piston dome and chamber. I would do a basic performance valve job on the heads. You already mentioned that the valve guides are shot. I wonder how that happened so soon. Decarbonize the heads, combustion chambers, ports, etc., perform a professional 5-angle valve and seat reface, then “verify” the combustion chamber cc’s and “again” mathematically calculate the static compression ratio (measure twice, cut once). Finally, install new quality aftermarket valve stem oil seals. You might also want to check the valves spring pressures. I assume you are running stock M8 valves springs with the bolt-in cam. Keep in mind that you are building an air pump, sealed by the rings/bore on the bottom and the valves on the top. To make HP you need heat, and to make heat, you need an excellent sealing pump.

There’s several possible causes for ring gap alignment, but one that is often overlooked is detonation. Your ring gaps were aligned on the rear cylinder, which typically runs hotter than the front cylinder, making it more susceptible to detonation.

In America, your stated cranking compression seems high for running on 91-93 octane pump gas (not E85) street engine. You might get away with it on Friday night bike night, but not normal street riding. Not sure what the pump gas octane rating is Downunder, maybe it’s higher than in America? Running an engine on a cool dyno or even a short ¼-mile drag run is different than running for longer periods on the street, where engine heat sink occurs, easily leading to detonation, especially with a less than perfect tune.

Somewhere you mentioned running 85cc combustion chambers, 11.25:1 static compression ratio, and a CR470 cam, which closes the intake at 40-degrees abdc. I’m not sure what your head gasket thickness is. I would consider getting the static compression down to 10.75:1 to 11:1 for a pump gas street engine with your cam (unless your octane is higher than in America). It’s better to run a compression ratio compatible with the gas octane and more ignition advance, than doing it the inverse way. You’ll make more power this way and have a happier, cooler-running engine. Also, keep in mind that oil in the fuel mixture lowers gasoline octane.

Yeah, I know, I hear street riders bragging about running 12:1 compression on “street pump gas” using a late closing intake valve and retarded timing, and making gobs of power. They may get away with that on E85 or tipping the can, but, realistically, I believe they’re kidding themselves.

Finally, I would do a full dyno tune on the rebuilt engine by a knowledgeable tuner using a TTS or Power Vision tuner, and concentrate not only on the fuel curve but also the EFI ignition advance table for each cylinder. The ignition advance table may need certain areas adjusted independently.

Thanks for your input.
CP pistons with Daytona cylinders.
I have calculated my current specs to run a corrected comp @ 10.5
CCP should hit 228 psi.
The detonation issue is not surprising given the amount of heat measured at the rear cylinder!
I tend to run the bike richer with less timing.
I have data logged several times and generally recorded knock events above 280f . I have had to remove timing on set real occasions.
The valve guide issue (along with worn rocker bushes) is a result of and earlier attempt to go 117 cubes. I hade the heads milled and the cylinder head specialist installed the grub screws SS once recommended. Unfortunately he screwed them to the bottom of the hole, blocking oil flow through the heads. The caused a massive reoccurring problem with sumping and oil starvation in the top of the engine. Oil pressure went through the roof. No fancy oil pumps could cope with it. It was a nightmare but we fixed it( thanks Max) .
Anyway it is going back together now. Ne t winter down under it gets a full rebuild. Cheers! 

Offline HD Street Performance

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Re: Cylinder leak down testing.
« Reply #10 on: October 25, 2020, 07:44:48 AM »
Daytona cylinders IME are very straight and true but unfortunately have a smaller spigot OD so overbores are limited. The S&S come in nice at 4.280.