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Your temperatures don't sound all that bad for breaking in cylinders, but you should go back over the baffling. The baffling is there to maintain pressure in the plenum with the help of those rubber strip seals, and to force air at high velocity between the cylinder fins as it makes its way through to the low pressure side. The baffling has to be right against the fins so air can't go around the fins. Baffles that don't fit properly prevents the air from picking up enough heat from the fins and even if you have normal temps you can have hot spots.

Yes cylinders will run hot as the piston rings wear off the ridges of the honed surface of the cylinder wall. On the other hand, I wouldn't be surprised at all to see high cylinder temps after 20 minutes of ground running on any tightly cowled pusher where the airflow is only from a gentle suction on the exhaust side from the prop. If you're at idle and the wind is behind you opposing what little cooling flow there is, typical when sitting in a line up on a taxi way, the engine is getting very little cooling flow at all so naturally you have an Easy Bake Oven running behind you.

In a Long Eze you should avoid long idle periods like that, especially during break-in. Especially out of wind. And in fact, until break-in is complete (oil consumption will stabilize and CHTs will drop) you should avoid flying in circumstances where you have to sit in line on a taxiway without shutting down (At Oshkosh I remember watching the Eze drivers shut down, get out and push their planes along as the departure line of aircraft moved along to avoid the 20 minute ground run cooking their engines during the post airshow escape crush).

Another minor point is, if the EGTsCHTs are working off thermocouple washers instead of the screw-in probes of the threaded hole provided for the purpose under the Lycoming cylinder, the CHTs will read higher because the area around the plug where the washer senses gets the heat from the plug, which is always hotter than the surrounding aluminum. Especially if they are washers on the lower plugs (Continentals use the washers, usually on the top plugs - Lycomings have the dedicated temperature probe well underneath, but sometimes you will find the washers used on Lycs if it was a later add on).

Your temperatures don't sound all that bad for breaking in cylinders, but you should go back over the baffling. The baffling is there to maintain pressure in the plenum with the help of those rubber strip seals, and to force air at high velocity between the cylinder fins as it makes its way through to the low pressure side. The baffling has to be right against the fins so air can't go around the fins. Baffles that don't fit properly prevents the air from picking up enough heat from the fins and even if you have normal temps you can have hot spots.

Yes cylinders will run hot as the piston rings wear off the ridges of the honed surface of the cylinder wall. On the other hand, I wouldn't be surprised at all to see high cylinder temps after 20 minutes of ground running on any tightly cowled pusher where the airflow is only from a gentle suction on the exhaust side from the prop. If you're at idle and the wind is behind you opposing what little cooling flow there is, typical when sitting in a line up on a taxi way, the engine is getting very little cooling flow at all so naturally you have an Easy Bake Oven running behind you.

In a Long Eze you should avoid long idle periods like that, especially during break-in. Especially out of wind. And in fact, until break-in is complete (oil consumption will stabilize and CHTs will drop) you should avoid flying in circumstances where you have to sit in line on a taxiway without shutting down (At Oshkosh I remember watching the Eze drivers shut down, get out and push their planes along as the departure line of aircraft moved along to avoid the 20 minute ground run cooking their engines during the post airshow escape crush).

Another minor point is, if the EGTs are working off thermocouple washers instead of the screw-in probes of the threaded hole provided for the purpose under the Lycoming cylinder, the CHTs will read higher because the area around the plug where the washer senses gets the heat from the plug, which is always hotter than the surrounding aluminum. Especially if they are washers on the lower plugs (Continentals use the washers, usually on the top plugs - Lycomings have the dedicated temperature probe well underneath, but sometimes you will find the washers used on Lycs if it was a later add on).

Your temperatures don't sound all that bad for breaking in cylinders, but you should go back over the baffling. The baffling is there to maintain pressure in the plenum with the help of those rubber strip seals, and to force air at high velocity between the cylinder fins as it makes its way through to the low pressure side. The baffling has to be right against the fins so air can't go around the fins. Baffles that don't fit properly prevents the air from picking up enough heat from the fins and even if you have normal temps you can have hot spots.

Yes cylinders will run hot as the piston rings wear off the ridges of the honed surface of the cylinder wall. On the other hand, I wouldn't be surprised at all to see high cylinder temps after 20 minutes of ground running on any tightly cowled pusher where the airflow is only from a gentle suction on the exhaust side from the prop. If you're at idle and the wind is behind you opposing what little cooling flow there is, typical when sitting in a line up on a taxi way, the engine is getting very little cooling flow at all so naturally you have an Easy Bake Oven running behind you.

In a Long Eze you should avoid long idle periods like that, especially during break-in. Especially out of wind. And in fact, until break-in is complete (oil consumption will stabilize and CHTs will drop) you should avoid flying in circumstances where you have to sit in line on a taxiway without shutting down (At Oshkosh I remember watching the Eze drivers shut down, get out and push their planes along as the departure line of aircraft moved along to avoid the 20 minute ground run cooking their engines during the post airshow escape crush).

Another minor point is, if the CHTs are working off thermocouple washers instead of the screw-in probes of the threaded hole provided for the purpose under the Lycoming cylinder, the CHTs will read higher because the area around the plug where the washer senses gets the heat from the plug, which is always hotter than the surrounding aluminum. Especially if they are washers on the lower plugs (Continentals use the washers, usually on the top plugs - Lycomings have the dedicated temperature probe well underneath, but sometimes you will find the washers used on Lycs if it was a later add on).

    Post Undeleted by John K
2 Rewritten because I missed the fact that the he said the baffling was already redone.
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The FBO's comment on the cowling hit the nail on the head and is a huge red flag. Cowling baffling condition is a BIG deal, especially on a tightly cowled pusher like the Long Eze.

On airplanes with pressure cowls, with a high pressure plenum on the intake side and a low pressure plenum on the exhaust sideYour temperatures don't sound all that bad for breaking in cylinders, but you should go back over the baffling is critical. The baffling is there to maintain pressure in the plenum with the help of those rubber strip seals, and to force air at high velocity between the cylinder fins as it makes its way through to the low pressure side. The baffling has to be right against the fins so air can't go around the fins. So bad seals allows air to bypass the engine completely, and baffles Baffles that don't fit properly preventprevents the air from picking up enough heat from the fins.

It's made more critical by the fact that a pusher with a tight low drag cowl is way harder to cool on the ground. The pressure differential between the high pressure and low pressure side of cowling plenum is being created by "vacuum" of the prop sucking air which is much less effective than a prop in front "blowing" air into the high pressure side of the plenum, which is designed to function with ram air. You get way less flow andeven if you have to optimize the cowl and baffling as much as possible - leakage and losses tolerable on a tractor engine are no good on a tightly cowled pusher like thatnormal temps you can have hot spots.  

Yes cylinders will run hot as the piston rings wear off the ridges of the honed surface of the cylinder wall. On the other hand, I wouldn't be surprised at all to see high cylinder temps after 20 minutes of ground running on any tightly cowled pusher where the airflow is only from a gentle suction on the exhaust side from the prop. If you're at idle and the wind is behind you opposing what little cooling flow there is, typical when sitting in a line up on a taxi way, the engine is getting very little cooling flow at all so naturally you have an Easy Bake Oven running behind you.

I would say then, that priority #1, to protect your 20 grand overhaul, is repair/rebuild the baffling so it is well sealed and fits tightly to the cylinder fins. This is a must. Even if your cylinder head temps are normal, bad baffling can create hot spots on the cylinders that go undetected by the probe.

In the mean time, if you really want to keep flying it,a Long Eze you should avoid long idle periods like that, especially during break-in. Especially out of wind. And in fact, until break-in is complete (oil consumption will stabilize and CHTs will drop) you should avoid flying in circumstances where you have to sit in line on a taxiway without shutting down (At Oshkosh I remember watching the Eze drivers shut down, get out and push their planes along as the departure line of aircraft moved along to avoid the 20 minute ground run cooking their engines during the post airshow escape crush).

Another minor point is, if the EGTs are working off thermocouple washers instead of the screw-in probes of the threaded hole provided for the purpose under the Lycoming cylinder, the CHTs will read higher because the area around the plug where the washer senses gets the heat from the plug, which is always hotter than the surrounding aluminum. Especially if they are washers on the lower plugs (Continentals use the washers, usually on the top plugs - Lycomings have the dedicated temperature probe well underneath, but sometimes you will find the washers used on Lycs if it was a later add on).

But in any case, two major takeaways: Avoid long ground runs in airplanes like the Long Eze to the extent you can, and fix the baffling.

The FBO's comment on the cowling hit the nail on the head and is a huge red flag. Cowling baffling condition is a BIG deal, especially on a tightly cowled pusher like the Long Eze.

On airplanes with pressure cowls, with a high pressure plenum on the intake side and a low pressure plenum on the exhaust side, the baffling is critical. The baffling is there to maintain pressure in the plenum with the help of those rubber strip seals, and to force air at high velocity between the cylinder fins as it makes its way through to the low pressure side. The baffling has to be right against the fins so air can't go around the fins. So bad seals allows air to bypass the engine completely, and baffles that don't fit properly prevent the air from picking up enough heat from the fins.

It's made more critical by the fact that a pusher with a tight low drag cowl is way harder to cool on the ground. The pressure differential between the high pressure and low pressure side of cowling plenum is being created by "vacuum" of the prop sucking air which is much less effective than a prop in front "blowing" air into the high pressure side of the plenum, which is designed to function with ram air. You get way less flow and have to optimize the cowl and baffling as much as possible - leakage and losses tolerable on a tractor engine are no good on a tightly cowled pusher like that.  

Yes cylinders will run hot as the piston rings wear off the ridges of the honed surface of the cylinder wall. On the other hand, I wouldn't be surprised at all to see high cylinder temps after 20 minutes of ground running on any tightly cowled pusher. If you're at idle and the wind is behind you opposing what little cooling flow there is, typical when sitting in a line up on a taxi way, the engine is getting very little cooling flow at all so naturally you have an Easy Bake Oven running behind you.

I would say then, that priority #1, to protect your 20 grand overhaul, is repair/rebuild the baffling so it is well sealed and fits tightly to the cylinder fins. This is a must. Even if your cylinder head temps are normal, bad baffling can create hot spots on the cylinders that go undetected by the probe.

In the mean time, if you really want to keep flying it, you should avoid long idle periods like that, especially during break-in. Especially out of wind. And in fact, until break-in is complete (oil consumption will stabilize and CHTs will drop) you should avoid flying in circumstances where you have to sit in line on a taxiway without shutting down (At Oshkosh I remember watching the Eze drivers shut down, get out and push their planes along as the departure line of aircraft moved along to avoid the 20 minute ground run cooking their engines during the post airshow escape crush).

Another minor point is, if the EGTs are working off thermocouple washers instead of the screw-in probes of the threaded hole provided for the purpose under the Lycoming cylinder, the CHTs will read higher because the area around the plug where the washer senses gets the heat from the plug, which is always hotter than the surrounding aluminum. Especially if they are washers on the lower plugs (Continentals use the washers, usually on the top plugs - Lycomings have the dedicated temperature probe well underneath, but sometimes you will find the washers used on Lycs if it was a later add on).

But in any case, two major takeaways: Avoid long ground runs in airplanes like the Long Eze to the extent you can, and fix the baffling.

Your temperatures don't sound all that bad for breaking in cylinders, but you should go back over the baffling. The baffling is there to maintain pressure in the plenum with the help of those rubber strip seals, and to force air at high velocity between the cylinder fins as it makes its way through to the low pressure side. The baffling has to be right against the fins so air can't go around the fins. Baffles that don't fit properly prevents the air from picking up enough heat from the fins and even if you have normal temps you can have hot spots.

Yes cylinders will run hot as the piston rings wear off the ridges of the honed surface of the cylinder wall. On the other hand, I wouldn't be surprised at all to see high cylinder temps after 20 minutes of ground running on any tightly cowled pusher where the airflow is only from a gentle suction on the exhaust side from the prop. If you're at idle and the wind is behind you opposing what little cooling flow there is, typical when sitting in a line up on a taxi way, the engine is getting very little cooling flow at all so naturally you have an Easy Bake Oven running behind you.

In a Long Eze you should avoid long idle periods like that, especially during break-in. Especially out of wind. And in fact, until break-in is complete (oil consumption will stabilize and CHTs will drop) you should avoid flying in circumstances where you have to sit in line on a taxiway without shutting down (At Oshkosh I remember watching the Eze drivers shut down, get out and push their planes along as the departure line of aircraft moved along to avoid the 20 minute ground run cooking their engines during the post airshow escape crush).

Another minor point is, if the EGTs are working off thermocouple washers instead of the screw-in probes of the threaded hole provided for the purpose under the Lycoming cylinder, the CHTs will read higher because the area around the plug where the washer senses gets the heat from the plug, which is always hotter than the surrounding aluminum. Especially if they are washers on the lower plugs (Continentals use the washers, usually on the top plugs - Lycomings have the dedicated temperature probe well underneath, but sometimes you will find the washers used on Lycs if it was a later add on).

    Post Deleted by John K
1
source | link

The FBO's comment on the cowling hit the nail on the head and is a huge red flag. Cowling baffling condition is a BIG deal, especially on a tightly cowled pusher like the Long Eze.

On airplanes with pressure cowls, with a high pressure plenum on the intake side and a low pressure plenum on the exhaust side, the baffling is critical. The baffling is there to maintain pressure in the plenum with the help of those rubber strip seals, and to force air at high velocity between the cylinder fins as it makes its way through to the low pressure side. The baffling has to be right against the fins so air can't go around the fins. So bad seals allows air to bypass the engine completely, and baffles that don't fit properly prevent the air from picking up enough heat from the fins.

It's made more critical by the fact that a pusher with a tight low drag cowl is way harder to cool on the ground. The pressure differential between the high pressure and low pressure side of cowling plenum is being created by "vacuum" of the prop sucking air which is much less effective than a prop in front "blowing" air into the high pressure side of the plenum, which is designed to function with ram air. You get way less flow and have to optimize the cowl and baffling as much as possible - leakage and losses tolerable on a tractor engine are no good on a tightly cowled pusher like that.

Yes cylinders will run hot as the piston rings wear off the ridges of the honed surface of the cylinder wall. On the other hand, I wouldn't be surprised at all to see high cylinder temps after 20 minutes of ground running on any tightly cowled pusher. If you're at idle and the wind is behind you opposing what little cooling flow there is, typical when sitting in a line up on a taxi way, the engine is getting very little cooling flow at all so naturally you have an Easy Bake Oven running behind you.

I would say then, that priority #1, to protect your 20 grand overhaul, is repair/rebuild the baffling so it is well sealed and fits tightly to the cylinder fins. This is a must. Even if your cylinder head temps are normal, bad baffling can create hot spots on the cylinders that go undetected by the probe.

In the mean time, if you really want to keep flying it, you should avoid long idle periods like that, especially during break-in. Especially out of wind. And in fact, until break-in is complete (oil consumption will stabilize and CHTs will drop) you should avoid flying in circumstances where you have to sit in line on a taxiway without shutting down (At Oshkosh I remember watching the Eze drivers shut down, get out and push their planes along as the departure line of aircraft moved along to avoid the 20 minute ground run cooking their engines during the post airshow escape crush).

Another minor point is, if the EGTs are working off thermocouple washers instead of the screw-in probes of the threaded hole provided for the purpose under the Lycoming cylinder, the CHTs will read higher because the area around the plug where the washer senses gets the heat from the plug, which is always hotter than the surrounding aluminum. Especially if they are washers on the lower plugs (Continentals use the washers, usually on the top plugs - Lycomings have the dedicated temperature probe well underneath, but sometimes you will find the washers used on Lycs if it was a later add on).

But in any case, two major takeaways: Avoid long ground runs in airplanes like the Long Eze to the extent you can, and fix the baffling.