Why Apex Seals Fail

[NoDOHC]

Wow! This is awesome information. I have seen the same marking on several sets of housings and I never made the hot plug area connection.

It makes sense that the housings would grow the most next to the spark plug, both because there is a more extended high temperature condition in that region than elsewhere and because the housing is less restrained (threads tend to grow more than smooth holes).

I have known spark plugs to gall in place on rotaries and that the plugs show signs of high combustion temperatures. I have also seen two housings where the apex seal left a large mark in the housing 1/2" to 3/4" after the leading plug hole (looked as if that was where the seal actually failed).

I wonder if a very small bevel around the spark plugs would cause a significant loss of cold compression. This may save apex seals from the spark plug speed bump when under boost.

Fooling with the coolant passages would be difficult, as they go through the intermediate iron and both end plates. Maybe a little porting on #5 (without getting too close to the plug).

Maybe some experienced builders can give a better number on how many housings have this damage.

I can add this as a good reason in the causes of rotary engine failure section once we have more information.

Thanks for the input.

[classicauto]

Originally Posted by NoDOHC

Wow! This is awesome information. I have seen the same marking on several sets of housings and I never made the hot plug area connection.

It makes sense that the housings would grow the most next to the spark plug, both because there is a more extended high temperature condition in that region than elsewhere and because the housing is less restrained (threads tend to grow more than smooth holes).

I have known spark plugs to gall in place on rotaries and that the plugs show signs of high combustion temperatures. I have also seen two housings where the apex seal left a large mark in the housing 1/2" to 3/4" after the leading plug hole (looked as if that was where the seal actually failed).

I wonder if a very small bevel around the spark plugs would cause a significant loss of cold compression. This may save apex seals from the spark plug speed bump when under boost.

Fooling with the coolant passages would be difficult, as they go through the intermediate iron and both end plates. Maybe a little porting on #5 (without getting too close to the plug).

Maybe some experienced builders can give a better number on how many housings have this damage.

I can add this as a good reason in the causes of rotary engine failure section once we have more information.

Thanks for the input.

If you look at used housings, especially high horsepower ones, you will see the carbon buildup at the plugs from the growth. Its a hugely wide spread issue. There's some better discussion on the thread in the other forum....

The main problem is that the temperatures are so out of control in that spot that making headway to reducing them still hasn't brought them down to a level on par with the rest of the housing surface. I've tried all kinds of mods to minimize the growth there but nothing can completely manage it, yet. It only serves to reduce the severity.

I've done a couple different styles of jacket mods, run a high flow (REmedey) waterpump, and use 10 and 10.5 plugs (NGK 7420). Still haven't needed to build my next engine to try the additional web or bridge or heat sink (chunk of AL inserted diagonally in the leading plug cooling passage on both sides of it) out. But I'm not exactly disappointed that I haven't needed another yet

Currently floating around my mind are the idea previously mentioned, as well as running higher system pressure. Much higher. Also, Barry pointed out some NGK surface gap style plugs which appear to perhaps retain less heat given their tip design vs. the 7420's.

[Barry Bordes]

Originally Posted by classicauto

I've done a couple different styles of jacket mods, run a high flow (REmedey) waterpump, and use 10 and 10.5 plugs (NGK 7420). Still haven't needed to build my next engine to try the additional web or bridge or heat sink (chunk of AL inserted diagonally in the leading plug cooling passage on both sides of it) out. But I'm not exactly disappointed that I haven't needed another yet

Currently floating around my mind are the idea previously mentioned, as well as running higher system pressure. Much higher. Also, Barry pointed out some NGK surface gap style plugs which appear to perhaps retain less heat given their tip design vs. the 7420's.

Classicauto, have you measured the gap of the surface gap plugs?

This may be a problem, they may be a little large for boosted engines.

Also it would be nice if they were made of some rare earth metals like platinum or iridium.

Barry