Rotary Hot Starts
04-14-2014, 01:36 PM
#1
Rotary Hot Starts
Shutting an Rx-8 down and turning it on five seconds later some times takes a little longer, 1.5 sec crank approximately sometimes, where as all other starts are almost instant. Is this typical behavior for a rotary?
I know it's kin o ridiculous to ask, but it's just been bothering me.
Thank you.
I know it's kin o ridiculous to ask, but it's just been bothering me.
Thank you.
04-14-2014, 01:49 PM
#2
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Shutting an Rx-8 down and turning it on five seconds later some times takes a little longer, 1.5 sec crank approximately sometimes, where as all other starts are almost instant. Is this typical behavior for a rotary?
I know it's kin o ridiculous to ask, but it's just been bothering me.
Thank you.
I know it's kin o ridiculous to ask, but it's just been bothering me.
Thank you.
04-14-2014, 02:16 PM
#4
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Harder starts with a hot engine than with a cold engine is one of the hallmark signs of weakening / failed compression. Yours probably isn't dead yet since it doesn't sound that much slower yet, but you may want to get a compression test to confirm or disprove that, so you can start planning ahead if there is a replacement in your future.
04-14-2014, 02:34 PM
#5
Harder starts with a hot engine than with a cold engine is one of the hallmark signs of weakening / failed compression. Yours probably isn't dead yet since it doesn't sound that much slower yet, but you may want to get a compression test to confirm or disprove that, so you can start planning ahead if there is a replacement in your future.
04-14-2014, 02:37 PM
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If everything about the engine, ignition, battery, starter, etc... is in perfect health, the engine will fire just as quickly hot or cold.
The difference is that in a hot engine, the housings expand away from the rotors faster than the rotors expand with them, so there is lower compression when hot naturally. The floating seals can bridge the gap in a healthy engine, but as the seals wear down, that becomes less and less true.
This CAN be opposite, or the same, in piston engines. Forged pistons in a cast iron block tends to be opposite, the pistons expand more than the block, so they are set up to seal good when hot, and have trouble when cold because of the gapping. Formula1 engines are the opposite, more like ours though, in that the engine is actually seized at ambient temp due to tolerances being so close, and it has to be heated up by circulating in hot fluid so things can expand enough to let the engine turn over.
The difference is that in a hot engine, the housings expand away from the rotors faster than the rotors expand with them, so there is lower compression when hot naturally. The floating seals can bridge the gap in a healthy engine, but as the seals wear down, that becomes less and less true.
This CAN be opposite, or the same, in piston engines. Forged pistons in a cast iron block tends to be opposite, the pistons expand more than the block, so they are set up to seal good when hot, and have trouble when cold because of the gapping. Formula1 engines are the opposite, more like ours though, in that the engine is actually seized at ambient temp due to tolerances being so close, and it has to be heated up by circulating in hot fluid so things can expand enough to let the engine turn over.
Last edited by RIWWP; 04-14-2014 at 02:39 PM.
04-14-2014, 02:44 PM
#7
If everything about the engine, ignition, battery, starter, etc... is in perfect health, the engine will fire just as quickly hot or cold.
The difference is that in a hot engine, the housings expand away from the rotors faster than the rotors expand with them, so there is lower compression when hot naturally. The floating seals can bridge the gap in a healthy engine, but as the seals wear down, that becomes less and less true.
This CAN be opposite, or the same, in piston engines. Forged pistons in a cast iron block tends to be opposite, the pistons expand more than the block, so they are set up to seal good when hot, and have trouble when cold because of the gapping. Formula1 engines are the opposite, more like ours though, in that the engine is actually seized at ambient temp due to tolerances being so close, and it has to be heated up by circulating in hot fluid so things can expand enough to let the engine turn over.
The difference is that in a hot engine, the housings expand away from the rotors faster than the rotors expand with them, so there is lower compression when hot naturally. The floating seals can bridge the gap in a healthy engine, but as the seals wear down, that becomes less and less true.
This CAN be opposite, or the same, in piston engines. Forged pistons in a cast iron block tends to be opposite, the pistons expand more than the block, so they are set up to seal good when hot, and have trouble when cold because of the gapping. Formula1 engines are the opposite, more like ours though, in that the engine is actually seized at ambient temp due to tolerances being so close, and it has to be heated up by circulating in hot fluid so things can expand enough to let the engine turn over.
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