Heat Seize at High Speed? CHT Sensor Leak?
Posted: Mon Dec 12, 2016 8:37 pm
So to start off, I recently did an AF18E ZX swap into a Tact (Aero 50), all components are stock aside from a DD50 intake manifold (w/vacuum port to use with the fuel petcock under the seat), typical transmission parts, Daytona Racing CDI, 8-rated plug, and a CHT sensor/gauge setup. It's winter here and I did a late night run last night. The engine was running well, cruising around 40mph, when the engine starting bogging down. It was still pushing but slowly lost power until coming to a halt on the side of the road. Before it happened, I wasn't constantly holding the throttle wide-open, I started to hold the throttle wide-open when I felt slight power loss and couldn't keep up with traffic, then it slowly died after.
The engine would still idle once stopping on the side of the road, but when I gave it any throttle, the engine would bog and almost stall. Once I let off, the engine would return to idle again. I waited a minute and then tried throttling again, then it started revving up like normal and everything was fine after that... I rode off like nothing ever happened.
I took the panels off when I got home and found that the exit port from the cylinder heat shroud was wet from blowby, the oil was sticky, not wet like a bad leak. I took the shroud off and the fins near the back of the cylinder (near the exit port of the shroud) were a little wet. I couldn't identify any other wet areas on the motor or carb.
A couple of things:
- The head bolts seemed pretty loose... Not handle-turnable loose, but it didn't take much force to unbolt the bolts. I looked at the manual and it said 7 ft/lbs which seems really weak. I pulled the head off and the piston top and head where clean/slightly-dry, no signs of detonation (pic attached below). I looked at the metal gasket, and it didn't really look like it was leaking from any specific area, but I changed it anyway just in case. Is it bad to torque the cylinder head bolts past 7 ft/lbs? I torqued it to 9 ft/lbs.
- I'm running a CHT sensor ring on the spark plug. The crush washer that comes with the plug was removed before installing. When I pulled the plug out there was a small amount of oil sitting on the top of the cylinder (very similar to the pic attached, photo was taken from one of Cmoped9's previous threads on here). The threads on the plug were wet from oil too. The plug itself seemed nicely browned, gauging from the plug-chop chart (pic attached, sorry for crappy focus).
Could it be that the engine lost compression at higher temperatures/rpms because of a small leak from the CHT sensor washer? And once the engine cooled down, the sensor resealed itself? It ran totally fine after which confuses me. Engine temps didn't exceed 275F so it didn't overheat either (maybe a faulty sensor?). IÔÇÖve never been able to get engine temps past 275F.
- The Daytona CDI IÔÇÖm running called for a plug 2-steps higher than stock during ÔÇ£racing-scenariosÔÇØ. Is running a 8-rated plug too cold for normal riding conditions? In addition, IÔÇÖm also using the original Tact spark plug cap and boot. Could this potentially be an ignition problem? I havenÔÇÖt had issues riding with this setup for the past 2-weeks.
- It also can't be a fuel issue since the engine idled after bogging and drove off once the motor was fine.
I've exhausted all of the potential scenarios I could think of... Based on the photos I posted, does it seem like the setup is running a little lean? It confuses me because my engine temps seem to be low which points towards being too rich up top, but at the same time the piston and plug don't seem to indicate running rich. Could all of this be caused basically by the CHT sensor leaking under high temp?
Let me know what you think.
The engine would still idle once stopping on the side of the road, but when I gave it any throttle, the engine would bog and almost stall. Once I let off, the engine would return to idle again. I waited a minute and then tried throttling again, then it started revving up like normal and everything was fine after that... I rode off like nothing ever happened.
I took the panels off when I got home and found that the exit port from the cylinder heat shroud was wet from blowby, the oil was sticky, not wet like a bad leak. I took the shroud off and the fins near the back of the cylinder (near the exit port of the shroud) were a little wet. I couldn't identify any other wet areas on the motor or carb.
A couple of things:
- The head bolts seemed pretty loose... Not handle-turnable loose, but it didn't take much force to unbolt the bolts. I looked at the manual and it said 7 ft/lbs which seems really weak. I pulled the head off and the piston top and head where clean/slightly-dry, no signs of detonation (pic attached below). I looked at the metal gasket, and it didn't really look like it was leaking from any specific area, but I changed it anyway just in case. Is it bad to torque the cylinder head bolts past 7 ft/lbs? I torqued it to 9 ft/lbs.
- I'm running a CHT sensor ring on the spark plug. The crush washer that comes with the plug was removed before installing. When I pulled the plug out there was a small amount of oil sitting on the top of the cylinder (very similar to the pic attached, photo was taken from one of Cmoped9's previous threads on here). The threads on the plug were wet from oil too. The plug itself seemed nicely browned, gauging from the plug-chop chart (pic attached, sorry for crappy focus).
Could it be that the engine lost compression at higher temperatures/rpms because of a small leak from the CHT sensor washer? And once the engine cooled down, the sensor resealed itself? It ran totally fine after which confuses me. Engine temps didn't exceed 275F so it didn't overheat either (maybe a faulty sensor?). IÔÇÖve never been able to get engine temps past 275F.
- The Daytona CDI IÔÇÖm running called for a plug 2-steps higher than stock during ÔÇ£racing-scenariosÔÇØ. Is running a 8-rated plug too cold for normal riding conditions? In addition, IÔÇÖm also using the original Tact spark plug cap and boot. Could this potentially be an ignition problem? I havenÔÇÖt had issues riding with this setup for the past 2-weeks.
- It also can't be a fuel issue since the engine idled after bogging and drove off once the motor was fine.
I've exhausted all of the potential scenarios I could think of... Based on the photos I posted, does it seem like the setup is running a little lean? It confuses me because my engine temps seem to be low which points towards being too rich up top, but at the same time the piston and plug don't seem to indicate running rich. Could all of this be caused basically by the CHT sensor leaking under high temp?
Let me know what you think.