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80* EGT difference at idle and low RPM's?

T

TheBreeze

Well-known member
Sled is a 2010 M8 Boondocker Turbo. I rebuilt the top end this summer due to a wrist pin circlip that came out of the PTO piston and gouged through the nicasil on the cylinder wall on its way out.

I installed new pistons, rings, wrist pins, wrist pin bearings, circlips, base gasket, o-rings, replated the PTO cylinder, and had the MAG cylinder re-cross hatched. During that process, I installed a KOSO egt gauge to supplement the A/F gauge that came installed on the sled.

The motor fired right up after the rebuild, idles normally, and revs up just fine on the stand. However, the PTO side consistently idles 70-80* hotter than the mag side on the EGT gauge. The temperature difference holds solid when I increase the RPM's on the track stand (Ive only had it up to about 5500 rpm's)


I have tried swapping the EGT probes around, and the temp difference stays consistent the PTO side. I have also sprayed a bunch of starting fluid around the PTO crank seal, reed boots, base of cylinder, etc with no noticeable increase in RPM's indicating an air leak.

I also bypassed the boondocker box and temps remained the same.


My 08 M8 would always run much closer temps from side to side, which has me worried about the integrity of this motor.

Is this something I should be concerned about at this point? Do EGT's tend to stabilize as the motor is broken in and run under load for a period of time?

If I need to tear back into this motor, now is the time.
 
My BBM8 always ran 50-60 degrees hotter on the PTO side. I guess I never got an explanation for it but everyone said it was normal, including the engine builder. Koso gauges also, but that shouldn't be the problem.
 
This is normal on the 2010. I like to use the trim feature if you are using a Boondocker box to alleviate the problem as best you can. Because your PTO side is essentially new it may have a tighter piston to cylinder clearance which will create a slight heat increase as well. I would trim it up with your controller and then watch it as it breaks in to make sure all is well.

Check your clamp area where the airbox goes onto the throttle bodies just to make sure you don't have some sort of air leak there causing a lean condition. I have seen a few of them that were blown off or leaking.

It also seems that when you get to riding RPM (6000 to 7500) they stabilize and then the PTO goes leaner again at top (8000 to 8200) RPMs.

Check compression to make sure it is consistent from side to side. The actual number is not as important as the closeness of the number from one cylinder to the other.
 
Thanks for the replies guys. I did check the compression, and it was about 145 PTO and 142-143 mag ('10 head at 600 ft.). I attributed the slightly higher compression on the PTO side to the fresh cylinder.
 
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I was putting a heat cycle into the motor last night on the stand, and have another question for you experts out there.

EGT reading seemed to come up more evenly from side to side while Idling, but the actual readings became very erratic. Sled seemed to be idling normaly, but temps would jump from 400 to 650 to 350 to 600 in consecutive gauge flashes. Once again, nothing like I have even seen on my previous M with the same type of KOSO gauge. Man I seem to be battling this thing. WTH? Any thoughts?
 
You can adjust your throttle bodies. Mine were running about 90 degrees off with the stock pistons and cylinders. It might have had something to do with my airbox design, but it was obvious one side was open more than the other. So I evened them out.
 
I wouldn't worry to much until you can actually ride it, seem farther off then that a quite a bit. The jumping is usually from being to rich and nearly fouling out.
 
wyoboy - you thinking fuel burning in the y pipe? Last night was the first time running the sled on the stand when it wasnt 80+ degrees out. It was closer to 40 for the first time in months. Maybe that had something to do with it?
 
The only time I have seen a egt drop like that was from fouling a plug with to much fuel, leaned it out a little and they didn't do it. My 09 m1000 egts where 150* off at wot, but I never switched them to check it. The newer cylinder could make the difference but should even out pretty quick. The one major thing that effects temps is the throw of the crank, if the pistons are not exactly 180* opposed to each other then one will run in a different timing postilion. AC sets the timing as if they are 180* but say the throw is off 2* (which is spec) if the other cylinder is advanced 2* it will usually run a tiny bit hotter, unless it goes way lean and starts putting all the heat into the cylinder instead of the pipe ( a detonation symptom ) If over fueling and the timing is retarted it will put more fuel into the pipe and also raise the temps. But at idle there is not a real good flow and it could be just a matter of intake and exhaust flow being better on one side. As you can see lots of factors here, but I wouldn't be to worried about 80* difference.
 
I would not worrry about it Matt. Get a few good runs on it first to get everything broke in. Very little things can vary the temp and usually are not worth changing anything to get them even. The fuel pressure coming in from one direction can charge the one cylinder more than the other. Little differences in the reeds will cause differences in temps, intake throat slides only have to be off a few thousands to change things...the list goes one.
 
Sled is a 2010 M8 Boondocker Turbo. I rebuilt the top end this summer due to a wrist pin circlip that came out of the PTO piston and gouged through the nicasil on the cylinder wall on its way out.

I installed new pistons, rings, wrist pins, wrist pin bearings, circlips, base gasket, o-rings, replated the PTO cylinder, and had the MAG cylinder re-cross hatched. During that process, I installed a KOSO egt gauge to supplement the A/F gauge that came installed on the sled.

The motor fired right up after the rebuild, idles normally, and revs up just fine on the stand. However, the PTO side consistently idles 70-80* hotter than the mag side on the EGT gauge. The temperature difference holds solid when I increase the RPM's on the track stand (Ive only had it up to about 5500 rpm's)


I have tried swapping the EGT probes around, and the temp difference stays consistent the PTO side. I have also sprayed a bunch of starting fluid around the PTO crank seal, reed boots, base of cylinder, etc with no noticeable increase in RPM's indicating an air leak.

I also bypassed the boondocker box and temps remained the same.


My 08 M8 would always run much closer temps from side to side, which has me worried about the integrity of this motor.

Is this something I should be concerned about at this point? Do EGT's tend to stabilize as the motor is broken in and run under load for a period of time?

If I need to tear back into this motor, now is the time.

if the probes are not inserted the exact same distance into exhaust they will read different
 
if the probes are not inserted the exact same distance into exhaust they will read different

you hit it right on the head, throw the egt numbers aside and set the engine by plug color then go back and see what the egt's read,way better off!!!!
 
my egts read different too, its normal, it can jump from 0-200 degrees different.
when i first installed my turbo, sled was brand new as well, my frist ride the temps were all over for the first few miles, i would just make sure you dont go over the 1300 mark, if the cylinders are 200 degrees difference its not a huge deal, like others have said, you can use the trim on the bd box.

every sled ive ever owned the pto side always ran hotter
carbed or efi
 
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