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slight loss of horsepower after piston clean


Christo

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I recently replaced my head gaskets and did a thorough cleaning of the tops of the pistons. I'd say there was about 1/8" of carbon buildup in some places.

On the left side, which was the most heavily deposited with carbon, I removed the cylinder also and the piston rings and cleaned everything up more thoroughly.

 

I was especially careful to note the orientation of the Rings and make sure to get them with the correct lettering facing up and in the right order and at staggered 120 degrees gap spacing.

 

Just did a 400 mile round trip, and the bike runs great with no head gasket leaks, except I (think) I now notice a slight decrease in horsepower and a slight decrease in gas mileage (40ish before, now down to 38) on straight highway riding.

 

Was I getting higher compression and more power with the carbon deposits on the pistons??

 

It may also be that I need to adjust the valves since I had the heads out and on the bench and in different positions while I cleaned them. I planned on doing the valve adjust when I do the 600 mile retorque.

 

 

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Afternoon SnakePlisskin

 

 

What makes you think the it has less horsepower?

 

Does it have less top end speed or slower time 0-60 or 0-100?

 

Slightly less compression could effect your power a little but probably not enough to feel.

 

What else did you do to the bike or engine while you were working on it?

 

 

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If you are that concerned, do a leak down test.

 

I'm with Dirtrider, what makes you convinced you have less compression or horsepower?

 

Don't know the details of your service or repair, but if you didn't adjust valves I'd do so now after a head re- torque.

 

Did you do head work?

 

:lurk:

 

MB>

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DR, it just seems slightly less peppy. Not by much, kind of like when you're riding in cold air vs hot. Except that the last time that I took a trip on it it was hot outside, and now it's cold. Then when I had slightly less fuel economy, it seemed to add to that idea. Could be part imagination, part valve out of adjustment, part loss of compression.

 

The work I've done over the winter includes:

- Transmission swap (Replaced original M94 with M97 from '98 R1100RT)

- Head gaskets

- Left cylinder base gasket

- Thorough cleaning of the tops of both pistons, and ring lands on the left piston, which was more carbonized than the right. Turns out the ring lands were pretty clean already, but I just wanted to be sure based on the advice given.

 

I've taken the throttle bodies off several times for these jobs and the throttle cables have had tension on them several times I'm sure. But I did do a throttle body balance but no valve adjustment yet. It rides fine now, with minimal surging, just like before all the work started.

 

MB, I may do that test or other to make sure things are as they should be. I didn't touch the valves, except to clean off the surface carbon in the combustion chamber. There was not much carbon buildup on them and I felt there was no need to take the heads apart and get into all of that. The bike only has 40k miles. So I might do that down the road.

 

Just to clarify, its a '95 R1100RS.

 

I'm hoping the valve adjustment does the trick. The last time I did a valve adjustment and throttle body balance at the same time, my gas mileage went from 32 to 42mpg (it was running very rich before, and I presume this was the cause of the carbon buildup)

 

 

 

 

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Winter gas formulation will give you less MPG. If you're seeing a drop of 2-4 MPG between winter and summer it could easily just be the difference between winter and summer gas. (There's more gasoline in the summer mix and fewer other components)

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Guest Kakugo
Winter gas formulation will give you less MPG. If you're seeing a drop of 2-4 MPG between winter and summer it could easily just be the difference between winter and summer gas. (There's more gasoline in the summer mix and fewer other components)

 

That's your answer in a nutshell. :thumbsup:

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I hadn't thought about winter gas formulation. That may be it. I thought my car's mpg was a little lower also. Thanks.

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roger 04 rt
...

 

I'm hoping the valve adjustment does the trick. The last time I did a valve adjustment and throttle body balance at the same time, my gas mileage went from 32 to 42mpg (it was running very rich before, and I presume this was the cause of the carbon buildup)

 

 

Some things are going on with your bike but a couple things don't sound likely:

 

--that a valve adjustment changed your gas mileage by a third

--that a rich mixture deposited 1/8" of carbon on your piston

 

Does your bike have an O2 sensor?

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I'm curious why you didn't do a valve adjustment on reassembly? I also think the difference between summer gas and winter gas would easily explain your fuel mileage drop.

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:thumbsup:

With my boxers I always did valves before hooking up the Carbtune.

Plus it was usually at interval service time (mine stayed balanced and smooth) so oil/filter and or fluids filters.

All part of the routine.

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Some things are going on with your bike but a couple things don't sound likely:

--that a valve adjustment changed your gas mileage by a third

--that a rich mixture deposited 1/8" of carbon on your piston

Does your bike have an O2 sensor?

 

I've only owned the bike for a year and half. And my first oilhead. The bike was running rich for who knows how long due to settings made by a shop to eliminate all surging, at the request of the former owner. I got everything tuned with surging down to a slight level (comes and goes depending on weather, gas quality, etc.) But it was right after a TB Sync and a valve adjust I had my first no-surge, 42 mpg day.

 

I do have an O2. And a while back I went through all the tune up steps (computer code check, motronic voltage check, etc. - all normal) It has a Booster Plug but I find it doesn't affect surging very much, so I could live without it. Basically, I'm all about factory settings and equipment, proper tuning, and high gas mileage.

 

I'm curious why you didn't do a valve adjustment on reassembly? I also think the difference between summer gas and winter gas would easily explain your fuel mileage drop.

That's a good question. I probably figured I'd be back in there in 600 miles to retorque the head bolts and would do it then. I hope you and others are right about the gas.

 

 

Thanks Mr. Tallman for the advice. I need to incorporate it into regular service. It seems to make a big difference.

 

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Anytime you remove and refit the cylinder heads or retorque you must follow up with a valve adjustment. If the head is a couple thousandths (or even ten thousandths) closer or further from the camshaft, it will affect the valve clearances. If it's a bit closer, the clearances will close up causing changes in valve timing (opening and closing) and could result in leakage. If it's further away, the duration will be affected but at least it won't be leaking. If it were mine, I wouldn't be waiting for 600 miles to get at it. It's a critical adjustment and will affect all kinds of operational variables.

FWIW

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Anytime you remove and refit the cylinder heads or retorque you must follow up with a valve adjustment. If the head is a couple thousandths (or even ten thousandths) closer or further from the camshaft, it will affect the valve clearances. If it's a bit closer, the clearances will close up causing changes in valve timing (opening and closing) and could result in leakage. If it's further away, the duration will be affected but at least it won't be leaking. If it were mine, I wouldn't be waiting for 600 miles to get at it. It's a critical adjustment and will affect all kinds of operational variables.

FWIW

 

 

Evening Rawed

 

The BMW boxer 1100/1150 is slightly different as the camshaft is in a carrier that is bolted solidly to the cylinder head (basically the camshaft to cylinder head position doesn't change with head removal as long a the cam carrier isn't intentionally unbolted from the cyl head) .

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You are correct sir - my bad. I've actually done my own valve adjustments on my R1150 several times and I knew that. I'll put my mind in gear prior to responding next time.

 

Anytime you remove and refit the cylinder heads or retorque you must follow up with a valve adjustment. If the head is a couple thousandths (or even ten thousandths) closer or further from the camshaft, it will affect the valve clearances. If it's a bit closer, the clearances will close up causing changes in valve timing (opening and closing) and could result in leakage. If it's further away, the duration will be affected but at least it won't be leaking. If it were mine, I wouldn't be waiting for 600 miles to get at it. It's a critical adjustment and will affect all kinds of operational variables.

FWIW

 

 

Evening Rawed

 

The BMW boxer 1100/1150 is slightly different as the camshaft is in a carrier that is bolted solidly to the cylinder head (basically the camshaft to cylinder head position doesn't change with head removal as long a the cam carrier isn't intentionally unbolted from the cyl head) .

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roger 04 rt
Some things are going on with your bike but a couple things don't sound likely:

--that a valve adjustment changed your gas mileage by a third

--that a rich mixture deposited 1/8" of carbon on your piston

Does your bike have an O2 sensor?

 

I've only owned the bike for a year and half. And my first oilhead. The bike was running rich for who knows how long due to settings made by a shop to eliminate all surging, at the request of the former owner. I got everything tuned with surging down to a slight level (comes and goes depending on weather, gas quality, etc.) But it was right after a TB Sync and a valve adjust I had my first no-surge, 42 mpg day.

 

I do have an O2. And a while back I went through all the tune up steps (computer code check, motronic voltage check, etc. - all normal) It has a Booster Plug but I find it doesn't affect surging very much, so I could live without it. Basically, I'm all about factory settings and equipment, proper tuning, and high gas mileage.

 

...

 

SP, with a connected, functioning O2 sensor, the mixture richness/leanness is entirely under the control of the Motronic.

 

Do you think the O2 was reconnected during the tune process or is it possible that your coding plug was changed or altered?

 

With the O2 disconnected or with no coding plug, the mixture is richer at small throttle angles unless a CO potentiometer was installed; and also in that configuration the BoosterPlug will add fuel (which it doesn't if the O2 was effective).

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Winter gas is a thinner mixture of fuel (shorter chain length hydrocarbons) to increase starting performance in cold weather. The colder the air, the more dense it is and the more fuel required to maintain the 14.7:1 air/gas mixture based on molecules per displacement volume. In colder weather you will use more gasoline because the BTUs available for energy is less per volume of gasoline and it takes more gas to get the correct mixture.

 

I purchase automotive fuel without ethanol for our airport and have to be mindful of the amounts on hand of Winter gas not carried over for Summer. High temps from air cooled engines can actually begin to boil the Winter gas in the fuel lines with potential of starving the engine of power.

 

Valve lash will affect compression and power available especially if it out a few thousandths. More dense Winter air is another factor in power needed to overcome flat plate drag just like running through the air vs water as an extreme comparison.

 

The O2 sensor is responsible for leaning correctly but most of its value is at or near idle. Wide open less involved or less critical. It should make a difference of about 3 to 6 ounces per tankful.

 

Another thing commonly overlooked in Winter is low tire pressure and that too will make gas mileage sour.

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SP, with a connected, functioning O2 sensor, the mixture richness/leanness is entirely under the control of the Motronic.

 

Do you think the O2 was reconnected during the tune process or is it possible that your coding plug was changed or altered?

 

With the O2 disconnected or with no coding plug, the mixture is richer at small throttle angles unless a CO potentiometer was installed; and also in that configuration the BoosterPlug will add fuel (which it doesn't if the O2 was effective).

You make a good point. To be honest, I'm not sure what the dealer did to run the bike rich to address the surging. Perhaps fiddling with the crossover or even the choke cable? I was getting some sooty/rich exhaust before that seemed to disappear about the time I balanced the TBs. All other measurements were normal. I played with Booster Plug/no booster plug config. But I thought the mileage was still a little low. The valve adjustment actually came the next summer (July and 95 degrees F) and that's when I noticed the big jump in mileage.

 

In addition, there were interruptions in my riding such as moving, repairs, Winter, etc. And I can't pinpoint when the mileage jump happened. I will say that I only had to adjust one right side exhaust valve slightly, all the rest were fine. So the TB imbalance could have caused the bad mileage.

 

Also, I suspect the former owner did a lot of in town stop and go. So that and the TB imbalance may account for the carbon buildup.

 

I feel like I've gotten her on the right track now and am happy with the performance.

 

Rx_Mich, thanks for the input. Sounds like Winter gas is to blame. Interesting about ethanol's affect on air-cooled engines. And I'll check the valves again. I checked my tires the other day so I think they are good.

 

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terryofperry

Rx_Mich

 

Maybe I misunderstood your comment regarding the O2 sensor and its value, if so I apologize. I think data shows we are in closed loop much more of our ride than we think and at wide open throttle much less than we think.

 

Terry

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roger 04 rt

On the Oilhead, Closed Loop is below about 50% throttle and under roughly 6000 RPM, which means it affects about half to 75% of all riding. However, factors called Long Term Trims are calculated in the Closed Loop area and applied to the entire fuel map. So the effect of the O2 sensor is on all fueling.

 

Here's a plot of points where closed loop has been recorded:

 

R1150ClosedLoop4.jpg

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Thanks Roger...the map shows more coverage than I was aware of. It seemed to me more critical at the low end cause if not sensing, very easy to stall due to excessive lean in failure. At riding speeds, wasn't so much an issue when mine failed but it may be what was happening, heated system was beginning to work. If a defective O2 sensor in higher rpm don't know which wins... less power from excessive leaning requiring more throttle or better gas mileage from the leaning? :)

 

In aircraft engines (air cooled), too lean can cause cylinder overheating enough to fail but don't know how much control the O2 sensor has at 3000-4500 rpm range in motorcycles. Does it lean modestly, moderately or heavily at higher rpms? Map shows activation points O2 is involved but how much does it changes mixture in these ranges?

 

I was trying to account for fuel usage if O2 sensor circuit defeated due to failure and the circuit pulled where the mixture is on the rich side throughout the rpm range.

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