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'92 K75RT engine lifespan ?

scoobs

scoobs

New member
My k bike has 134,000 miles on it and the gas mileage has really dropped in recent years to a miserable 35 mpg/180 miles per tank. I used to get 50 + mpg/240 miles per tank when I first bought the bike with 70,000 miles on it. A recent inspection showed oil fouling on one of the spark plugs some I'm thinking it might need new piston rings ? If you add ongoing starter sprag clutch problems ( bike runs 2,500 miles before I need to do a Motormedic flush- I feel it needs a proper tear-down to clean things properly. I've been advised that will run around $600 for labour plus any parts that might be needed.) then I'm wondering if it would be more advisable to install a used engine ? I've found one for $450 + $250 shipping that has 55K miles on it- I'd still have to install it but it should solve both problems. It seems a better option from a financial point of view - anyone have any thoughts on this ? I understand the effects of wear and tear but have heard of K's with several hundreds of thousands of miles on them and wondered what was considered normal ?
Cheers,
Scoobs.
 
Before I did anything else I would have compression and leakdown tests performed to better determine the condition of the engine. Having put 370,000 on a K75 before it was wrecked I consider engine problems at 134,000 as premature. If that one cylinder comes up with what seems to be a ring leak then I would try to get that cylinder examined with a borescope to see if damage to the Nikasil cylinder was evident. This is rare but has happened. If that can be determined then a different engine is the way to go. Otherwise, it depends on what the results of theleakdown test are.
 
+1 on a leakdown test. Anything is possible, just because some engines go forever does not mean others won't go belly up a 100k. Maybe the original owner used the wrong brand/weight/type oil :rolleyes Generally, I would say old bricks succumb to other issues before the engine wears out. Replacing with a used is is a bit of a gamble but probably much more cost effective than rebuilding a bad one.
 
My '87 K100 has 154,000 miles and gets only slightly less gas mileage as when I bought it at 77,000 miles. There was a time when the mileage dropped, but then I realized that my right wrist was becoming much less inhibited than during my first three years of riding it. Once I got back to smoothly rolling on the throttle, the gas mileage returned close to what it used to be.
 
scoobs said:
My k bike has 134,000 miles on it and the gas mileage has really dropped in recent years to a miserable 35 mpg/180 miles per tank. I used to get 50 + mpg/240 miles per tank when I first bought the bike with 70,000 miles on it. A recent inspection showed oil fouling on one of the spark plugs some I'm thinking it might need new piston rings ? If you add ongoing starter sprag clutch problems ( bike runs 2,500 miles before I need to do a Motormedic flush- I feel it needs a proper tear-down to clean things properly. I've been advised that will run around $600 for labour plus any parts that might be needed.) then I'm wondering if it would be more advisable to install a used engine ? I've found one for $450 + $250 shipping that has 55K miles on it- I'd still have to install it but it should solve both problems. It seems a better option from a financial point of view - anyone have any thoughts on this ? I understand the effects of wear and tear but have heard of K's with several hundreds of thousands of miles on them and wondered what was considered normal ?
Cheers,
Scoobs.
Click to expand...

Don't discount the effect of Ethanol fuel on your mileage. In the area where I live, I get a solid 5 MPG less in all my bikes than when I buy fuel in several areas I travel through which are about 400 miles from here. This has been consistent for the last five years or so, but was not always the case. Also, have you have had the CO adjustment done, or checked the air bypass hose, or any of the other rubber bits in the intake track?

The sprag clutch is a puzzle. What motoroil do you use?
 
After chatting with a service tech. today I'm going to replace the water temperature sensor- I know it works as the cooling fan cut on several times this afternoon while idling in traffic, however was told that if it is adrift by even 10 degrees it can cause the mixture to run too rich and increase fuel consumption. I did test it last year by measuring the changing output resistance as the engine temperature increased but didn't accurately track the actual values- just kind of "ballparked the figures" to prove it varied with temperature change.
I'm aware that ethanol in the gas can reduce mpg by around 5% but I'm seeing a difference of almost 15 mpg so believe there is something wrong somewhere. I don't consider myself a speed merchant and normally ride fairly smoothly- however am prone to cracking it open for overtaking etc.
Thanks for your comments, I'll keep you updated once I get the new sensor installed.
Cheers,
Scoobs.
 
scoobs said:
After chatting with a service tech. today I'm going to replace the water temperature sensor- I know it works as the cooling fan cut on several times this afternoon while idling in traffic, however was told that if it is adrift by even 10 degrees it can cause the mixture to run too rich and increase fuel consumption. I did test it last year by measuring the changing output resistance as the engine temperature increased but didn't accurately track the actual values- just kind of "ballparked the figures" to prove it varied with temperature change.
I'm aware that ethanol in the gas can reduce mpg by around 5% but I'm seeing a difference of almost 15 mpg so believe there is something wrong somewhere. I don't consider myself a speed merchant and normally ride fairly smoothly- however am prone to cracking it open for overtaking etc.
Thanks for your comments, I'll keep you updated once I get the new sensor installed.
Cheers,
Scoobs.
Click to expand...

The water temperature sensor you may need to replace is the one on the F shaped pipe coming off the top of the engine block. It is a dual element sensor - meaning - the fan working doesn't mean the ECU is seeing the correct engine temperature. They work off different elements in the sensor.

To measure the temperature values for the ECU - it's best done at the ECU plug. Someplace on the IBMWR K-tech pages there is a chart that shows water temperature vs resistance, and tells you which pin on the connector to measure at. Be VERY careful not to damage the fingers on the ECU connector - they are easily bent and about impossible to repair. The official way of probing that connector is to remove the back shell, and go in with something like an unfolded paperclip next to the wire until it touches where the wire is crimped into the finger assembly. Testing at this point means the entire circuit is tested. The measurement is taken from the connector pin to ground. On the sensor itself - the two halves are the output pins, ground is the shell.
 
Oh - one other thought. When is the last time you checked the valve adjustment? Too tight valves can cause a loss of power and excessive fuel use.
 
deilenberger said:
The water temperature sensor you may need to replace is the one on the F shaped pipe coming off the top of the engine block. It is a dual element sensor - meaning - the fan working doesn't mean the ECU is seeing the correct engine temperature. They work off different elements in the sensor.

To measure the temperature values for the ECU - it's best done at the ECU plug. Someplace on the IBMWR K-tech pages there is a chart that shows water temperature vs resistance, and tells you which pin on the connector to measure at. Be VERY careful not to damage the fingers on the ECU connector - they are easily bent and about impossible to repair. The official way of probing that connector is to remove the back shell, and go in with something like an unfolded paperclip next to the wire until it touches where the wire is crimped into the finger assembly. Testing at this point means the entire circuit is tested. The measurement is taken from the connector pin to ground. On the sensor itself - the two halves are the output pins, ground is the shell.
Click to expand...

I HIGHLY recommend using that chart for the resistance values of the temp sensor as Don says. It saved me from doing a while lot of work when the problem turned out to be something else. Here's the link: http://www.ibmwr.org/ktech/gas-mileage.shtml
 
scoobs said:
After chatting with a service tech. today I'm going to replace the water temperature sensor- I know it works as the cooling fan cut on several times this afternoon while idling in traffic, however was told that if it is adrift by even 10 degrees it can cause the mixture to run too rich and increase fuel consumption. I did test it last year by measuring the changing output resistance as the engine temperature increased but didn't accurately track the actual values- just kind of "ballparked the figures" to prove it varied with temperature change.
I'm aware that ethanol in the gas can reduce mpg by around 5% but I'm seeing a difference of almost 15 mpg so believe there is something wrong somewhere. I don't consider myself a speed merchant and normally ride fairly smoothly- however am prone to cracking it open for overtaking etc.
Thanks for your comments, I'll keep you updated once I get the new sensor installed.
Cheers,
Scoobs.
Click to expand...

I have to say that I've never gotten 50mpg or even close to that with a K75. However, there are different riding styles. How would you describe your riding style, and how long ago was it when you did get those kind of mileages?
 
GREGFEELER said:
I have to say that I've never gotten 50mpg or even close to that with a K75. However, there are different riding styles. How would you describe your riding style, and how long ago was it when you did get those kind of mileages?
Click to expand...

That was my experience with my K75S - it actually got a bit worse mileage than my '85 K100RT did, and that was fairly awful. On average - I'd guess around 38MPG unless I was on a trip and stayed near the speed limit, then it would just barely get 40MPG.

I actually ride considerably faster on my current bike (R1200R) and get much better mileage. It's not hard to get 45MPG from it, and I've seen 55MPG on a trip. The difference is a much smarter fuel injection system. It also makes a bunch more HP.. :)
 
deilenberger said:
That was my experience with my K75S - it actually got a bit worse mileage than my '85 K100RT did, and that was fairly awful. On average - I'd guess around 38MPG unless I was on a trip and stayed near the speed limit, then it would just barely get 40MPG.

I actually ride considerably faster on my current bike (R1200R) and get much better mileage. It's not hard to get 45MPG from it, and I've seen 55MPG on a trip. The difference is a much smarter fuel injection system. It also makes a bunch more HP.. :)
Click to expand...

I can get 40 to 45 with my K75S at 75 to 80, but pushing above that or bucking a head or side wind and it will drop to the high 30's. But, that gives me about 200 miles to a tank which is acceptable, and I just love that bike.
 
My 1990 K75RT gas mileage varies quite a bit due to different riding styles and speeds, of course.
Cruising steadily at say 65-70 it averages about 40- 44 Mpg
Riding with friends in the canyons with a lot of full throttle bursts and full throttle running it can easily get down to 30- 35 Mpg
This is with a well tuned engine.
 
GREGFEELER said:
I can get 40 to 45 with my K75S at 75 to 80, but pushing above that or bucking a head or side wind and it will drop to the high 30's. But, that gives me about 200 miles to a tank which is acceptable, and I just love that bike.
Click to expand...

Mine too, and I can touch 50mpg if I can hold 65mph, but it has dropped some in it's old age. Nobody has addressed the fouled plug yet. I'd be curious to see a compression test at least.
 
35634 said:
+1 on a leakdown test. Anything is possible, just because some engines go forever does not mean others won't go belly up a 100k. Maybe the original owner used the wrong brand/weight/type oil :rolleyes Generally, I would say old bricks succumb to other issues before the engine wears out. Replacing with a used is is a bit of a gamble but probably much more cost effective than rebuilding a bad one.
Click to expand...

Is the plug oily or sooty? If it is sooty, I would move the injector for the fouled plug to a new position to see if the plug fouling follows the injector. You could have a leaking injector that over-fuels a cylinder. Also check the resistance of the plug wire to see if you have a weak spark. If all the other things like valve clearance and temp sensors check out, I would look at the air-fuel ratio. You can check that at fast idle and going down the road with a portable 3 gas analyzer. If the a/f is rich, there is an excellent article in IBMWR on how to adjust the air metering flap.

If the plug is oily, it could be valve guides, guide seals, or rings on that cylinder. I would also check the air box to see how much oil from the breather is entering the box.
 
beemerchuck said:
Also check the resistance of the plug wire to see if you have a weak spark. If
Click to expand...

It's a K75. You can not check the resistance of their plug wires because they have an internal gap. They will just show as an open.

A rough way to check fuel mixture:

1. warm motor to operating temp

2. while engine is running, push starter button. If idle increases, engine is running lean.

3. while engine is running, insert altitude plug. If idle increases, engine is running rich.

4. ideally, both tests should cause a slight drop in idle or at worst, no change.




:dance:dance:dance
 
update...

Thanks for the additional suggestions- I replaced the temperature sensor but it made no difference to my gas mileage so I think my next action will be getting the compression checked, then I can decide whether repair or replacement will be the most economical option. I may have to splash some cash on roof repairs to the house so the whole thing might be put on hold for a while. Fortunately I hae a second bike :)
Any further suggestions will be eagerly accepted......
Cheers,
Ian.
 
compression/leakdown test results...

Had a compression test done and 1 & 2 cylinders showed 170 (psi ?) while 3 was only 150, I had suspected there might be a problem due to discolouration of number 3 spark plug. The leakdown test came back at 15% for 1, 18% for 2 and a massive 30% for cylinder number 3- obviously there are serious wear issues going on that aren't going to get better.
My options now appear to be replace the engine with a decent used one, rebuild the pistons/rings/cylinders etc. or run the bike as it is. I have a lot of sweat and tears involved in this bike and would prefer to keep it running- anyone care to comment on the economics of these options? I'm sure there are several used engines out there but I'd have to find a lower mileage unit that had been compression tested before committing in that direction.
Cheers,
Ian.
 
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