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Discussion Starter #1
I took the engine out of my F11 to rebuild the top end, and it doesn't look too bad. A little carbon, and some wear streaks on the sleeve but nothing striking. I have a compression test kit and I plan to test it tonight (and probably should have done this before taking it apart). Can anyone tell me what an acceptable range of pressure is for a 1975 F11B? The bike shows 9300 miles, and it felt strong. I don't want to do more work than I need to! I'm thinking just a set of stock rings at the most.

Jeff
 

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I took the engine out of my F11 to rebuild the top end, and it doesn't look too bad. A little carbon, and some wear streaks on the sleeve but nothing striking. I have a compression test kit and I plan to test it tonight (and probably should have done this before taking it apart). Can anyone tell me what an acceptable range of pressure is for a 1975 F11B? The bike shows 9300 miles, and it felt strong. I don't want to do more work than I need to! I'm thinking just a set of stock rings at the most.

Jeff
Anything above 90psi should be fine. Its going to be very difficult to test compression with the motor out of the frame. But if you already have it apart just have the cylinder and piston miked and you will know exactly what you need to do.
 

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Discussion Starter #3
Thanks. I found a std piston kit with rings, clips, and pin for 22 bucks brand new. A steal. I am going to drop that into the engine. I don't think I want to spend the time, money and effort to get it bored. It really looked ok. I'll let you know how it goes. I'll test the compression once it's back together, and hope for the best!

Do you know what type of oil I need in the gearbox? I also noticed a little oil inside the crank case. Should I drain that?

Thanks for the help...

Jeff
 

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You probably would want to lightly hone the cylinder, if you had not planned to that is. It will help those new rings to seat.

D~
 

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Discussion Starter #6
Yep. Originally I was not planning on a hone, but I did it last night. I used a 70mm flexhone and it was very simple and effective to use. Surprisingly, it was very difficult to get the new piston and rings into the cylinder. They were tight - especially the lower ring. I had to tap the assembly into the cylinder. I measured the ring gap on the new rings after the hone and came up with about .016 - tight, but not under spec from what I have read. The old ring gap was about .030. The piston seemed to free up a bit as it was installed higher into the cylinder, but it's still fairly tight. I verified i had the correct parts, and they were all marked standard. We'll see.
 

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"Measuring" is the only way to go when performing any rebuilding operations.
You will have to buy, rent, beg, borrow or steal any gauges needed and a shop manual to obtain proper specifications.
Some wear streaks on the sleeves? What does this mean?
What was the piston to cylinder clearance on the old piston?
What is the new clearance?
If the piston freed up higher in the cylinder, you must have some cylinder taper!
Do not put together until it is checked out.
The possibility of low compression is the least of the problems with engine destruction at the top of the scale.
Do not want to come across as hard nosed, but money does not grow on trees anymore, (at least in my house) so just trying to save you some!
 

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Discussion Starter #8
Well, I imagine after 9,000 miles there would be a little taper. It's a 2-stroke, so I am not worried about it burning oil really. The ring gap between the exhaust port and the top of the cylinder, as I stated was about .016 -.017 with the new ring, after the hone. It won't leak compression, that's for sure. I didn't measure the piston to cylinder gap, but I could - the head is still off. I'm more worried about it being TOO tight, but I don't know how that is possible unless I have the wrong parts.
 

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Discussion Starter #10
I will double check the part numbers on the three rings. I know the piston is marked with an S. The lower ring is the one with two parts, and that seems to be the tight one. What is the function of the inner ring on the lower ring groove...the thin, wavy steel band under the primary ring? Keeps the outward pressure on the lower ring? (I am pretty sure it is supposed to be on the bottom groove. Shop manual doesn't even show three rings)
 

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Do not want to come across as hard nosed, but money does not grow on trees anymore, (at least in my house)
There's your problem right there. Money tress have to be outdoors because they require a lot of sunlight and fresh CO2. :lol:
 

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Discussion Starter #12
According to the shop manual I have, the standard ring end gap spec is .0078 - .0157 with a service limit of .028. I measured about .017, so I am good there.
 

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That wavey thing is a ring expander and you may have it assembled incorrectly; hence it is tight. It can be very very easy to do and most everyone does it once. I can't say for sure as there are many different types out there.
It is always good policy to double check all clearances as sometimes things get goofed up somewhere and a piston that is stamped "S" is really .010" over. The rule is to "trust nothing, verify everything!"
 

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I am going to have to retract the "ring expander" as a certainty. I looked up the parts diagram and it is a little unclear how this is set up. Have not seen this type before, so hopefully someone can shed some light on how this is set up.
 

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Discussion Starter #16
I have that on the lower ring groove, under the ring. It seemed pretty straight fwd. I will check the clearances tonight.
 
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