acceptable evo compression 85 flhtc.
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Elite HDF Member
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acceptable evo compression 85 flhtc.
i'm seriously thinking about a total engine rebuild. one shop, i was told top and bottom with the motor at 100,000 miles. another said just the top end. i have about 100 pounds of compression, motor warmed up and throttle open. with a squirt of oil in the cylinders i get about 130. it uses about a quart of oil every 600 miles most of it coming out of the breather. the thing is it runs so good i'm on the fence on what i should do. top and bottom, just the top or leave it alone all together. i'm not a hot rodder and don't care about horsepower and it's basically a totally stock motor except for the original lifters were replaced several years ago.
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From: ct
Well,it's possible you could cut down the breather oil by maintaining the oil level half quart low at all times,that's where I run mine and some of the others. Full level tends to be too much oil. Compression is not too bad for that many miles,it's in range.
If it doesn't smoke,knock or leak from the case gasket,you could probably get away with lifters,cam,bearing,heads done over,all new gasket of course. Base gasket is seeping also then pull jugs also and refresh them,new piston and rings to match. Bottom end will add big time to the cost and may not be necessary at this point...
Also...your bike is a bottom breather,try running lower oil level and see what this does for your oil consumption first thing....just to see,you may be surprised.
If it doesn't smoke,knock or leak from the case gasket,you could probably get away with lifters,cam,bearing,heads done over,all new gasket of course. Base gasket is seeping also then pull jugs also and refresh them,new piston and rings to match. Bottom end will add big time to the cost and may not be necessary at this point...
Also...your bike is a bottom breather,try running lower oil level and see what this does for your oil consumption first thing....just to see,you may be surprised.
Last edited by glidein wide; Aug 21, 2017 at 07:07 PM.
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From: Upstate New York
I'll let you know when I wear mine out. 122,000 miles so far and counting.
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From: Bedford UK
With that sort of mileage, if you service the top end there is the risk of increasing load on the bottom end IMHO and wearing that out quicker. Either continue riding as it is or go the whole hog (sorry 'bout that!).
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that's exactly what i'm thinking. i'm leaning towards riding it as is for awhile yet. i'm going to recheck the compression numbers again today. it really depends on how hard i ride it and how much oil it uses.
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When I was a kid, I went with my dad out to some guy's farm. Not sure why we went, but the guy had this really, really old John Deere tractor that made quite an impression on five year old me. I thought it was the coolest thing ever. I can still close my eyes and hear it huffing and puffing.
The farmer saw me admiring it, and was kind enough to tell me all about it. I remember him saying "The best thing about these old tractors is that they keep running even after they're all worn out."
That's part of what attracted me to Evos. They are like that. There's something to be said for an old, tired, comfortable engine that just keeps running.
Anyway, my $0.02 goes like this: This is one of those engineering questions that's really a personal question. If you have the resources and the inclination, a full rebuild top to bottom is certainly a reasonable option. It may come to pass that you find that your lower end is fine. Or you may find that your big ends are all out of round, end play on the crank is out of spec, bearings are pitted, etc, etc, etc. There's no way to know without pulling it apart. Even if all the bearings check out, you'll still get a nicely balanced and trued crank out of the operation, which would be a plus.
It really depends on what you want out of the bike. If you're looking for something you can ride for 50k miles over the next five years, trust to carry you coast to coast, etc, that obviously tends toward a rebuild. If you're using it for local rides and you're never asking it to take you more than a couple hundred miles from home, that tends toward leaving it alone.
The farmer saw me admiring it, and was kind enough to tell me all about it. I remember him saying "The best thing about these old tractors is that they keep running even after they're all worn out."
That's part of what attracted me to Evos. They are like that. There's something to be said for an old, tired, comfortable engine that just keeps running.
Anyway, my $0.02 goes like this: This is one of those engineering questions that's really a personal question. If you have the resources and the inclination, a full rebuild top to bottom is certainly a reasonable option. It may come to pass that you find that your lower end is fine. Or you may find that your big ends are all out of round, end play on the crank is out of spec, bearings are pitted, etc, etc, etc. There's no way to know without pulling it apart. Even if all the bearings check out, you'll still get a nicely balanced and trued crank out of the operation, which would be a plus.
It really depends on what you want out of the bike. If you're looking for something you can ride for 50k miles over the next five years, trust to carry you coast to coast, etc, that obviously tends toward a rebuild. If you're using it for local rides and you're never asking it to take you more than a couple hundred miles from home, that tends toward leaving it alone.
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From: Bedford UK
I've owned my '90 from new and in its heyday (before I changed to an S&S engine) it would use around a US quart per 1,000 miles, although it didn't shed any of that oil through its breathers.
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i bought the 85 new in the spring of 85. it's had plenty of problems, electrical being the biggest. a valve spring broke under warrenty and took out the breather gear. that's the only thing that went wrong with the motor. one belt broke and the original belt had the teeth peeling off so i'm on the 3rd belt. i did all that myself but rebuilding the motor will be left to the engine experts if and when it goes in for that.