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Old 10-14-2013, 06:47 PM   #1
Telo OP
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Location: Clifton NJ
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i think my bike is crapping out

So today i took my bike for a ride and noticed some smoke coming from my exhaust. Went home and later that day i went to start my bike up and go for a ride. The bike was incredibly hard to start and when i did get it starting it sounded like it was misfiring. Took the plugs off and both were fouled out, with oil on the spark plug threads and on top of the head where the spark plug sits. Anybody ever experienced something like this, seems like i need a rebuild. Any thoughts? Also i noticed that my intake tubes have oil coated on the inner surface.
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Old 10-14-2013, 07:12 PM   #2
JonnyCash
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I too think your bike is crapping out, but it would be helpful if you'd let us know what your bike is.
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Old 10-14-2013, 08:29 PM   #3
Telo OP
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oh yeah i forgot, its a 1971 r75/5
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Old 10-14-2013, 08:50 PM   #4
Kai Ju
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How is the oil level ? Overfilling the crankcase can give you the symptoms you describe. If it's not overfilled, what is compression/leak down ?

Not to mention some details such as mileage, service history, owner history etc.
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Old 10-14-2013, 09:25 PM   #5
Stagehand
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you using the sidestand? its definitly oil and not gas on the plug?

oil on top of the head where the spark plug sits, eh? Find out where thats coming from, thats not a great sign, in and of itself
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Old 10-15-2013, 01:58 AM   #6
Plaka
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Quote:
Originally Posted by Telo View Post
oh yeah i forgot, its a 1971 r75/5
The right intake tube is supposed to be oily. It get all the crankcase windage on that bike.

As the bike ages and gets more leaky, you may need one hotter plug to help burn off the crap---unless you really ride it when you go out. RPMs always over 3000 and ride it for a half hour. No short trips---those are really hard on it.

Wear doesn't happen abruptly, unless something flat out breaks. What does happen abruptly would be things you do. Tune-ups, oil changes, etc. These can cause an immediate change in how it runs. Mixing oil brands, or even weights of the same brand, can do odd things (usually smoking).
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Old 10-15-2013, 04:36 PM   #7
Telo OP
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well the bike has 30 thousand miles on it. Before i got the bike it was my uncles who had it for 15 years stored. I received the bike 2 years ago and worked on everything but the motor. Been riding it for a year and a half. i know that it burns some oil but to what extend, idk. I can tell you when i was replacing the head gasket, there was rust on the bottom of the cylinder core. And when i would rotate the motor, oil would past the rings, leaving a film on the bottom of the cylinder core.
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Old 10-15-2013, 04:42 PM   #8
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I think i see your problem.
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Old 10-15-2013, 04:55 PM   #9
Plaka
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Quote:
Originally Posted by Telo View Post
well the bike has 30 thousand miles on it. Before i got the bike it was my uncles who had it for 15 years stored. I received the bike 2 years ago and worked on everything but the motor. Been riding it for a year and a half. i know that it burns some oil but to what extend, idk. I can tell you when i was replacing the head gasket, there was rust on the bottom of the cylinder core. And when i would rotate the motor, oil would past the rings, leaving a film on the bottom of the cylinder core.
If the bores are rust pitted then it's gonna burn oil. Check your compression.

but a top end is good for more than 100k so if it was mine and that was the only problem, screw it, I'd just ride it. The power will be down a bit and you might need a hotter plug to cope with the oil, but it has an awful lot of life in it before it will need an over-bore and new pistons. Once it gets coked up the compression will come back up some, recovering a bit of performance.

Alternatively, you can have it bored and go to first over pistons now. There may be one other option depending on some things, but you would still have to buy new pistons.

Avoid any sort of synthetic oil.

I should add, rust is fluffy. A small amount of iron, by volume, makes a big volume of rust. So you can see a lot of rust but the pitting can be pretty minor. Unfortunately, pitting on the bottom of the bore is where the oil collects when the bike is at rest, so more oil getting into the cylinder right when you start up.

Plaka screwed with this post 10-15-2013 at 05:25 PM
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Old 10-15-2013, 05:36 PM   #10
DaveBall
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And yet again, Plaka is correct.

I would just ride it for a while and see how it goes. If oil consumption gets to bad, then seriously consider either boring the cylinders and new pistons, or see if I could find a good set of pistons and barrels. There are a lot of R75/5 out there. I bet a good set of jugs and pistons could be found for a somewhat reasonable price.
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Old 10-15-2013, 07:39 PM   #11
Telo OP
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if i were to decide on boring the cylinder, whats the max i can go to ( i was thinking 900cc). I can tell you that the bike burns oil to my dissatisfaction and I'm considering to install new rings and pistons since i have some money to throw at it. If i were to bore the cylinders to 900 then all i would need are pistons and a new set of rings, correct if im wrong? I know people out there installed 900cc pistons and kept the stock r75 heads. If i were to consider this option, how would I go about jetting the carbs.
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Old 10-15-2013, 07:56 PM   #12
lucky6600
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Originally Posted by Plaka View Post
Avoid any sort of synthetic oil.

Educate me please
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Old 10-15-2013, 08:36 PM   #13
Plaka
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Quote:
Originally Posted by Telo View Post
if i were to decide on boring the cylinder, whats the max i can go to ( i was thinking 900cc). I can tell you that the bike burns oil to my dissatisfaction and I'm considering to install new rings and pistons since i have some money to throw at it. If i were to bore the cylinders to 900 then all i would need are pistons and a new set of rings, correct if im wrong? I know people out there installed 900cc pistons and kept the stock r75 heads. If i were to consider this option, how would I go about jetting the carbs.
No way Jose. not enough metal. Most you can bore is 3rd oversize 750cc. There were some hop up kits for the 750 once that went a little bigger and used special pistons. Doubt they would be cost effective these days if you could find one.

You can fit early 900cc jugs and pistons to your block. I have done this. later 900 had a larger jug spigot so you would have to turn that down or open up the holes in the block.

If going to 900 you could use your 750 heads but I believe the 900 had larger valves so to take advantage of the bigger jugs you would want 900 heads too. I just went with a complete early 90/6 top end. Check me on that valves thing.

The 750 carbs will work fine for 900, just rejet w/ the stock 900 jetting. idles, mains and needles. That one is the cheap part. The specs are in the book.

Apparently the 900 block was stronger. I don't remember exactly. People told me my conversion would blow up. it never did, and I rode it hard.

You do want the clutch and starter in top shape when increasing power. but the 900 top end with the lower 750 rear end is big grins. Can be hard on alternator rotors, it accelerates pretty hard. The kick starter will still work, but don't do it barefoot (Gawd was that stupid!)

Getting into a full 900 top end (heads/jugs/pistons) used from a reputable source (ie, low mileage in good shape. NOT eBay) can cost about what a set of factory new pistons would. But if you have to do headwork it can get costly and you have only your 750 heads to sell off. Jugs and pistons worth only a little given their condition.

brand new pistons will come with rings. @30k the bottom end isn't even worth looking at.
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Old 10-15-2013, 08:42 PM   #14
Telo OP
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ok sounds like alot, im just hopping that this rust will come of without going over-bore, guess i wont find out till i pull the jugs off and get it checked
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Old 10-15-2013, 08:43 PM   #15
Plaka
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Originally Posted by lucky6600 View Post
Educate me please
Synthetics have a reputation for leaking through things non-synthetics won't. Old seals. Pitted bores, etc. They are just really slippery. Manufacturers have been working on it and supposedly it's better than in the early days of synthetics. Personally I don't attempt them in anything that doesn't have really good seals running on really good metal. I just tried a synthetic gear oil in the rear drive. New seal on old metal. Walked right past the seals. Cleaned it out and put in dino.
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