ipa
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Posts: 15
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Post by ipa on Sept 5, 2012 20:41:15 GMT
BACKGROUND: I have a 1987 FZ700TC about 6000 miles ago I tore the whole thing apart and rebuilt it with a "rebuilt" 750 I found. All has been well since then, but recently I went out to start the bike and oil was all over. I ride daily and a week before I had done some mods and put a small filter right on the crankcase breather. It looked like the oil had overflown there. I attached the breather tube and the filter on it and started it up to notice oil splashing from a small hole behind the breather hole. I went to look at the previous engine and see what was there... a bolt. I figured I would just swap it over to the current motor and that it had worked its way loose. When I pulled the bolt out of the old motor it is at least 6" long and there is no way it could have escaped with the gas tank in place... must have not been in the past 6000 miles and never overflowed before. I pulled the tank and went to install the bolt, it only goes in ~1.5" I have looked at the parts drawings and cannot tell from them what could be in the way.
QUESTIONS: Does anybody know what the bolt just behind the crankcase breather passes through before it reaches the threads? Any idea why it waited until now to spray oil out the hole?
Although it seems horrible to have this issue, the bike has been running great. I currently have the hole plugged, but am worried there may be something mobile in the crankcase that should be bolted in.
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Post by Crusty on Sept 5, 2012 21:02:40 GMT
The obvious question to ask is... can you find the thread in the missing hole? There's a possibility that the 6 inch long bolt has actually sheared off and most of it is still in there, losing the inch and a half that has fallen out.
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ipa
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Posts: 15
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Post by ipa on Sept 5, 2012 21:06:50 GMT
Crusty, thanks for the quick response. That was my first thought as well. However, I can poke something smaller quite a distance down through there, which is why I figured it was supposed to pass through something that may have shifted and is now partially blocking the way. Didn't want to cause any more damage, but I did try to push with a narrow screwdriver to possibly re-align whatever is in there, no luck.
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Post by skucera on Sept 7, 2012 4:57:29 GMT
Is it possible that your new breather filter restricts airflow more than the arrangement you had on before? Perhaps your new filter restricts the flow of air out of the breather hole, causing blow-by gasses to push oil out of that other empty bolt hole? Cars with warn rings are known for blowing oil past crankcase oil seals when blow-by is too great for the EGR system to cope with, and that's what I thought of when I read your description. Maybe you can try taking your new breather off and restoring the original breather to see oil stops bubbling out of that hole? Scott P.S.--Sorry about the unclear wording. I'm tired, and I feel like I can't write "to get myself out of a paper bag."
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ipa
New Member
Posts: 15
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Post by ipa on Sept 7, 2012 18:25:24 GMT
skucera, that is possible, but I have band-aided the issue by plugging the hole. It didn't happen for a week or so after I switched the filter, but I had dropped my jet needles down making the mid-range a bit leaner that day and that could have caused more heat which may have contributed to the issue. Mainly I was hoping to find somebody who has torn apart the crankcase and knows what that bolt passes through. I don't have the supplies to perform a leak down test to see if that's likely.
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