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Post by dashrite on Aug 25, 2014 19:42:00 GMT -5
Today my new 70cc bbk locked up on my Vento. I heard a metallic grind like a bearing sounds when it goes up then bam. Stopped. I took off my reed valve to look inside and found little metallic flakes sitting inside. there was oil on the cylinder and the crankshaft so I know it was getting oil. The premix was done right. I went over 250 miles going 30-35mph to break the cylinder in. My guess is the wristpin bearing. I replaced it with a new one. When I put the new cylinder on. This really sucks balls I can't afford a new cylinder kit and now i'm stuck bumming rides again for work and taking the bus life's a bitch right. It just sucks when I went to all this trouble to replace it after It locked up 2 weeks ago when the oilpump went up. I have to wait for this weekend to take it apart to find out really what happened. Sorry had to vent a little cuz I'm pissed. Nothing that can't be fixed though as always.
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Post by 2TDave on Aug 25, 2014 19:52:56 GMT -5
If the cylinder was getting fuel and oil I'd have to think a circlip failed or a defective bearing. If it's an iron cylinder chances are it can be honed and you'll just need a piston and rings. Won't know until you pull it apart though. Sorry man that really sucks!
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Post by Jwhood on Aug 26, 2014 11:39:09 GMT -5
Damn bro that sucks hope you find out what went wrong!!!
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Post by dashrite on Aug 26, 2014 20:43:11 GMT -5
I removed the cylinder and sure enough the wrist pin bearing exploded. i have little rods in the bottom of my casr. my question now is do i have to replace the crankshaft? it moves freely without hesitation but i don't know if they did any unseen damage.
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Post by Jwhood on Aug 26, 2014 21:57:22 GMT -5
I wouldn't think it would've done damage is there any excessive play in the rod near the crank and did you get all the bearing rods out of the engine that feel out the wrist pin??
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Post by dashrite on Aug 26, 2014 22:07:57 GMT -5
no there isn't any excessive play. I got out what i could see. I am going to use a magnet to get what ever else I can get out like the little metal flakes that are everywhere. I'm sure that would wear done some parts if I don't get them out. I need to order a new cylinder and piston. they are torn up. I'm also going to order a really good wristpin bearing. Not sure which bbk to buy now.
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Post by Jwhood on Aug 27, 2014 0:24:49 GMT -5
Which one was you running when this catastrophic failure happened??
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Post by dashrite on Aug 27, 2014 19:01:51 GMT -5
One of Docs bbk. The wristpin bearing I got from parts for scooters. I'm either going to buy a malossi kit or the Stage 6 streetrace.
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Post by 2TDave on Aug 27, 2014 19:31:53 GMT -5
Were the clips still in the piston?
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Post by dashrite on Aug 27, 2014 21:03:00 GMT -5
yeah they were still in
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Post by 90GTVert on Aug 30, 2014 12:15:52 GMT -5
Look at the inside of your conrod's small end for wear and check it's bore vs service manual specs.
Either use brake parts cleaner or flush the cases with gas or kerosene to be as sure as you can that little bits are out of the bearings. Then squirt some 2T oil into each and rotate everything around before you let it sit. Seal off the cases with rags or something.
So far I've only blown apart one needle bearing and that was at around 11,000RPM with either a stock or stock-level replacement. Wiseco makes a bearing that works for the 12mm pin engines with 70cc kits (too wide for stock pistons). B1043
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Post by dashrite on Aug 30, 2014 19:38:24 GMT -5
Great advice Brent. I wasn't sure as to which bearing to use either. I saw stage 6 had some that looked pretty beefy. Wiseco sounds better. I will check the bore size. I hope I don't have to replace the crank. I really don't feel like splitting the case and putting new bearings and seals in. Thanks
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Post by usmcdoc on Aug 30, 2014 21:42:52 GMT -5
My thoughts.. Ok the bearing you got from the vendor was a stock 2T bearing and would have these measurements.. www.ebay.com/itm/WRIST-PIN-BEARING-10mm-X-13-8mm-X-12-6mm-for-FOR-JOG-MINARELLI-2-STROKE-MOTORS-/181327551870?pt=Other_Vehicle_Parts&hash=item2a37f6dd7eThat is a stock 50cc bearing. 70cc BBK need a wider bearing so you don't have lateral slop/play. The bearing must bear nearly a tight fit inside the piston. Therefore the bearing size you should have used would be this one..which is a standard size for the 70cc BBK. Was this the bearing size you used? www.ebay.com/itm/171245381478?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AITIf not that would put stress on the bearing in 2 directions...up/down and of course laterally which would cause it to fail. I have yet to see one of the 30+ BKK's I have sold fail. But then that did not fail..it was the bearing as you said. Make sure if you are able to reuse the kit..or if you buy a new brand of kit that you get the right size bearing. That is the reason the sell the 2T bearings in 3 different widths. Just my 2 cents as I have used ...installed and sold many of those kits. I guess I should have put a disclaimer that a wider bearing needs to be used with a BBK. Sure...I have seen many get away with using the narrow stock bearing on a BBK. But I always use one that is wide enough to disallow any lateral play/slop. Is what I am saying and showing in the bearing size links above on Ebay...making any sense? The bearings will naturally have some play in their up and down motion...but when you allow lateral play as well..it REALLY puts a load on that tiny needle bearing. I am not am expert by any means..but I have built MANY BBK engines for myself and many customers as well..and I always used a bearing in which the width of proper size. Up/down + lateral play at the same time in the bearing sets up lots of vibration which will disintegrate those tiny bearings. Any input from anyone...think I am right?? Glenn
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Post by dashrite on Aug 30, 2014 22:26:56 GMT -5
Makes perfect sense to me. I did not know at the time that I would need a wider bearing size. I'm glad that you brought this to my attention so I don't order the wrong size bearing again. I should have researched a little more before ordering it last time. This kit is toast and unfortunately I have to buy a new kit now, but this time I will be ordering the right size bearing thanks to this information. I don't know which bbk to go with now. Thanks for that information Doc I never realized the width of the bearing that I ordered.
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Post by usmcdoc on Aug 31, 2014 8:12:27 GMT -5
Yeah...sadly when a needle bearing goes...those tiny pin bearings scatter and eat up the top end.. Good thing it was not an MHR or Polini kit huh?.. But yes be mindful of bearing size and fit..those little things take a lot of pressure and abuse from the high output of a BBK. Still curious if anybody agrees with my above post..and was looking for input. I may be wrong and I am always hoping to learn and gain insight...so I can provide better service to customers... Glenn
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