Honda BF75 - Threw a rod!

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sandiegofisher

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Sep 8, 2002
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And the saga coninues... About 86 model BF-75 4-stroke Serial # above 7100001<br /><br />After replacing the fuel pump, oil pump, head gasket and after cleaning all the carbon and salt water buildup in the crankcase & valves, readjusting float, timing and spartk plug gap. I finally get this thing running nicely... for about 20 minutes.<br /><br />It developed a loud knock and then threw a rod bolt right through the crankcase cover! Upon inspection (through the gaping hole left) I discovered one of the connecting rod bolts had worked loose. Apparently whoever worked on this engine before me did not put the tab-lock washers in.<br /><br />No.2 cylinder still intact but lacks this washer too. Nothing else appears to be damaged just crankshaft cover and the bolt that got shot out. <br /><br />I can get a used replacement cover but was wondering if the pieces could be welded back on? And would also like to know what else I should check while I've got it torn down.<br /><br />Are these missing Tab-Lock Washers the cause or is it most likely something else? The engine turns by hand and is not siezed. A major set back in getting this old Honda running.<br /><br />Thanks again for all the help. You've gotten me this far and I'm not ready to give up on it yet.
 
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hondon

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Re: Honda BF75 - Threw a rod!

I'm having a hard time getting a mental image of the crankcase cover.If you have thrown a rod thru the side of that case ,you are done and that's all there is to it.In any sceneario , the crank is likely wasted and you are also done.I am very familiar with this engine and wiil help you if that ,s not how things are.
 
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sandiegofisher

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Re: Honda BF75 - Threw a rod!

Thanks for the reply Hondon...<br /><br />Since I am unable to attach an image to this post I will try to explain a little better. If you have the Sept 1987 issue of the Honda BF75/BF100 Service Manual you will see on page 63 the exploded view of Crankshaft/Piston assembly I am refferring to.<br /><br />The part that has the hole in it is the very top item in the drawing. (It's not labled but I call it the 'Crankshaft Cover', it exposes the bottom of the pistion rods when removed. It's the part of the cover that faces you when you are pulling the rope to start it. The piston did not leave the cylinder barrel, just one of the 2 cylinder connecting rod bolts that hold it to the crankshaft (2 for each cylinder connecting rod).<br /><br />There is supposed to be a tab-lock washer that spans the bottom of the connecting rod across the camshaft. It looks like a double ended boxend wrench and your supposed to bend the tabs on each end till they touch when installing. These are not present.<br /><br />The upper part of the crankshft housing which includes the cylinder barrel as well as the valve assembly seems to be fine and I seem to have good compression.<br /><br />I hope this explains it a little better and am looking forward to your response.<br /><br />Thank You! :cool:
 
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DJ

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Re: Honda BF75 - Threw a rod!

sandiegofisher,<br /><br />If this engine were turned, as it sits in a car, it sounds like you're talking about what would be the oil pan in a automotive application?
 
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sandiegofisher

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Sep 8, 2002
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Re: Honda BF75 - Threw a rod!

Yes. If it were a car motor that would be the oil pan. But this engine sits up on it's end vertically and therefore not much oil is located here therefore I'm a bit unclear as to how the camshaft is lubricated. Oil is getting to the valves but this area is fairly dry. That is to say there is a film of oil bybass but it's not wet with oil.
 
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DJ

Guest
Re: Honda BF75 - Threw a rod!

sandiegofisher,<br /><br />I do not know if that pan is steel or aluminum. If is not destroyed, you can probably repair it.<br /><br />The camshaft should get oil. It does not need as much as a crank. The loads are not as high and it rotates at 1/2 the speed of the crank.<br /><br /> I do not know how that engine gets oil to the cam.
 
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sandiegofisher

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Re: Honda BF75 - Threw a rod!

Djohns19,<br /><br />Thanks for the reply....<br /><br />It appears to be aluminum or some kind of casted aluminum. I have the 2 pieces that flew off and can have them welded here at work (I work for a custom yacht builder). The weld shop here can weld just about any kind of material. The hole is about 3 inches in diameter. If it can't be welded, then I have a source nearby for a used replacement.<br /><br />I don't think it is destroyed (it was at idle speed when it went) but I have'nt removed it and inspected other than looking through the hole with a flashlight. I'm pretty sure the Crankshaft is still good. If anything else was damaged I would suspect maybe the bottom half of the piston connecting rod assembly and possibly, but doubtful, the camshaft bearings. What other parts do you suggest I check?
 
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DJ

Guest
Re: Honda BF75 - Threw a rod!

sandiegofisher,<br /><br />If the rod DID NOT become disconnected from the crank, I do not think that anything topside (cam & valvetrain) should be affected.<br /><br />Take a very close look at the crank and make sure you secure all of the rod bolts. I don't think the rod is bent. But, if you want to get in that deep, it would be a good idea to have it checked and magnifluxed (looking for cracks).<br /><br />Do you think those retainers fell off, or were never installed? If the fell off, they're somewhere and could cause problems down the road.<br /><br />Good Luck! Keep us posted.
 
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sandiegofisher

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Re: Honda BF75 - Threw a rod!

djohns19,<br /><br />The rod is still connected by one bolt. I don't think the washers where installed in the first place and can't see how they could just fall off since they are bolted down unless they were istalled incorrectly. I can account for all 4 bolts. 3 are still in place and I have the one that came out.
 
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KeltonKrew

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Jul 31, 2002
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Re: Honda BF75 - Threw a rod!

I've read all your post's concerning this motor. IMO, this damn thing is HAUNTED!<br /><br />Good luck with it. You have much more patience that I do!
 
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DJ

Guest
Re: Honda BF75 - Threw a rod!

sandiegofisher,<br /><br />I'd say-GREAT!!<br /><br />Put it back together, sans-pan and turn it over slowly to make sure everything looks good in the crankcase. Then put the pan on and give it a whirl!
 
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digimortal777

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Jun 25, 2002
Messages
214
Re: Honda BF75 - Threw a rod!

its very odd that one of those hondas would give trouble , my dad had the 10 hp model (exact same engine as 7.5)<br />it was damn near bullet proof , then he sold it and got a yam 15
 
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Hooty

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Oct 2, 2001
Messages
4,496
Re: Honda BF75 - Threw a rod!

Someone has obviously been in the engine before you (no locking tabs) so as long as you have the crankcase off of the engine, I'd replace ALL the rod bolts and install the locking tabs. You don't if the bolts in there now are torqued right or if they've been stretched (over torqued). New rod bolts are cheap insurance.<br /><br />c/6<br /><br />Hooty
 
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