Bottom end condition

Bottom End (crankcases and crankshaft)
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Boneshaker74
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Joined: Wed Aug 27, 2014 8:31 pm
Bikes: 57 FL
54 FL

Bottom end condition

#1

Post by Boneshaker74 »

I'm rebuilding my 57 engine and hopefully only have to do the top end. I'm trying to determine the condition of the bottom end without having to take it apart. The front piston is moderately scored on it's front skirt and I'm trying to figure out why. I measured the con rod side shake and I came up with 0.07". The limit is 0.0937" so I have some room. The rear con rod is tighter. Very little up and down movement. I still have to measure the crankshaft end play to get a better idea of what I'm working with. Are there any other checks that I can do to determine the condition of the bottom end without taking the bottom end apart?



1951 adam
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Re: Bottom end condition

#2

Post by 1951 adam »

The problem some times with a fresh top end is it can push a marginal lower over the edge. I usually check for up and down movement in the rods, check rod side play with a feeler gauge , and check end play. While the tops off check that rods are square in the bores with jig. If it wasn't knocking before the rods are probably OK, better safe then sorry.
Adam

Boneshaker74
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Re: Bottom end condition

#3

Post by Boneshaker74 »

1951 adam wrote:The problem some times with a fresh top end is it can push a marginal lower over the edge. I usually check for up and down movement in the rods, check rod side play with a feeler gauge , and check end play. While the tops off check that rods are square in the bores with jig. If it wasn't knocking before the rods are probably OK, better safe then sorry.
Adam
Thanks Adam. That's very good advice.

nmaineron
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Re: Bottom end condition

#4

Post by nmaineron »

You don't say how long its been since it has had the lower done and given that it is down I would split the cases.I have seen too many marginally good lowers with pinion races well on their way out...from where you are at it isn't that big of a job to pull the pinion side off and give it a good look....

Bigincher
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Re: Bottom end condition

#5

Post by Bigincher »

I agree with checking out the lower end. You'll never have a better opportunity to do it economically.
A friend of mine several years ago bought a basket case '57 Big Twin. He knew the bike and it's history and knew the bottom end had been rebuilt, but the top end was never assembled. It sat like that for years.
When he finally did buy the bike, he had the cases split, only to find a large accumulation of dirt and gunk built up in there. All it needed wa a good cleaning. Had he not split the cases and taken a peek, it would've been a nightmare that would've ruined that motor for sure....

You say in your first post "very little up and down movement."
There should be ZERO up and down movement.

Boneshaker74
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Re: Bottom end condition

#6

Post by Boneshaker74 »

nmaineron wrote:You don't say how long its been since it has had the lower done and given that it is down I would split the cases.I have seen too many marginally good lowers with pinion races well on their way out...from where you are at it isn't that big of a job to pull the pinion side off and give it a good look....
I have almost no history on the engine at all. Sometime in the late 80's it was built into a stroker but I don't know if the bottom end was touched. I think you've convinced me to at least pull the pinion side and have a look.
Bigincher wrote:I agree with checking out the lower end. You'll never have a better opportunity to do it economically.
A friend of mine several years ago bought a basket case '57 Big Twin. He knew the bike and it's history and knew the bottom end had been rebuilt, but the top end was never assembled. It sat like that for years.
When he finally did buy the bike, he had the cases split, only to find a large accumulation of dirt and gunk built up in there. All it needed wa a good cleaning. Had he not split the cases and taken a peek, it would've been a nightmare that would've ruined that motor for sure....

You say in your first post "very little up and down movement."
There should be ZERO up and down movement.
Thanks for the info Bigincher. I had to go check the rods again and what I wrote in my first post was incorrect. There is no up and down movement at all. What I was noticing was rod side shake (within tolerance) and thought there was a bit of up and down movement but no.

I'll split the cases and report here.

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Re: Bottom end condition

#7

Post by 6hds »

I believe the HD shop manual shows a pic and says at BDC, 3/32" side play at the wrist pin is maximum. Gary

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