I NEED HELP WITH MY CON ROD SITUATION suggestions plz
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Enthusiast
2003 Derbi bullet 2 stroke
Joined: 09 Jul 2018
Posts: 73
Location: Texas
Tue Nov 27, 2018 4:14 pm quote
Well I have a couple of questions, is this ok or do I need a wider con rod? Of course I Gunna get wide ass bearing . Also if that's not ok can I grind this down to fit a wider rod or will that weaken the crank? The cylinder kit on this engine is a Athena Racing 70cc, crank is a bzm crank, crankcase is custom made. I can't fit a wider Rod on this crank without grinding that because than the crank will rub the crankcase. If I can't grind it then I guess I'll have to get a custom rod which btw who makes custom rods?

IMG_20181125_133635.jpg
This is the photo I was referring to when I said, is this ok?

FE5MPQHGSUT1Z0T.LARGE.jpg
This is what I wanna grind down

IMG_20181126_212439.jpg
Here's the crank

IMG_20181126_212256.jpg
Here's the crank in the case

Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and new to 2018, '66 Blue Badge Smallframe
Joined: 30 Nov 2011
Posts: 6499
Location: Victoria, Australia
Tue Nov 27, 2018 5:43 pm quote
Think about this - when the piston is located in the bore, how far sideways (relative to the crank) can it move?
Also - grab the conrod and see how far sideways (between the crank webs) it can move.

The answer is (in case you were wondering) is bugger all.
I wouldn't worry about it.
Enthusiast
2003 Derbi bullet 2 stroke
Joined: 09 Jul 2018
Posts: 73
Location: Texas
Tue Nov 27, 2018 5:47 pm quote
Ginch wrote:
Think about this - when the piston is located in the bore, how far sideways (relative to the crank) can it move?
Also - grab the conrod and see how far sideways (between the crank webs) it can move.

The answer is (in case you were wondering) is bugger all.
I wouldn't worry about it.
If I grab the rod and pull it as far as it can go (not forcing it) it will run against the crank, what would I do about that? Does that mean I have a bad big end bearing?
Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and new to 2018, '66 Blue Badge Smallframe
Joined: 30 Nov 2011
Posts: 6499
Location: Victoria, Australia
Tue Nov 27, 2018 6:06 pm quote
Is it actually touching the crank though? They normally have a spacer between the crank web and the conrod on both sides.

Clipboard01.jpg

Enthusiast
2003 Derbi bullet 2 stroke
Joined: 09 Jul 2018
Posts: 73
Location: Texas
Tue Nov 27, 2018 6:09 pm quote
Ginch wrote:
Is it actually touching the crank though? They normally have a spacer between the crank web and the conrod on both sides.
It has the spacers



And it does rub

15433708378952383870384728519360.jpg

1543370914430124334571994201370.jpg

Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and new to 2018, '66 Blue Badge Smallframe
Joined: 30 Nov 2011
Posts: 6499
Location: Victoria, Australia
Tue Nov 27, 2018 6:12 pm quote
Is that one you put together yourself? Obviously it shouldn't be rubbing.
Enthusiast
2003 Derbi bullet 2 stroke
Joined: 09 Jul 2018
Posts: 73
Location: Texas
Tue Nov 27, 2018 6:14 pm quote
Ginch wrote:
Is that one you put together yourself? Obviously it shouldn't be rubbing.
No, I hadn't tooken it apart yet because I need to figure out the con rod situation and now this rubbing
Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and new to 2018, '66 Blue Badge Smallframe
Joined: 30 Nov 2011
Posts: 6499
Location: Victoria, Australia
Tue Nov 27, 2018 7:28 pm quote
So if it's new crank, send it back!
Enthusiast
2003 Derbi bullet 2 stroke
Joined: 09 Jul 2018
Posts: 73
Location: Texas
Tue Nov 27, 2018 7:51 pm quote
Ginch wrote:
So if it's new crank, send it back!
Not a new 1 unfortunately. So what do you think it could be? Im thinking big end bearing for no particular reason
Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and new to 2018, '66 Blue Badge Smallframe
Joined: 30 Nov 2011
Posts: 6499
Location: Victoria, Australia
Tue Nov 27, 2018 9:26 pm quote
If it's the big end, there will be movement up and down felt at the conrod. The traditional way to test is put your middle finger through the little end of the conrod, make a fist and let the crank hang. Then hit your hand with the other hand. If there is movement in there, apparently you should hear a ringing sound from the crank.
Enthusiast
2003 Derbi bullet 2 stroke
Joined: 09 Jul 2018
Posts: 73
Location: Texas
Wed Nov 28, 2018 6:43 am quote
Ginch wrote:
If it's the big end, there will be movement up and down felt at the conrod. The traditional way to test is put your middle finger through the little end of the conrod, make a fist and let the crank hang. Then hit your hand with the other hand. If there is movement in there, apparently you should hear a ringing sound from the crank.
Ok I'll try that
Enthusiast
2003 Derbi bullet 2 stroke
Joined: 09 Jul 2018
Posts: 73
Location: Texas
Wed Nov 28, 2018 12:02 pm quote
Ginch wrote:
If it's the big end, there will be movement up and down felt at the conrod. The traditional way to test is put your middle finger through the little end of the conrod, make a fist and let the crank hang. Then hit your hand with the other hand. If there is movement in there, apparently you should hear a ringing sound from the crank.
ok i did that and i do hear a ringing sound. there is alittle bit of up and down so i think it is the bottom end bearing
Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and new to 2018, '66 Blue Badge Smallframe
Joined: 30 Nov 2011
Posts: 6499
Location: Victoria, Australia
Wed Nov 28, 2018 10:30 pm quote
Well there you go... time for a new one!
Member
various handlebars and smallframes
Joined: 10 Jul 2012
Posts: 27
Location: Chattanooga Tn
Thu Nov 29, 2018 5:41 pm quote
I hope Im not intruding but I rebuild a fair amount of crankshafts for single and multicylinder two strokes and four strokes and may be able to offer some insight:
On a factory Oem crankshaft I have never seen one that would rub the webs if an axial load (side to side) was put on the rod. Not to say that it doesnt exist. I have just not seen it.

The best way to know is to measure the gap between the big end and the web. Many are around .02". If that spec is close and you still have over a mm or 2 side to side movement, you probably have radial (up and down) play as well.
Hope this helps

Joe
Enthusiast
2003 Derbi bullet 2 stroke
Joined: 09 Jul 2018
Posts: 73
Location: Texas
Thu Nov 29, 2018 7:08 pm quote
saintscycleworks wrote:
I hope Im not intruding but I rebuild a fair amount of crankshafts for single and multicylinder two strokes and four strokes and may be able to offer some insight:
On a factory Oem crankshaft I have never seen one that would rub the webs if an axial load (side to side) was put on the rod. Not to say that it doesnt exist. I have just not seen it.

The best way to know is to measure the gap between the big end and the web. Many are around .02". If that spec is close and you still have over a mm or 2 side to side movement, you probably have radial (up and down) play as well.
Hope this helps

Joe
I have about 0.02mm the big end. It does look like the crank has been rebuild before. I do have like a tiny tiny bit of up and down movement.
Molto Verboso
Joined: 26 Oct 2015
Posts: 1132

Thu Nov 29, 2018 7:34 pm quote
I have a crank from a TS1 240 with the con rod that just barely rubs on the webs. There’s a reason why that crank now gathers dust on the shelf and is not still in the engine.
Member
various handlebars and smallframes
Joined: 10 Jul 2012
Posts: 27
Location: Chattanooga Tn
Fri Nov 30, 2018 5:52 am quote
Sounds like you need a rebuild.
Enthusiast
2003 Derbi bullet 2 stroke
Joined: 09 Jul 2018
Posts: 73
Location: Texas
Fri Nov 30, 2018 6:54 am quote
saintscycleworks wrote:
Sounds like you need a rebuild.
Who's someone who does good rebuilds? I obviously can't do it myself
Hooked
Joined: 06 Dec 2011
Posts: 431
Location: twincities
Fri Nov 30, 2018 5:18 pm quote
saintscycleworks would be the first one I'd ask.
Enthusiast
2003 Derbi bullet 2 stroke
Joined: 09 Jul 2018
Posts: 73
Location: Texas
Fri Nov 30, 2018 5:21 pm quote
matty5 wrote:
saintscycleworks would be the first one I'd ask.
For the crank rebuild? I didn't know he did that for peeps
Hooked
Joined: 06 Dec 2011
Posts: 431
Location: twincities
Enthusiast
2003 Derbi bullet 2 stroke
Joined: 09 Jul 2018
Posts: 73
Location: Texas
Fri Nov 30, 2018 6:11 pm quote
Awesome. I'll probably be rebuilding my crank when I'm ready
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