Con rod and cap alignment

K

KennyBradley

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Jul 28, 2005
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Hi,<br /><br />I'm trying to rebuild my 1986 Evinrude 70. I'm having problems aligning the con rod caps. I seem to be able to get one on each side to line up but can't get any more than that.<br /><br />I've made up a tool consisting of two small v-blocks which I clamp across the chamfered edges but it doesn't seem to help much.<br /><br />I've tried gently tightening the bolts and tapping the cap to get it aligned but they don't seem to want to move.<br /><br />Maybe I'm being too carefull. I'm trying to get them so I can run a pencil across the break without feeling anything?<br /><br />How perfect does it have to be before bearing failure is likely?<br /><br />Any tips or advice would be much appriciated.<br /><br />Cheers Kenny
 
S

Solittle

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Apr 28, 2002
Messages
7,518
Re: Con rod and cap alignment

Did you keep the caps with the rods that they came off of when you disassembled the engine? My guess is that you got them mixed-up. If so try to move one to another to see if you can get them back to the rod they came from. They also must face the same way on reassembly as they did when they were removed. I am not the expert on this but from all the posts I have seen here that they must be kept together and a perfect fit is a must.<br /><br />Do you have the shop manual?
 
G

G DANE

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Nov 24, 2001
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2,476
Re: Con rod and cap alignment

Pay more attention to the ground corners than the sides. So does the original tool. Be sure they wernt mixed up or turned, like s.l. says. I always did like you told you do, never had problems.
 
G

G DANE

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2,476
Re: Con rod and cap alignment

Heres what I did earlyer. If you feel uncomfortable, assemble one without bearing/cranck and feel the internal line. There should be none. Compare to outher. You will see, the corners are ground last.
 
K

KennyBradley

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Jul 28, 2005
Messages
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Re: Con rod and cap alignment

Hi Guys,<br /><br />Thanks for all the replys.<br /><br />I can confirm:<br />All the caps are fitted to the correct rods.<br />All the caps are fitted the correct way around.<br />I have been trying to align the chamfered corners not the flat sides.<br /><br />I suppose I will just have to keep trying. I wasn't sure what level of perfection was required but it sounds like it has to be absolutley spot on. I am able to get one corner on each side so I can feel nothing at all with a pencil but the other 2 have a small step I can JUST feel with the pencil.<br /><br />If I remove one con rod can I pressume it should not be possible to feel any join on the inside at all?<br /><br />My manual says you should align 3 corners. Is this correct or is it possible to get all 4 perfect?<br /><br />Thanks again for your help.<br /><br />Cheers Kenny
 
OBJ

OBJ

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Dec 27, 2002
Messages
10,161
Re: Con rod and cap alignment

Kenny....there is the possibility that during the original assembly and torquing that the edges have "squished" out. What you may be feeling with the pencil are these slightly protruding edges. It's common. Follow SL and GD's advice. You should be fine.
 
R

rodbolt

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Sep 1, 2003
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20,066
Re: Con rod and cap alignment

and once its assembled and torqued use a small pick to insure the bearing will rotate smoothly on the journal and rod bore.
 
K

KennyBradley

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Jul 28, 2005
Messages
32
Re: Con rod and cap alignment

Thanks again for all the replys.<br /><br />I've had another go tonight. I've foung if I just tighten the bolts finger tight I can get reasonable alignment. But, no matter how carefully I tighten them it seems to pull them out of alignment again.<br /><br />I'm realy frustrated now.<br /><br />Kenny
 
G

grotmeister

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Sep 25, 2005
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Re: Con rod and cap alignment

Hi kenny, I'm reading this thread with great interest as I'm about to do the same thing as you! All I can say is stick with it and stay in here coz the experts are here to help you. I'm lookin forward to the time when I can hopefully put something back into the system. good luck!<br />chris
 
K

KennyBradley

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Jul 28, 2005
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Re: Con rod and cap alignment

Ok,<br /><br />So my engine is just about ready. I got my alignment so I was reasonably happy but now I'm ready to run her up I getting a bit of doupt creeping in.<br /><br />After alignment everything turned over very smoothly, the bearing could be rotated freely and as the crankshaft was turned you could see the bearing turning freely between the rod and the crank.<br /><br />Just out of interest does anyone have any experience of rod bearings failing due to misaligment? Are they likely to go very quickly or over a prolonged period?<br /><br />Kenny
 
OBJ

OBJ

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Re: Con rod and cap alignment

The only one I've seen is when a guy brought his engine in after one month of operation after HE rebuilt it. I took it apart and found he did not keep the rod caps with the right rod. I don't understand to this day why it ran so long....... :eek: <br /><br />I think you will be fine Ken. Break it in easy and you will be happy with your job.<br /><br />Good Luck!
 
D

Dhadley

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Feb 4, 2001
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16,978
Re: Con rod and cap alignment

Think about this -- we don't really care if the outside is lined up or not. It's the inside that counts. The outside is our guide. In a perfect world that cap will not distort and will line up inside and out. Or not. <br /><br />99.5% of the time they will line up inside and out. We've seen some that wont line up outside perfectly but are inside. Ans vise versa. The bottom line is that if you kept the right caps on the right rods and the little dots lined up and the rollers roll free, it's most likely OK.<br /><br />Like I say -- 99.5% of the time they line up and you cannot feel a line. Even with a pencil.
 
K

KennyBradley

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Jul 28, 2005
Messages
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Re: Con rod and cap alignment

Thanks for the replys and reassurances guys. I'll hopefully get the chance for a terst run in the next couple of weeks.<br /><br />This is the first engine I've seen with this set up. It strikes me as very strange that a roller bearing under the hassh condition inside a 2-stroke engine can function reliably with a join in the outer race no matter how well it is aligned.<br /><br />It obviously works though!!
 
D

Dhadley

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Feb 4, 2001
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16,978
Re: Con rod and cap alignment

Those are what they call "cracked" rods. The caps are actually sheared off. Nothing fits back together as good as a broken piece. Most of the time you cannot even find the seam.
 
K

KennyBradley

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Jul 28, 2005
Messages
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Re: Con rod and cap alignment

Hi guys,

Just wanted to say now our boating season is over that the engine has run fine and so far there have been no indications of rod bearing problems.

Hopefully I'll get many more seasons out of her.

Thanks for all the advice above.

Cheers Kenny
 
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