Topic: connector rods-how tight should the bolts be?

[holajeffe]

I replaced my connector rod bearings and I am wondering how tight I should make the bolts when putting the rods back on the crank.
I initially tightened them way down but then the rods had a what seemed to be far too much resistance...when I loosen them a bit they spin far better, but I def don't want to lose a nut in my crank case.

thanks!

Jeff

[dave500]

you have the wrong size bearings,they shouldnt lock up or go tight,if its a 500/550 you want 14-16 ft/lbs,,download the manual from this site.

[KingCustomCycles.com]

Those bolts you just overtightened are now junk.  Rod bolts are one time torque only as they stretch during tightening to provide an elastic "hold" on the bearing even during various loads and heating and cooling cycles.  They are what is refered to as "critical internal engine parts"

[dave500]

i use them over and over,if its a race engine replace them,,but if they have been over torqued replace them.

[holajeffe]

It's a 750.  according to my manual I needed green bearings, so that's what I got.  When I torqued down on them (12 ft pounds or so) hard they still spun but they didn't seem super loose.  I went back and put in the bearings I was replacing just to see what the difference was and they felt the same way.  So I guess I am just wondering how loose the connector rods should feel.  Should they easily drop went I let go?

sounds like it's the rod bolts like King Custom says.  I hadn't even thought to replace them as well.

[KingCustomCycles.com]

You can take a measurement of the OD on the crankshaft and an ID of the Con rod bearing (assembled and tightened) and determine a clearance.  I believe that spec is in the manual.  Yes, they should be free enough to drop with gravity.  Side to side (end clearance) is rather noticeable. 

[MRieck]

Did you lube the bearings? Tighten the bolts in 3 stages (and I don't mean tighten 1 bolt in 3 stages and then the other).

[dave500]

if you had green bearings before ,green should be ok now,,they should drop down,,,as asked were they oiled,,plasti guage is an option,,if you only went to stock torque specs those bolts will be ok,these are over engineered engines and heavy in that respect,as per mrieck  "square up" as you tighten the bolts down.

[holajeffe]

"Tighten the bolts in 3 stages (and I don't mean tighten 1 bolt in 3 stages and then the other)."  ha ha!

yep, I did lube the bearings, but I didn't do the tightening in 3 stages.

a little background:

this bike is from 1971 and there are def signs that someone at some point did this before me, maybe the connector rod bolts just couldn't take any more.

I've owned old bikes for years (my main ride is a 1971 BMW 75/5) and have done all sorts of tinkering with them, but never attempted a full on tear down before.  When I got this bike it was a total beater, but ran great.  I did all sorts of fun things to it, shortened the frame in the back, made a new seat, bought a 1920's John Deere gas tank and used it as my oil tank...I finally got it all together in July and on my very first ride (probably the hottest day of the summer, 105 degrees here in Philadelphia) I seized the engine.  The return oil line was majorly kinked (I had moved some things around the day before and made a mental note to check the lines and totally forgot.) and all the oil had just stayed in the bike.

I tore the engine apart and saw that one of the connector rod bearings had totally fused to the crank. 

Well, I did buy this bike to learn more about engines and how bikes run-I am getting some good experience I can tell you that!

I've included a picture of my bike right before it stopped working.  well, 15 minutes before!

[dave500]

ok,,if one of the bearings had fused(siezed)to the crank maybe the po(previous owner)has used the wrong ones,now your just going to repeat his mistake maybe?you need to size(not sieze) them up and figure out what ones you need,,if the crank is scored you need to have a good look at it,,itll tear any new bearing to bits if you just shove a new bearing in there and youll repeat all this again.

[wrenchmuch]

As Dave said check the crank , but that kind of damage almost always damages the journal . Did the bearing spin inside the rod ?

[holajeffe]

when this first happened I talked to a local old timer up the road a bit who used to be a pro racer for Honda back in the early 60's through early 70's, he repairs old bikes in his retirement-

He told me that since I'm not racing the thing just to make sure the journals aren't badly gouged (which they are not) polish it down a bit light steel wool and just think of any small grooves that I can't see as extra places oil can flow. 

The bearing were really fused to the journals and no they wouldn't spin at all.  I was able to peel them off  and thought about going the new crankshaft route but after getting the bits off of the journal they look and feel pretty dang smooth.  I know "pretty dang smooth" isn't really very scientific and all, but still....

by the way, the stories this guy tells of the old days of racing are pretty steller....His bike collection is pretty dang sweet.

anyway, is his advice just crazy talk?

[KingCustomCycles.com]

I had a bearing seize to the crank and the engine ran quite a bit after that because the back of the bearing was so polished from turning inside the rod I thought it was the journal.  When I went to reassemble with new bearings, nothing made sense with the measurements and I finally realized what had happened.  That bearing was freakin welded to the crank.

[RRRToolSolutions]

What ever happened to using Plasti-gauges? You know, those little strips that every parts counter sells cheap and is designed for clearance measurements?

Regards, Gordon

[MCRider]

What ever happened to using Plasti-gauges? You know, those little strips that every parts counter sells cheap and is designed for clearance measurements?

Regards, Gordon

Many of us have done so just recently even. But with a seizure, I'd say polishing the journal and having it miced for roundness, which is a weakness of Plastigauge, is probably a good idea.

[MRieck]

The rod caps are on the right rods....right. You will definitely have binding problems if the caps are on the wrong rod and/or reversed.

[holajeffe]

well, I think I may have solved the problem-I thought I had been keeping the caps with the correct rods, but somewhere along the line it looks like I reversed two of them.  I'm not sure if I did this or if the guy before me had, but the def weren't lining up correctly and now they are. 

But also when I re-tightened the bolts I made sure to tighten them down in 3 stages and that made a difference, too.  I also think I did a better job of lubing the bearings. 

so maybe it was one of those things or all of them combined, but they are definitely far smoother than when I first put them back on.

I just got done getting the case back together and putting the pistons back on-getting the 3 chains back over the crank was a real pain.  I did it per the manual's instructions but I wonder how they did it in the assembly line.  Seems way tricky. 

 Do I need to lube the pistons, too?  Or is the oil circulating around enough?

thanks for all of your help, guys.  You are awesome!

[dave500]

lube everything!