Topic: CB750 890cc Engine build [Codename: Rattlesnake]

[michrobi]

Got the cases put together, assembled the rotor, gave it a little turn, but no turn. Gave it some more torque, nothin...

At 20 lbs. on the mains the crank is clamped. At about 17.5 lbs. it turns normally. I plastigauged those bearings dry with stock main bolts at 16.5 lbs. and got .0015" across the board. Now it seems like the black bearings are too big.

That pretty much blows.

[Jerry Rxman Griffin aka MuthaF'er]

Yeah, that really bites!

I matched up the original letter readings then I took my digital calipers to my crank and used the chart. Both said green so I kept my fingers crossed. Torqued it to 22lb with Plastigauge. I got your readings, .0015, all across too. I figured that's at the top end of the range so it should be OK. Spins freely. I'm only going to have a few days to work on it the next month or so. You'll be done by the time I get started again! You haven't missed something else like a binding cam chain, tranny, etc have you??

 

[MCRider]

Wow M & J. I wouldn't have thought the extra torque would continue clamping smaller. Just tighter. Guess we're learning. I'm looking to button mine up soon.

I did the stock bolts at 16.5 got .0015 with 3 greens and 2 browns. I'll be putting in the HD studs and clamping a little tighter for final assembly. Stand by...

[a700guy]

When we build some heads, exceeding the specified torque would not only bind the cam in the machined carrier but also completely reduce the lash (bucket and shim).

I would be curious if one was to torque an empty set of cases and measure the mainbearing bores with a boregauge if it is even still round at the exceeded values.

I have seen many many cams and carriers smoked from not using a torque wrench, which always means they exceeded specified torque 14nm usually 18+.

as little as 16nm has been seen to distort the bore enough to feel it by hand, and this is with modern f1 quality alloys and they have centering dowels at every bolt hole also.

Just my 2 cents

[MRieck]

When we build some heads, exceeding the specified torque would not only bind the cam in the machined carrier but also completely reduce the lash (bucket and shim).

I would be curious if one was to torque an empty set of cases and measure the mainbearing bores with a boregauge if it is even still round at the exceeded values.

I have seen many many cams and carriers smoked from not using a torque wrench, which always means they exceeded specified torque 14nm usually 18+.

as little as 16nm has been seen to distort the bore enough to feel it by hand, and this is with modern f1 quality alloys and they have centering dowels at every bolt hole also.

Just my 2 cents

Honestly...it's Chicken sh$t here with torque values. Clamping values are so low. We are talking 6 and 8mm fasteners.

[Jerry Rxman Griffin aka MuthaF'er]

It'd be kinda dumb to exceed the specified torque values. I'd worry more about breaking the bolts or stripping the threads. I was concerned using 10lb on the 6mm case bolts.

Keep in mind here that the torque value for the heavy duty studs is 20-22lb.

Does anyone have a value for the 6mm bolts? The manual just says "torque them"

[MCRider]

Jerry:
Scroll down for generic torque recommendations.

http://www.salocal.com/sohc/tech/torquetable.htm

[MRieck]

It'd be kinda dumb to exceed the specified torque values. I'd worry more about breaking the bolts or stripping the threads. I was concerned using 10lb on the 6mm case bolts.

Keep in mind here that the torque value for the heavy duty studs is 20-22lb.

Does anyone have a value for the 6mm bolts? The manual just says "torque them"

By feel Jerry. Trust me.

[Jerry Rxman Griffin aka MuthaF'er]

Know what you mean Mike. I worked a couple up toward 10 but quit just shy when it just wasn't feeling right! I've felt them strip and snap. That feels worse. 

[BLUE71TURBO]

  Ya Jerry, there's nothing worse than stripping and then snapping your nut on yer bolt !!!         

[a700guy]

My bad, I thought you guys were saying that you were torquing tighter than oem values because you were using studs.

[a700guy]

It'd be kinda dumb to exceed the specified torque values. I'd worry more about breaking the bolts or stripping the threads. I was concerned using 10lb on the 6mm case bolts.

Keep in mind here that the torque value for the heavy duty studs is 20-22lb.

Does anyone have a value for the 6mm bolts? The manual just says "torque them"

Specified torque is 16-18ft lbs in the manual, 22 is 4 ft-lbs over that. In my experiance torquing something over the range is was machined at usually leads to an un-round hole was all I meant.

I have a bore gauge, after I get my studs and all parts clean I will measure them at both settings and report back, it may be a while though.

[michrobi]

Even at 17.5 lbs. it's tighter than it should be, and that's within Honda spec range. I'm pretty sure I have too big of bearings in there. Starting to wonder if plastigauge isn't a bunch of BS. I have yet to hear of anyone getting a reading other than .0015 with any bearing.

[voxonda]

We ruined a very nice, lightened, crank by using plastigauge. Never ever use it again. If crank has not been regrinded on the mains, it's almost always the Green bearings. We used the Black also back then. Now I always check by just measuring and compare with the Honda spec's. Never had any problems, so far, again.

Rob

[MCRider]

Even at 17.5 lbs. it's tighter than it should be, and that's within Honda spec range. I'm pretty sure I have too big of bearings in there. Starting to wonder if plastigauge isn't a bunch of BS. I have yet to hear of anyone getting a reading other than .0015 with any bearing.

I started with 5 green, had to switch to 3 green 2 browns to get the right readings straight across.

[voxonda]

The earlier cases have more of a mismatch of bores. The later cases are more equally bored. Just look at the codes on the cases.

[Jerry Rxman Griffin aka MuthaF'er]

Good point. 75 750F cases with all B's and 78 crank with all A's.

[754]

Maybe recheck to make sure everything is clean, and nothing is dragging.. A human hair is thicker than the clearance, and could probably prevent it from turning..

[michrobi]

I completely cleaned the journals and bearings, then re-oiled and reproduced the same result three different times. Loosening the main studs from the clamped 20 lbs. to 17.5 lbs. or below releases the crank and the motor all turns normally. New bearings are ordered and will hopefully be here in less than the two weeks my bolts took.

[a700guy]

are the bearings worn or shiny at the halve ends?

[michrobi]

Nope, every bearing is brand new. Read the thread man it aint that long yet 

[BLUE71TURBO]

 A little touchy are we ?   Sounds like the snake bit ya !      Just take yer time and be patient.  It'll work out.

[michrobi]

I know I know. I'm trying to take it in stride. Sorry for being snappy 

[a700guy]

Nope, every bearing is brand new. Read the thread man it aint that long yet 

I meant now...from turning the crank, can you see anything different from the majority of the bearing face.

Depending where has a different meaning if you can see it is all. Maybe you haven't turned it enough to shine up a spot..in which case, cool.

I was just wondering so I could possably help with why you have that particular "shiny spot"

[tweakin]

Mike, sounds like I can hold on to the carb sync tool a bit longer..... J/K

that blows, if you need a hand just let me know.