Topic: Cb500 Yoshimura Rod Bolt torque setting

[pangloss]

Have opened up my CB500 engine with view to freshening it up and putting back on road.  Plastiguaged all the big ends and mains with ALL bearings being 2.5 thou clearance using a nominal torque down of 15 ft/lb   BUT   what would be the CORRECT torque value for these rod bolts...??   I fitted them in 1977 and  have No documentation Or memory of the correct torque.... Any ideas ?  Thanks .Jeremy

[MRieck]

What size are the bolts? I'd imagine about 22 or 23 ft lbs. Do you have a stretch gauge? I'd go for .005 of stretch in an aluminum rod.

[MRieck]

Also....what are you using for bolt lube?

[Dresda500]

I have the original sheet from Yosh with my rods and no torque given, but your bearing clearance is on the loose side. As mentioned in the sheet, these rods are not stock length, but longer.

[Dresda500]

I wouldn’t believe it if I didn’t have it on the bench….bolts are 5/16-24….i took a set out of the wax and for curiosity sake put a torque wrench on for both removing and to just break loose tightening. Threads were dry…or are now after 40+ years on the shelf…but have been encapsulated in wax…25ftlbs to break loose, 45 ftlbs to tighten(just breaking the set)

[HondaMan]

Just a refernce (FWIW) from my roadracing days (from the CB750 engines): we set the rod and crank clearances at 0.0010"-0.0012" after break-in running to 8500 RPM (most were 300-800 miles by then). We found that after the season they had pressed out to 0.0012"-0.0015". We also used 20w50 oils none used synthetics then.

[Dresda500]

Good info Hondaman. For some reference, here are the recommendations from Carrillo for both steel and aluminum rods. Notice they advise a much larger clearance on the bearing. They don't specify what rod journal diameter that is...so likely a generalization for larger diameters than we are talking here.  I think I'd lean towards the tighter clearances mentioned on the Yosh sheet and by Hondaman for these particular rods. Speaking generally I've often gone by the general rule of 0.001 clearance per inch of journal diameter, so the 34mm CB500 rod would be appx 0.0013in....right in line with Hondaman's experience and Yosh

[MRieck]

 Steel Carrillo's like clearance towards the high end....like .0018. Those aluminum torque figures are for some hefty rod bolts....7/16 is a big bolt. The last aluminum rods I installed I ran .080 valve to piston clearance. Check what Golden Rod torque.....it should be here on the forum. I always go by bolt stretch.

[Dresda500]

Steel Carrillo's like clearance towards the high end....like .0018. Those aluminum torque figures are for some hefty rod bolts....7/16 is a big bolt. The last aluminum rods I installed I ran .080 valve to piston clearance. Check what Golden Rod torque.....it should be here on the forum. I always go by bolt stretch.

Agree Mike, the steel rod page has the smaller bolts but not the aluminum. Yeah, I agree, stretch is best, but then it’s really best to know the material quality. If you try to stretch a high strength bolt as much as a medium strength, with out knowing, you could have a bad day real quick, especially with aluminum threads. Probably wise to do a test on the bolts in a test fixture to see stretch vs torque, or replace with known bolt.

[Tracksnblades1]

Pangloss,

You can always warm your rods up to 200*f with the bolts and bearing installed and measure your bearing diameter.
Most aluminum rods bores are intentionally sized on the skinny side because they expand at a quicker rate than their steel counterparts.

I’d measure your side clearance/rod thickness at near running temp for just the rod. And like already mentioned, Aluminum rods get longer with temperature, so the additional piston to valve clearance is always recommended.

With .0025 clearance cold/rod you’ll probably be running straight 50 or 70weight at operating temps…..I’m sure with steel rods and that clearance you could hear them on no oil pressure start up after it sits for a while.  I haven’t heard of clearances on that small of a journal like that unless running some good fuel and boost….With aluminum rods the clearances only get bigger with temp so I prefer the minimum side of the clearances compared to the looser ones. However the tight clearances are less forgiving when things don’t stay straight, square, and true to the world..

[Dresda500]

Pangloss,

You can always warm your rods up to 200*f with the bolts and bearing installed and measure your bearing diameter.
Most aluminum rods bores are intentionally sized on the skinny side because they expand at a quicker rate than their steel counterparts.

I’d measure your side clearance/rod thickness at near running temp for just the rod. And like already mentioned, Aluminum rods get longer with temperature, so the additional piston to valve clearance is always recommended.

With .0025 clearance cold/rod you’ll probably be running straight 50 or 70weight at operating temps…..I’m sure with steel rods and that clearance you could hear them on no oil pressure start up after it sits for a while.  I haven’t heard of clearances on that small of a journal like that unless running some good fuel and boost….With aluminum rods the clearances only get bigger with temp so I prefer the minimum side of the clearances compared to the looser ones. However the tight clearances are less forgiving when things don’t stay straight, square, and true to the world..

Good info! I don’t have experience with this small journal in an aluminum rod, only big stuff we use on our 1000+hp motors out at Bonneville. I’m definitely not running gear oil so think I’ll go towards the tight side as well and yes do some R&D in the shop with some heat in the rods.

And funny enough, I thought to pull out the original Yoshimura sheet…and sure enough, if you unfold it…there’s your torque spec…😂

[MRieck]

What size are the bolts? I'd imagine about 22 or 23 ft lbs. Do you have a stretch gauge? I'd go for .005 of stretch in an aluminum rod.

Do I win a prize???

[Tracksnblades1]

And funny enough, I thought to pull out the original Yoshimura sheet…and sure enough, if you unfold it…there’s your torque spec…😂

That’ll remove all doubts and put the worry wort’s mind at ease and allow them to move on to the next real concern,
“Fatigue “.

With aluminum rods it’s not “IF”….  Replace them at the recommended interval or when your rod measurements “indicate” it’s needed…

[pangloss]

Wow !  Thanks very much for these replys .. Much appreciated.

Mike, your on the money with your torque .

And Dresda !!  Actual documentation  !!!!!

The one smart thing I did before dissassembling the rods from their 40 something year slumber was mark where they were before undoing.  So as a check i retorqued them (dry) and got around 24 foot pound average so I'll re plastiguage at that torque.

Keep in mind this engine is going back on the road pretty much as a "restored original "  cb500 show pony. I have the original rods but lost all the shells.! so if the Yoshi rod bearing clearances are OK I'll save quite a few $$ A  sourcing new shells. Assuming they are even available.

Cheers and Thanks   Jeremy

[Tracksnblades1]

Wow !  Thanks very much for these replys .. Much appreciated.

Mike, your on the money with your torque .

And Dresda !!  Actual documentation  !!!!!

The one smart thing I did before dissassembling the rods from their 40 something year slumber was mark where they were before undoing.  So as a check i retorqued them (dry) and got around 24 foot pound average so I'll re plastiguage at that torque.

Keep in mind this engine is going back on the road pretty much as a "restored original "  cb500 show pony. I have the original rods but lost all the shells.! so if the Yoshi rod bearing clearances are OK I'll save quite a few $$ A  sourcing new shells. Assuming they are even available.

Cheers and Thanks   Jeremy

How did you get the .0025 plastic gage measurement without the shells?

Plastic gage will not give you journal taper or run out and it’s only should be used with the shell and journal dry..

[pangloss]

Lost the shells from the original steel rods which were swapped out for the current Yoshi rods 40 odd yrs ago.

[Tracksnblades1]

Lost the shells from the original steel rods which were swapped out for the current Yoshi rods 40 odd yrs ago.

I see. Are the original Honda bearings different from the yoshimura’s..? Are your yoshi’s pinned..?

Dirt guys won’t run aluminum. Drag guys don’t put many passes on them above 8,000 before tossing them for new ones..

They may live in a trailer Queen though. I know they don’t like no load rpm’s…

[newday777]

Lost the shells from the original steel rods which were swapped out for the current Yoshi rods 40 odd yrs ago.

I see. Are the original Honda bearings different from the yoshimura’s..? Are your yoshi’s pinned..?

Dirt guys won’t run aluminum. Drag guys don’t put many passes on them above 8,000 before tossing them for new ones..

They may live in a trailer Queen though. I know they don’t like no load rpm’s…

No load RPMs???

[Tracksnblades1]

Lost the shells from the original steel rods which were swapped out for the current Yoshi rods 40 odd yrs ago.

I see. Are the original Honda bearings different from the yoshimura’s..? Are your yoshi’s pinned..?

Dirt guys won’t run aluminum. Drag guys don’t put many passes on them above 8,000 before tossing them for new ones..

They may live in a trailer Queen though. I know they don’t like no load rpm’s…

No load RPMs???

[Dresda500]

My Yosh rods have pins. So I guess, one had to drill the Honda bearings for the pins.

[Dresda500]

What size are the bolts? I'd imagine about 22 or 23 ft lbs. Do you have a stretch gauge? I'd go for .005 of stretch in an aluminum rod.

Do I win a prize???

Mike, swing by and first beer is on me!!!