What's the difference?

[bearsfolks]

I recently had a top-end job done on my 83 R80RT (at 63,000 miles) and was told the heads needed to be retorqued after 600 miles. I was unable to get back to the shop, so, at about 800 miles I removed the valve covers and checked the torque. It would barely register on my torque wrench, probabaly 15 ft/lb or less. I then torqued the bolts in the proper sequence to 29 ft/lb and buttoned up the motor. I have ridden the bike now about 500 more miles, and had reason to visit my dealer's service department on another issue. I asked about valve clearance and mentioned the very low torque reading when I retorqued the heads. I was told , in rude terms, that since I didn't back off the studs 1/4 turn before tightening them again I probably had ruined the motor. No studs broke or pulled loose, and since the initial reading was so low I wondered about the need to back off the studs. What's the reason to back off the studs when they initially were so loose? The bike runs fine.

[nealart]

As long as each one started at less torque than what you ended up with, and moving smoothly, I should think you did just fine.

I am not an engineer, but I would guess the back-off is a safety measure to be sure you are not over torquing and also to be sure the nut is moving smoothly and not stuck which might give a faulty reading.

[jforgo]

I am not an engineer either. But the reason to back them off is to "zero" the nuts, so there is an even starting point , to which then the correct torques and sequences are applied. If you use a starting point where existing torques are uneven and/or excessive, the risk of warpage and breakage is there.

Interestingly, since you did it after top end job, when things settle and loosen, you started closer to zero, if not even, than normal. So I think your specific scenario is the least likely to cause breakage or warpage.

BTW, did you need new pistons? I wonder what current costs were, and for what jobs. Did you get the unleaded conversion?

[bearsfolks]

I didn't need new pistons, the heads were worked with new valves and seats, new piston pins, rings and rod bearings. I also had new tires installed with new tubes and had all the wheel bearings and seals replaced, and had the 500 W alternator done. $2600 or thereabouts.

[jforgo]

Wow! Now you have to keep it!

[20774]

The nuts should be backed off maybe 1/8 to 1/4 of a turn and then retorqued. The idea is to measure the "running" torque...it's really a measurement of the sliding friction/tension in the bolt. It's not good to back off to zero torque because now the head is not held evently amongst the 6 nuts/bolts. The slight reduction of 1/8-1/4 turn is not enough to create a serious difference between the remaining nuts.

That said, I tend to only put the torque wrench on and see if I can get to the specific number without the nut turning. If it doesn't turn, I consider it good. Since I was the last one to do the torquing, I'm just going to check to be sure it hasn't loosened...probably not much chance that it's tightened by itself! If it was an unknown motor, I might back off slightly and get the running torque reading.

BTW...I've heard that the number to use is more like 25-26 ft-lbs. There might be some published differences, but there was a spate of pulled studs. The 29 value seems too high...not really necessary to be that him AFAIK.

[Bill Burke]

BTW...I've heard that the number to use is more like 25-26 ft-lbs. There might be some published differences, but there was a spate of pulled studs. The 29 value seems too high...not really necessary to be that him AFAIK.
Kurt's right. 25 foot pounds is the presently-accepted target by most airhead gurus. 29 risks pulling the studs out of the case. And if you read your torque wrench instruction booklet carefully, you'll find that one should "never" torque a nut that's in repose at its torqued value. In other words, back it off a tad as described above, then smoothly bring to target torque.

[krehmkej]

My guess is that the main issue here is the shop now has an "out" so as to not have to stand behind their work.

[Jeff488]

When I had the head work done on my airhead, I read and was told that after the initial tightening of the head bolts, to re torque them after several heat cycles. I did this about 3 times and each time I re-torqued them(except the last), I found that the valves had closed up a fair amount.

[crazydrummerdude]

I didn't need new pistons, the heads were worked with new valves and seats, new piston pins, rings and rod bearings. I also had new tires installed with new tubes and had all the wheel bearings and seals replaced, and had the 500 W alternator done. $2600 or thereabouts.

Your bike's doomed. I'll take it off your hands.







(So far, I agree with what the others have said.)

[bearsfolks]

Thanks for the responses. I got the 29 ft/lb from a Clymer's Manual as the high range. Valves were tight and I adjusted them today. I got my good idle back, so I'm happy. I've had the bike 15 years and I guess I'll keep it a while longer.

[beemerguru]

There's also a reason for the 3 stage torque process you should have seen in all the manuals..

By backing each nut a 1/4 turn, all those new parts get to settle a bit. So when you do the first round at 10 lbs, you check the vertical movement of the rocker arms. Any slack will just cause noise and not effect the operation of the engine. So you make sure to remove the slack for a quiet valve train.

Then the next 2 torque sequences are done as sssllllloooowwwwlllllyyy as you can. Don't just jerk the torque wrench till it clicks or see how fast you can get the needle to 19, then 25 lbs.

Do it evenly and slowly to let the metal parts bend - they do that - and conform to their final position.

And the reason for the 25 lbs final number is just what someone mentioned earlier,,so you don't pull a stud (s). 25 is a good number..and given that most people never send their torque wrenches in for recalibration, a safe number.

The last thing you want to do it pull a stud.. a real PITA to take it all apart to install a heli coil or insert. And when you do the second time because you have an early 80's engine or think torqueing is a substitute for lifting weights...go find a late model short block and/or a good torque wrench.

[beemerguru]

ps: your '83 is more suseptable to pulled studs because the metalurgy was changed for those early year engine3..softer.

IF you can find a mechanic who's been doing this for the last 30 years, they might have a copy of the BMW bulletin issued at the time mandating that the final torque number was 25 lbs .PERIOD..not 26 or 27.

Seems there was a rash of pulled studs from using the published 29 lb number.

Metalurgy was later changed - duh.

[beemerguru]

And while you were having all this work done,,,you did spend the extra $100 or so to have the moving parts balanced? Pistons, rods and wrist pins?

[DennisDarrow]

Just to find out what the "experts" think. I have always treated the head bolts and nut assemblies as indiviual entities. Meaning, I dont loosen ALL of them and then torque them using the proper pattern. I do each one individually.

The thinking, by the ancient mechs that I learned this from, is that it does allow for reseating of surfaces and mechanisms; but doesnt allow the whole thing to shift. Perhaps the "ancients" were incorrect and would like some modern day thinking on this as no one mentions treating each bolt/nut individually and write instructions as if all are to be loosened and then retorqued.

A bit of clarification would be great..........thanks........Dennis

[bearsfolks]

Thanks you for all your encouragement and criticism. I went back and re-torqued the heads exactly as described in the Clymer Manual to 25 ft/lb. Nothing broke or backed out so now I have nothing to worry about. Right? Got the old , sweet idle back and so I'm happy as a clam.

[orbitangel]

...I was told , in rude terms, that since I didn't back off the studs 1/4 turn before tightening them again I probably had ruined the motor...

What a load of CRAP! I resent so-called "Service Providers" who promote attitudes like that. :banghead

[PHMarvin]

Hi, Bearsfolks,
You retorqued the nuts to 25 ft/lb. Fine. As long as none of the studs had pulled out at the 29 ft/lb, you should be fine. I would check (and maybe retorque, again to 25 ft/lb) the next time you do the valve clearances - maybe in another 2.5-5k miles. From then, you should be fine (for torque) for many, many miles.