Author Topic: Cylinder head nut torgue  (Read 197 times)

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Offline bmonk

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Cylinder head nut torgue
« on: August 12, 2019, 10:49:42 PM »
I can't seem to find it in the on line manual
Does anyone know the cylinder head torque for the 1970 Yamaha Cs3-c
They are the 7 mm sleeve nuts
Thx

Online Alistair64

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Re: Cylinder head nut torgue
« Reply #1 on: August 13, 2019, 09:22:05 AM »
Good question!
I know the Supplementary Manual for the later models states it incorrectly as something like 5 lb.ft.
I've never been able to find it either, but between 12 and 15 feels about right!
The later models use 7mm studs too.
Hopefully someone can enlighten us both.
1982 Candy red RD200DX
1986 RD350F1

Online 5port

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Re: Cylinder head nut torgue
« Reply #2 on: August 13, 2019, 10:38:42 AM »
A different Yamaha manual gives 7 to 10lb ft for 7mm steel nut torque.

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Offline bmonk

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Re: Cylinder head nut torgue
« Reply #3 on: August 13, 2019, 11:22:04 AM »
Thx for the replies.
Only reference I can find is in a table that 7 mm should be 135 in/ lbs ...or 11 lbs
But it does not state it is for the head torque.
Wonder if anyone has used this spec with success .

Offline Astute Greaser

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Re: Cylinder head nut torgue
« Reply #4 on: August 13, 2019, 12:47:44 PM »
RD200A which is a variant of the same engine using M7 nuts
Yamaha Service Manual
https://www.aircooledrdclub.com/manuals/RD200A.pdf
page 11 gives you all the torque values
Cylinder head nuts
86.8 in lbs (1.0 m-kgs)
confirmed by the original owners manual that came with a new bike.
7.2 ft-lbs. (1.0 m-kgs)
I've used these figures with no problems.

The RD200B manual says
86.8 - 130.2 in lbs (1.0 - 1.5 m-kgs)

However the Haynes manual that covered the YCS3E / YCS5E and RD200 says
15 ft-lbs more than twice the lower Yamaha's figures. Experience of this published 1974 manual is its full of errors ::).

« Last Edit: August 13, 2019, 12:58:41 PM by Astute Greaser »

Offline bmonk

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Re: Cylinder head nut torgue
« Reply #5 on: August 13, 2019, 03:11:43 PM »
Thank you so much

Offline Bluehaze

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Re: Cylinder head nut torgue
« Reply #6 on: August 13, 2019, 06:17:35 PM »
Don't forget the standby method:
Tighten until it starts to strip, then back off a bit.

Online Alistair64

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Re: Cylinder head nut torgue
« Reply #7 on: August 13, 2019, 07:46:02 PM »
Don't forget the standby method:
Tighten until it starts to strip, then back off a bit.

 :D

Thinking back, I did struggle to get much over 12 lb.ft - it was achievable, but it did feel like the metal was starting to yield so I stopped (you tend to get a good feel for these things after 40 years of stripping threads!!)
I reckon 11 - 12 is a good average of all the suggestions and will feel plenty tight enough.
Would also definitely recommend re-torquing after putting, say, 50 miles on it, as I did find on my own bike that some had loosened off.
1982 Candy red RD200DX
1986 RD350F1

Offline Astute Greaser

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Re: Cylinder head nut torgue
« Reply #8 on: August 13, 2019, 11:08:01 PM »
The object of using torque is to stretch the studs creating a preload greater than that generated by max load from the engine plus expansion from temperature, thus preventing the cylinder head leaking. The studs become springs. As others have said too great a load and you'll strip threads or worse shear the studs. Too little load, head leaks.
Yamaha have established the torque figures by theory, experiment and practice.

The important points when you are torquing the Cylinder heads:
1) The threads are not corroded in good condition. Friction will be greater if not.
2) The thread on nuts and studs cleaned. Do not oil or use copper/silver grease, this will dramatically alter the stretch (preload) of the studs. Again you are changing the friction coefficient.
3) The M7 flat Washers under the nuts are not missing and the right size, don't use M8 because M7 are not readily available, ebay does them. There are no spring washers. Common sense, have you're plugs in when fitting these or you'll be sorry when they disappear. Are they between the fins, rolled away on the floor or !!!
4) Don't use thread lock
5) Progressively and sequentially load the studs in a diagonal fashion.
6) I have heard of people replacing studs with mild steel threaded rod  :o. So on M7 the tapping size is 6mm. The cross sectional area of the stud is changed plus the shear strength of the material is different (especially under high temperature). So the torque figures from the manuals will become nonsense.

People with racing bikes will do other things, that's the nature of their bikes.

I know I'm speaking to a lot of experienced people but remember not all are.

Enjoy
« Last Edit: August 13, 2019, 11:14:44 PM by Astute Greaser »

Online Alistair64

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Re: Cylinder head nut torgue
« Reply #9 on: August 14, 2019, 08:54:07 AM »
The object of using torque is to stretch the studs creating a preload greater than that generated by max load from the engine plus expansion from temperature, thus preventing the cylinder head leaking. The studs become springs. As others have said too great a load and you'll strip threads or worse shear the studs. Too little load, head leaks.
Yamaha have established the torque figures by theory, experiment and practice.

The important points when you are torquing the Cylinder heads:
1) The threads are not corroded in good condition. Friction will be greater if not.
2) The thread on nuts and studs cleaned. Do not oil or use copper/silver grease, this will dramatically alter the stretch (preload) of the studs. Again you are changing the friction coefficient.
3) The M7 flat Washers under the nuts are not missing and the right size, don't use M8 because M7 are not readily available, ebay does them. There are no spring washers. Common sense, have you're plugs in when fitting these or you'll be sorry when they disappear. Are they between the fins, rolled away on the floor or !!!
4) Don't use thread lock
5) Progressively and sequentially load the studs in a diagonal fashion.
6) I have heard of people replacing studs with mild steel threaded rod  :o. So on M7 the tapping size is 6mm. The cross sectional area of the stud is changed plus the shear strength of the material is different (especially under high temperature). So the torque figures from the manuals will become nonsense.

People with racing bikes will do other things, that's the nature of their bikes.

I know I'm speaking to a lot of experienced people but remember not all are.

Enjoy

Hi Astute
If you were to replace the studs, what would you use, as the originals are no longer available?
I'm currently in the process of a rebuild and feel I'd like to replace the studs as a matter of course - or is it more likely that the female threads within the crankcases will stretch first?

Incidentally, I take your point about Yamaha arriving at the torque figures not by chance and completely agree, but don't you think it would be helpful if they could actually publish the figure correctly?
I refer to the RD125/200DX Supplementary Manual, quoted as 5 ft-lb???
« Last Edit: August 14, 2019, 09:06:57 AM by Alistair64 »
1982 Candy red RD200DX
1986 RD350F1

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Re: Cylinder head nut torgue
« Reply #10 on: August 14, 2019, 10:37:59 AM »
So, the "Yamaha figure" is between 7 and 10 lbft depending on which reference you use.   ;)
The points about long studs being under stretch etc are correct.  If you can't get OE studs, then it becomes a question of Hobsons choice!  I have found that some of the sets for sale are nicely made and should be fine.  :)

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Offline Astute Greaser

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Re: Cylinder head nut torgue
« Reply #11 on: August 14, 2019, 04:00:40 PM »
Exactly, use the best replacements you can get hopefully from reputable supplier who will know the material grade of the original.
Like everything, if you can't get or OEM is to expensive you make a choice. These are not racing machines and thus there is a lot of leeway built in.
Its unlikely you would find anyone doing M7x1pitch threaded rod. Avoid going for stainless because you can, the strength and thermal conductance will not match the original plus you risk galling. Anyone with  a lathe or vice can make these but it is much better that the threads have been rolled rather than cut, which hopefully the pattern ones are.
If your rods are in good shape why replace them as matter of course, these are not wearing items, although they do see cyclic stresses, their only going to be fatigued if you've been to the moon or racing. Remember on the 200 engine and a lot of others you should be using the long dome (acorn) shroud nuts, meaning the threads of the rods shouldn't have been exposed to corrosion in normal conditions. Damage is more likely due to over tightening, the subject of this thread.
The threads in the crankcase should not be a problem unless you don't screw the studs (rods) fully home and are only holding in on couple of threads. Look at a standard full nut and see how many threads you have, there is a reason why they are that thick.
With regard Yamaha manuals not printing torque or wrong figures etc I'll let others discuss :-X
Note the RD200DX engine, although similar and uses some parts from the earlier CS3, CS5 and RD200A & B, is strictly a different animal and the torque figures I can't comment for.
Enjoyed the debate all.
« Last Edit: August 14, 2019, 05:10:12 PM by Astute Greaser »

Online Alistair64

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Re: Cylinder head nut torgue
« Reply #12 on: August 14, 2019, 09:12:26 PM »
So, the "Yamaha figure" is between 7 and 10 lbft depending on which reference you use.   ;)
The points about long studs being under stretch etc are correct.  If you can't get OE studs, then it becomes a question of Hobsons choice!  I have found that some of the sets for sale are nicely made and should be fine.  :)

5port

The Yamaha figure must be between 5 and 10 - take a look at the Supplementary Manual for the DX on this site.
It's not even a typo, because the metric figure also equates to 5 ft-lb (0.7), which surely can't be right.

We can't even blame some girlie in a back office being more interested in playing with her mobile phone, because clearly this was written way before the mobile phone era  ;D

Thanks for the info on the studs btw - may not be necessary to replace them after all.
« Last Edit: August 14, 2019, 09:29:34 PM by Alistair64 »
1982 Candy red RD200DX
1986 RD350F1