Hi
Can anyone shed any light on why Honda decided to Oil the threads on the Crankcase Bolts in the MC28 Manual Section 11-4 (detailed below) and keep the Torque values within the MC18-21 Torque values.

I can understand oiling the Bolt Flanges and was considering applying Anti Seize to the Bolt Threads myself, but lowering the Torque value by 25%.

Has anyone any views on this, I would be very grateful?

Many thanks

Philip

Place the Upper Crankcase onto the Lower Crankcase.
Apply Oil to the Crankcase Bolt threads and Flange surface.

Install the Upper Crankcase 6 mm Bolts and hand tighten.

Install the Upper Crankcase 8 mm Bolt and hand tighten.

Install the Lower Crankcase 8 mm Bolts and tighten in a criss-cross pattern in 2-3 steps. Tighten to specified Torque.

Torque: 2.3 Kg-m (16.6 lb/ft, 200 lb/in)

The MC28 Manual makes it much clearer:

NSR250R crankcase tightening torque
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Hi Andy
Many thanks for getting back to me with the info very much appreciated, however, I was aware of the MC28 diagram, which was the reason for the question really.

Now I’m going to make some assumptions here so please be kind when shooting me down in flames LOL.

I assume there isn’t going to be any, if few differences between the MC18-21-28 Crankcases in terms of the Crankcase Bolt Torque values (probably my first and biggest assumption; sorry mistake).

The MC28 Crankcase Bolt Torque values seem to take a mean value of those given for the MC18 & 21. However, the MC18-21
http://nsr250.net/forums/members/nsr250r_manual_mc16_18_21/index.php#p=153 does not depict or mention the use of lubricant on either the Flange Heads or Bolt threads, is this a possible omission in the Manual?

If it isn’t an omission from the Manual, then taking the highest Torque value of the 8mm Bolts in the MC18-21 Manual of 2.5 kg-m (approx. 18.1 lb/ft, 217.0 lb/in; yes good old imperial measurements so you can tell how old I am) and applying a lubricant as in the MC28 Manual, then a reduction in Torque would be required.

I seem to remember in my Aircrafting days (too many years ago lol), applying a lubricant to a Dry Value Torqued Bolt would require a reduction to it’s Torque value between 15-20%. However, memory probably playing tricks or what! the dear old Internet says a lot more than that, it seems a reasonable accepted amount is 25%.

Therefore, applying a 25% reduction would bring the 8mm Torque Value down to 1.875 kg-m which is a fair bit lower than the 2.3 kg-m stated in the MC28 Manual.

Now I’m probably guilty of making life far too difficult here than its need to be LOL, but are the Torque values in both Manuals correct and HONDA just omitted that the Flange Bolt Heads & Threads had to be oiled?

Anyway that is the case for the defence LOL & closely monitoring any missiles coming my way!!

Take care all.

Regards
Philip

Personally, I would use the most recent information available.

In regard to their assembly, there's effectively no difference between the MC16, MC18, MC21, MC28, or RS250R NF5 cases, and the 94~96 Service Manual is obviously the most recent publication covering the MC16E cases from Honda.

This is from the final release of the MC28 Service Manual:



I'm afraid I am guilty of grabbing the genuine hard copy of the manual (the most common books and a scanner are always next to me!) and looking up the relevant page(s), and then linking our online English version for your convenience. However, I didn't check that the two pages are identical. Please bear in mind the English manuals were created 15-20 years ago, and may not have the most up-to-date information available. As soon as I picked up on the difference, I scanned and remastered the MC28 page for you.

Although I can't find where it states to use a "standard" torque value where none is shown in the 87-93 Service Manual, it does appear in the 1987 RS250R NF5 manual:



Sorry about the aggressive use of watermarks and inverted colours, but once again our images are being copied and used elsewhere with either no credit, or implying they are the creator.
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Andy.
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Hi Andy

Once again many thanks for all the information, time taken and your sage advice it's very much appreciated.

It has probably exemplified that I am very guilty of making life far too complicated than it needs be LOL so it's great to be able to obtain the relevant and accurate information from the experts.

I very much understand the use of the watermarks.

Regards & many thanks.

Philip

I should probably scan the two final edition service manuals I have, but it's another 500 pages... which would then give me sleepless nights due to the fact they're in Japanese! It already niggled me that I didn't translate that MC28 page before uploading it. 🤣🤣🤣
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