Starter Motor Clutch – Yamaha Conversion

[Anonymous]

I have been using them on my CB1100F’s for the last few years, and have now fitted them to my RC’s

One of my CB1100F’s has a 1123 piston kit and a CB900F Head fitted so has far higher compression than a R engine, always starts easily with no slipping or grinding noises

I have always used R6 sprag clutches from ebay, they all have been used ones and i figure if they have been used on a 600cc engine they have had an easy life

The other thing i would recommend is to fit an AGM battery, these have far more CCA (cold cranking amps) I use the Motobatt ones from ebay, and rebuild your starter motor with new brushes, they tend to lose power when the brushes wear down,

There are Chinese copys of the R6 sprag clutch about which i have heard do fail you can tell the genuine Yamaha ones as they have a Yamaha part number on

Keith

[Anonymous]

Here is the document i have sent to Andy to include in a future Magazine

Anyone who has owned a CB1100R CB900F CB750F for any amount of time will tell you that one of the most troublesome parts can be the Starter clutch especially on the 1100s and more so with a big bore piston kit fitted

I am a member of http://www.cb1100f.net as a few of the R owners club are. A few years ago an Australian member DonR built a 1123cc engined CB900f which he soon discovered the stock Honda starter clutch was not up to the job required

So he searched for a more modern replacement and by chance found that a 1999-2001 5EB Yamaha R6 starter sprag would fit with a slight modification

As you can see from (photo1), the Yamaha Sprag clutch has around 20 fingers which grab the Starter Clutch Gear compared to the Honda’s 3 rollers (photo 2)

When I saw this posted I bought a couple of R6 Starter sprag clutches from ebay and set to work making them fit 2 of my CB1100F’s which had both been rebuilt with CB900F Cranks and 1123 piston kits

The other reason I went down this route is that Honda made the Splines on the 1100 starter drive flanges slightly tighter so they will not fit a 900 crank without a lot of force, but a 750/900 starter drive flange does fit a 1100 crank ok

Its is reasonably easy to do but as you can see from photo 3 (1100 beside a 900) there is not much room to put any more holes in the stock CB1100R starter drive flange so you will have to source a 750/900 starter drive flange and a starter clutch gear

You need to source these as a pair as you cannot mix 750/900 and 1100 parts as the 1100 starter drive flange has a slightly larger spigot

Also using the 750/900 parts allows you to fit 6 bolts (I use the Yamaha Torx bolts part(Yamaha part no 90149-08031-00 ) and with double the amount of bolts I have now used my Bikes for 2 years with no problems and they always start easily with no slippage or nasty noises and no bolts coming loose

What you need to do to the 750/900 starter flange gear is to put 6 new 8mm holes in it

If you have a friend who works in engineering they can easily drill 6 new holes in the correct place

Or option 2 is the method where I made a discovery, when you by your Yamaha part it may come with the generator flywheel which has 6 holes (photo 4) in it but Yamaha only use 3 bolts, probably as a R6 does not need much to spin it

If you mark a line midway between the hole in the Yamaha flywheel you can then line one of the existing holes in the Honda starter flange to position it

I found the Honda starter drive flange is a good fit in the tapered hole of the Yamaha Generator Rotor and when you put a bolt through it clamps nice and central, so you can use the Yamaha part as a drill jig (photo 5)

When drilling you will need a 8.5mm drill to start with (Photo 6) as this is the size of the hole in the Yamaha Generator rotor
You just need to drill a slight indentation with this drill, then you can drill right thru, I used a 5mm drill, then a 7.5mm drill and finished the holes with a 8mm machine reamer (Photo 7), this will give you a good location when fitting the new Yamaha Torx Bolts

The Honda Starter flange gear is quite soft to drill through

The other part that will need a slight modification, depending on the wear on the Honda starter clutch gear, which if not worn will need a tiny amount grinding off as the stock Honda gear is approx .006’’ .15mm larger than the Yamaha part(42.18mm)
There again you will need to find a friendly engineering friend to help you out

Photo 8 shows the Honda CB750/900 Starter gear ground down ready to fit, I would also recommended having a small 30 deg chamfer ground on to help the fitting of the Yamaha sprag clutch over

The other thing I would recommend is to use a more modern Gel Type battery

I have fitted Motobatt AGM batterys to all my bikes, the have far more CCA (cold cranking amps) than the old Lead Acid type and are maitainance free, and they will not leak battery acid all over you pride and joy

Also giving the starter motor an overhaul helps greatly, as when the brushes wear down they do not work as well as they should, a new set of genuine brushes are under £15 from David Silver Spares

Photo 9 shows the R6 conversion on the Crank

[Anonymous]

Photos 1-4
[IMG]http://www.cb1100r.net/forum/attachment.php?attachmentid=1713&stc=1[/IMG][IMG]http://www.cb1100r.net/forum/attachment.php?attachmentid=1714&stc=1[/IMG][IMG]http://www.cb1100r.net/forum/attachment.php?attachmentid=1715&stc=1[/IMG][IMG]http://www.cb1100r.net/forum/attachment.php?attachmentid=1716&stc=1[/IMG]

[Anonymous]

Photos 5-8
[IMG]http://www.cb1100r.net/forum/attachment.php?attachmentid=1717&stc=1[/IMG][IMG]http://www.cb1100r.net/forum/attachment.php?attachmentid=1718&stc=1[/IMG][IMG]http://www.cb1100r.net/forum/attachment.php?attachmentid=1719&stc=1[/IMG][IMG]http://www.cb1100r.net/forum/attachment.php?attachmentid=1720&stc=1[/IMG]

[Anonymous]

Well thanks guys. I didn’t read this thread in time as I’d been rebuilding the clutch and gearbox on my old Triumph Model P (1925) for yesterday’s Banbury run, and then went straight into fitting a CB750 sprag clutch bought from Holland to the CB1100R. It works fine (for now!) but I will definitely be looking at the R6 retrofit as it seems a much better solution.

As a matter of interest, these are the bits that came out of the old clutch. Note that the three plungers are different lengths! i guess the cracked rotor won’t help much either.

[IMG]http://www.cb1100r.net/forum/attachment.php?attachmentid=1721&stc=1[/IMG]

As for the Classic event at Spa, I’ve taken off most of the shiny bits, fixed bits of the fairing with fibreglass patches on the inside, sealed up the 4 into 1 exhaust gaps (too noisy for Mallory perhaps?), and I’ll take some starter rollers in case the CB750 starter clutch lets me down. I’ll let you know how I get on !!

Cheers

Gareth

[Glenn Kirkham]

Mmm – that doesn’t look right Gareth… I thought the plungers were all the same..?

[Anonymous]

Yes the plungers should all be the same length Glenn, and the springs all need to be in good condition to work correctly, and it pays to check the rollers with a micrometer in a few places around the diameter, they take the shape of the old Three pence pieces, they develop small flats round them which causes problems

To tighten the bolts correctly on the stock clutches you need to grind the lead-in chamfer off of a 6 point 12mm socket to get the maximum grip on the shallow hexagon headed bolt, and some high strength loctite on the threads

Keith

[Glenn Kirkham]

I guess I must be lucky – “touching wood” – the 3 bolts were loose on my RB when I got it (I think that’s why the guy wanted to sell because of the horrible rattle). However having cleaned out the threads and loctited them back never had any issues at all in 15 years..

Cheers.. Glenn

[SteveB]

I have just won a R6 Sprag clutch off ebay, now I need the other 750/900 part. Anybody got one ? ta steve

[Anonymous]

Hi Steve,

Indeed I do have the bits you need. I bought a CB750 starter clutch complete and took out the sprag section and have all the bits left – see eBay : http://www.ebay.co.uk/itm/272288558191

Let me know if you want it for “mate’s rates” !

Yes Glenn, the plungers and springs should all be the same length. I did wonder if one was shorter to act as a “lead” but looking at the spares diagram and the original parts list, they should all be identical. Curious, as I’ve had this bike since almost new (540 miles) and I haven’t had the clutch apart. Mmmm. The sprag base, which looks copper plated, is cracked [IMG]http://www.cb1100r.net/forum/attachment.php?attachmentid=1723&stc=1[/IMG] and the opposite ends of the plungers had pushed out through the outer plate [IMG]http://www.cb1100r.net/forum/attachment.php?attachmentid=1722&stc=1[/IMG], but the rollers are all perfectly round. Bear in mind this bike’s seen very little use (9,000 miles) so I’m surprised it was so bad.

I’ve got the Spa Classic Bikers event coming up this weekend so what I’ve done is put on the CB750 sprag section, blue loctited and properly tightened up the three bolts, and hope it lasts the weekend. Then I’ll get an R6 clutch and retrofit it.

[SteveB]

@GarethR 3767 wrote:

Hi Steve,
Indeed I do have the bits you need. I bought a CB750 starter clutch complete and took out the sprag section and have all the bits left – see eBay : http://www.ebay.co.uk/itm/272288558191
Let me know if you want it for “mate’s rates.

Yes ,please send me a txt message with price, thank you. 07811109485

[Glenn Kirkham]

Oops.. think I may have just bid on those…😕 Happy to stand down for you Bozzy. .

[SteveB]

@GlennK 3770 wrote:

Oops.. think I may have just bid on those… Happy to stand down for you Bozzy. .

Thanks Glenn, just waiting for info from Gareth, maybe after he gets back from Spa ?

[FrancescoS]

CiaoScrivo dall’Italia, ho lo stesso problema, non so come farlo, nemmeno i pezzi di ricambio in Honda.puoi spiegarmi meglio come fare il cambiamento ..mi scusi per il mio inglese..Grazie

[Author]

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