Yamaha RXS Cylinder head stud size for helicoil?

[skeverd]

Hello,

Does anyone happen to know the stud size for this bike as i have recently discovered a stripped thread in the cylinder.

I was gonna try and purchase a helicoil kit however i have no idea on the size - there are no visible markings.

Thanks.

[2Smoke]

Hello, which stud would that be? The head studs on the top of the barrel or the exhaust studs?

They should either be an m8 or an m6, you could guesstimate with a ruler if needed but digital calipers are an accurate way to measure and very cheap to buy.

I'd bet on it being an m8 (8mm) if it were the cylinder head studs.

Paul
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Currently in the stable.. '89 TDR250, 86 NSR250 '79 350LC, '79 DT175MX, 82, Pasola, '98 R1, '95 Speed Triple.. all of them total sheds..

[skeverd]

It is for the cylinder head.

What does the 'm' mean for the bolts? im guessing the number is the bolt diameter, it the 'm' the thread how fine/course the thread is?

it also uses a 12mm nut size on the stud if thats any help?

Thanks again.

[skeverd]

Also the helicoil kits seem to be stuff like m8 x 1.25. what is this second number?

btw, i just firgured the m is for metric.

[2Smoke]

Ok, if its a 12mm nut then it'll be an 8mm thread. Should be m8x1.25 as a standard thread.

The 'm' stands for metric so working in millimetres to determine the thread pitch and size (as far as I remember anyway!).

Are you going to be doing the helicoil repair yourself? It can be easy to screw up if done incorrectly (done it myself too many times, overconfidence..) and you'll have a job taking it up to the next size (m10) if it does go wrong. Just a word of caution like..

Good luck anyway
Paul
____________________
Currently in the stable.. '89 TDR250, 86 NSR250 '79 350LC, '79 DT175MX, 82, Pasola, '98 R1, '95 Speed Triple.. all of them total sheds..

[2Smoke]

the 1.25 is the thread pitch
https://www.bonaero.com/images/Pitch.GIF

Paul
____________________
Currently in the stable.. '89 TDR250, 86 NSR250 '79 350LC, '79 DT175MX, 82, Pasola, '98 R1, '95 Speed Triple.. all of them total sheds..

[skeverd]

Right, it all makes sense now thanks

What do you mean about being careful? what do i have to be careful about when doing it? anything in particular to look out for?

it seems I've learnt much about bolts and studs today, thanks

[2Smoke]

Well, its not quite a straightforward job to replace the thread!

You'll need to drill out the old thread with the supplied bit, there is a risk here of going in at an angle or drilling too deep (ooer) thus knackering the cylinder!

Same with cutting the new thread for the helicoil to go into, if you get it wrong you'll be looking at a replacement cylinder again!

You'd need experience really of how to do this, maybe practice on some scrap bits first?

I'm all for doing stuff yourself but maybe it'd be worth getting someone a bit more experienced to do it? The cost of a helicoil kit would maybe be more than what someone would charge to do it (including the helicoil) and there is no risk of trashing a cylinder!

Up to you though, I dont know your circumstances!
____________________
Currently in the stable.. '89 TDR250, 86 NSR250 '79 350LC, '79 DT175MX, 82, Pasola, '98 R1, '95 Speed Triple.. all of them total sheds..

[skeverd]

Well i'm a trainee mechanic so i'de prefer to learn form it and get used to using them - i'm pretty used to working with metal also. I've just never had any reason to do anything with helicoils before, thus would be a learning experience in my eyes. yea i could send cylinder away to be done, however i feel doing it myself would be a more valuable experiance regardless of possible outcomes.

Surprisingly they don't teach us much about thread construction. So thanks again for all the help.

[27cows]

Unless the barrel is in exceptional nick (ie recently rebored) then just scrap it and buy another second hand. Much less hassle and probably cheaper. If you've got a 'soft' barrel then then chances are that stud (or one of the others) will pull again. A handful of RXS barrels seems to be made of the same peculiar material they constructed Superdreams from - tensile strength somewhere between chocolate and cheese.

If you do decide to have a go yourself, bear in mind that you'll need access to a pillar drill.
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The RXS100: vehicle of choice for Chuck Norris

[Robby]

See as the barrels are so cheap on those bikes, it doesn't matter so much if you trash it learning to do a helicoil.

Pillar drill is a must, but they can be had very cheaply - mine was under 40 quid on ebay and does the job for this sort of thing. Mark how deep you want to go on the bit, or set the drill stop. Use a proper tap handle to screw in the tap, the handle isn't supplied in the cheap (£20 quid silverline or draper) helicoil kits.

If the threads are all soft then it is worth helicoiling all of them, you get a stronger thread than one in plain alloy. A timesert is a far superior version of a helicoil, but also more expensive. Remember to use a smear of copper grease on reassembly, you don't want to have a nut seized into a helicoil next time you have to pull it apart.

[stinkwheel]

Just a slight warning. Measure the thread carefully unless someone comes on who absolutely knows for a fact what the correct thread is.

Get a set of verniers and measure the width of the stud to the outside of the threads. Could be 6, 7 or 8mm. Next get a thread guage and check the pitch. Could be 0.75, 1.00 or 1.25. If you're a trainee mechanic, this would be a good time to learn how to use these tools.

Armed with these two numbers, you'll be able to order the correct helicoil kit.

The reason I mention this is that I know for a fact that the Yamaha YB100 uses an M7x1.0 thread on the engine studs.

M7 is a ball breakingly stupid thread to use because it is rarely used on anything but certain parts of French cars. As such, the nuts are difficult to source (as in you have to go to a fastner specialist). I would imagine an M7 helicoil would be similarly tricky to obtain.

To add insult to injury, the YB also uses a non-standard hex size on the nuts.

I mention this because the YB and RXS production runs overlap and they are both, 100cc, 2-stroke yamahas. Not outwith the realms of possability they used the same thread on both.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[27cows]

I'm 95% sure the RXS barrel studs are M8/1.25.
____________________
The RXS100: vehicle of choice for Chuck Norris

[Bezzer]

[Ed Case]

I've got an old 250RSA with eleven out of twelve 6mm helicoils in the cylinder head courtesy of some twat screwing Whitworth bolts in when he couldn't be arsed to use the real things, so I'm a bit of a fan of the things but in the plug-hole I've had put in a 'Timecert'. These things seem to me to be a better deal on the larger sized applications as I have in the past had a helicoil come unscrewed with the bolt. On the other hand, perhaps those particular coils had been put in by a right divi who didn't know what he was doing.

[skeverd]

Thanks for all the replies, I've ordered a m8 x 1.25 coil kit.

The cylinder has recently had a fresh bore, thats why i'm investing in the coil kit, i'm gonna practice drilling some more first and either tomorrow or Wednesday i shall take it easy and go real slow when boring the stud hole.

i did measure with a tape measure as i don't have access to a micrometer until Thursday, thats why i ordered the kit i did. i shall check the size first by winding the bolt into coil and seeing how good of fit it is.

[Ed Case]

Good man, best of luck............Ed.

[skeverd]

Good news! I done the helicoil in the cylinder and all went well. I had theories of making a guide for the drill bit in order to ensure a verticle bore was attained - but in the end i done it freehand.

The bikes now running great! so i'm chuffed.

Thanks again for all your replies.

Shamen.

[Ed Case]

Cracking news skeverd, pleased it went well.