Yamaha 50 Themostat Bolt Snapped!

[gibbo500]

After 5 years in hibernation I have recently decided to get my SR4 back up and running.

As expected I knew I would have to throw money at her as many things were seized or corroded however she fired up easily after pre-oiling the cylinders, new fuel and battery. She sounded a bit rough but lovely to hear that 2 stroke rasp again after such a long time

So after stripping and cleaning the carbs, replacing the middle carb cover plate and idle screw (how much!!) and sorting out the gear box seal leak I have encountered a problem that I need some of your expert advice.

Whilst removing the two thermostat bolts one removed easily and the other just snapped off I was only using a 1/4 inch drive so not a lot of force applied and the bolt is below the thermostat plate so nothing protruding. Is there a way of getting this out by drilling / heat or am I best booking it in with a dealer or engineer (£££££)

Oh the highs and lows of boating.......and I haven't even got on the water yet

I will try to get a close up photo this morning but any advice would be really appreciated.

[paintman]

On the basis that you could cause even more problems I'd suggest getting it professionally done.
Recently had the heads off my RRC & one of the inlet manifold bolts sheared - well corroded too. I considered DIY - I've done various extractions over the years - but then thought better of it & took the head to the local engine reconditioners. Cost me £40 but they do have the option of spark erosion if all else fails.

[matata]

Ive been there exactly! Don't worry. Spray some penetrating oil down the hole while your getting bits to do the job. Measure the diameter of the hole.( 6mm?)
Next measure the depth that the sheared bolt is from the surface. Try and find the length of the bolt still in the hole (15mm?). Next I got a guy to make me a metal concentric insert that fitted snugly in the hole. It had a flange on it that rested on the surface. In the centre of the insert was a concentric hole 2.5 mm od. I then used this insert to drill a hole down the centre of the fractured bolt. DO NOT drill all the way through to the end but stop short by say 5mm. Get a piece of steel rod , a snug fit in the hole you've just drilled protruding by say 10cm. tap this rod to help free the fractured stud. More penetrating oil! What your trying to do is break up the oxide corrosion bond. I next drilled it to 3mm.Then I got a anticlockwise 4mm drill bit hoping it would "catch" the broken bolt but that didn't work either. Next up was my 5mm drill bit. Still no luck so I ended up tapping a new 6mm thread and a new bolt and I was back in business!. I considered "easy outs" but if they fracture you really have got problems. The trick is to get the first 2.5 mm hole concentric and axial.The insert was turned on a lathe and cost me a pint. Motor bikers do this all the time! Hope this helps Nik

[Mextli]

Hey

Same thing happened to me, attempted to remove it, broke off the removal tool, attempted to remove that, broke off the hardened drill bit now it just remains as is, thermostat housing is glued on and held with 2 screws.
Outboard cooling systems are not under high pressure like those on a car, so it seems to work fine for the last few years.

If you arent super confident at removing the bolt either let it be done by a professional or leave it where it is.

Luke

[spartacus]

Get it to an engineering shop. Chances are they will have expertise and of course necessary tools to remove. Could be heat and penetrating oil will do the hard-work.

[breezeblock]

don't use easy outs whatever you do if it sheared of because it was corroded in an easy out isn't going to make it magically come out get some pictures up so we can see what your dealing with and offer the best solution

[matt h]

put a nut over the broken stud and a good weld down the centre hopefully should do it

[simzpilot]

While you are waiting to upload pictures you should put penetrating oil on the broken stud. I also use a hammer and punch to tap the broken stud to loosen the build up between the stud and housing. Gentle steady tap and not determined hammering...This along with the penetrating oil may break the seal for the next stage of extraction, Oh, and I never use 'easy out' type extraction tools. I served my time as a fitter back in the 80's so learned the hard way how to do the job right. Several options to get it out and pictures may help us guide you as to the best way

[gibbo500]

Thanks for all your replies chaps it is very much appreciated.

Here are a few pictures of the thermostat housing.





TY

[breezeblock]

clean It with brake cleaner to get rid of the oil put black tape around the hole to protect the face from arcing get a mig or dig welder and build up the remaining part weld on a washer then a nut hopefully the heat will loosen of the corrosion and screw it out failing that take it to a machine shop and get them to do it or try and drill out the core of the bolt yourself accurately doing this is a problem and retap the hole worse case is you have to helicoil the hole

[A1an]

Id pop the stat cover back on and use it as a guide to drill the sheared bolt out.


Cobalt drills and slowly slowly.

[gibbo500]

Thanks A1an & BB some great advice.

I think I will get a professional on it as to be honest I don't have the confidence to do it myself especially if I b*$gger up and make it worst.

Rather than take it to a Marine Engineer or dealer what sort of tradesman carry out this type of work, would a car mechanic be suitable?

TY

[breezeblock]

any machine shop should be able to do it or a broken specialist theres a few on Facebook unfortunately your at the wrong end of Britain for me

[paintman]

Originally Posted by gibbo500

Thanks A1an & BB some great advice.

I think I will get a professional on it as to be honest I don't have the confidence to do it myself especially if I b*$gger up and make it worst.

Rather than take it to a Marine Engineer or dealer what sort of tradesman carry out this type of work, would a car mechanic be suitable?

TY

Not a general car mechanic/garage. You need to find out who your local garages take engines to for crank regrinds, rebores, head skims etc.

[A1an]

There's mechanics and then there's mechanics. Get the wrong one and you'll be wishing you did it yourself.

Machine shop is the way to go if you aren't going to tackle it yourself.

Go on go on go on go on. It's not that hard.

[Searider]

Someone like this:

Welcome to the Thread Doctor Website - Mobile Thread Repair, Hampshire, Berkshire, Surrey, UK

[simzpilot]

If you dont have the tools or experience then take it to a tool shop for repairs. Here is how I would do it and I have the tools and experience.
Measure the good bolt first and work out the tapping drill size for that thread using a Zeus chart. Stay 0.75mm - 1mm below that tapping size when drilling.

(1) Cover all the open ports to prevent debris going into the holes. You dont want a secondary problem later
(2) Using a center punch, mark carefully the center of the broken stud and punch a decent center hole in it
(3) Using progressive drill sizes from 3-4mm upwards drill out the center of the stud
(a) You must ensure to be on center when drilling - This is critical
(b) Use cutting fluid when drilling
(4) When the core is drilled out to within 0.75mm - 1mm Dia below the tapping drill size, use a steel scriber or similar tool to force the stud threads out of the tapped hole in the housing and fold the threaded stud towards the center of the hole. It takes a while but you will fold the broken stud out neatly
(5) Pull the folded stud out of the hole with a long-nosed pliers
(6) Tap the threaded hole where the broken stud was
(7) Apply a light qty. of anti-seize to the two new bolts and start re-assembly

Remember, this is how I would do it and it is not an instruction for works. If you dont have the confidence or tools then take it to a tool shop

[gibbo500]

I have a friend at work that is confident that he can remove it after showing him the engine. He has carbide drill bits and is going to knock up a metal concentric insert guide.

I will keep you updated with progress but thanks again to you all for taking the time to post really useful info