M8 X 1.25 tapped too big

I have an 89 RM250. I managed to strip out one of the cylinder head bolts, and had to tap it. This was one top end ago and it was my first helicoil to put in. I put one in since then and it when in correctly, but the first one (which held through the first round for minimal time) was tapped too large. I tried to get it in again today and it was pretty much a useless hole. I know that I should probably go one step larger and do it again, but I'm worried that moving to M10 will be too much for the cylinder. Instead, I put the helicoil in with a little bit of metal filler around it to hold it, but I'm not sure if it will work. I'm letting it sit over night to let it cure, but I'm pretty sure I still won't get enough torque out of the thing. What should I do next if this doesn't work. Local auto parts places only have M10. I have a coil and a bolt for M10. However, I only have a tap for M8.I will also have to drill out the head to make the bolt fit. Not to mention running out of metal in the cylinder to work with.

I was wondering if maybe I could use a standard size that would be only slightly bigger. I don't want to mar up the head too much or mess up the cylinder as that would be awful costly. I plan to make a trip to the local bolt store soon if I check it tomorrow and the coil comes out pretty easily. The "sand drags" are coming up the last weekend of Feb. and I only have two nights a week on it to work on it until then. I will be pretty left out if I don't have a toy by then, and any tips to make this work before then would be helpful. I don't want to risk too much trial and error and run out of time or metal. PLEASE HELP!

Sorry if this sounds kinda like I'm rambling. It's late and I've spent all day working on stuff (my brain is fried),

So this goes into the top of the cylinder and not into the case, right? If that's the deal then there is no reason you can't just do an M10 and drill the hole in the head out a bit to accomodate. I would caution you to use only coarse thread stuff, fine threads in aluminum tend to not last too well.

If there's not enough room to do the M10, 3/8" is real close to M9 and might do what you want. FWIW, it helps to use a stud rather than a bolt; running bolts in and out of aluminum threads tends to wear them quickly.

Use a "KeenCert" or TimeCert kit instead of the helicoil there thicker waller inserts. Keencerts have locking spikes.

MSC and McMaster have them.

Thanks for the info guys. Both answers were exactly what I was looking for. I live in Ama, Tx and we don't have MSC or McMasters. So, I would have to look online probably. I checked the how well the liquid metal held today when I had a free moment by putting an M8 in and pulling on it pretty hard with my hands and it didn't move. Hopefully it will work, but I will write down your answers for when I get a chance to work on it here in a few days. Even if I don't use your answers now there is a good chance I will need an alternative the next time I put in a top end. I tend to go through a top end pretty quick as far as hours ridden go. So even though I don't get to ride but once a month I have to do it about twice a year. Probably the reason I'm having to resort to this sort of thing to get it to work.

Thanks Again, Dillon

PS yes it is in the cylinder, not the case. Nickasil sleeve with aluminum cylinder. I think I'm gonna try and get by a bolt company and see if I can get a stud instead before I put it back together.

McMasters ships. Really fast, too. Like, you order it today and you'll have it tomorrow, or the next day at the latest. www.mcmasters.com. I, personally, would not trust a head bolt to liquid metal.

Head bolt did not hold up with liquid metal. Figured it was a long shot anyway. I also found another stud that needs some sort of attention as well. Since I had it all the way back together I rode it around for a minute then the head gasket blew again. (knew it was coming, but knew I was gonna be doing it again anyway so it didn't matter) Back to the drawing board. I think I'm gonna order three of a different type of insert. One possibly larger than M8. Then order some studs because I'm not liking this bolt business anyway. Order new gasket kit and another one of those little spinwheel thingies that works like a water pump (i think it's overheating too). Then I should be good to go. Will order parts and commence surgery next week. Keep you posted.

Timeserts are available on Amazon.

http://www.amazon.com/TIME-SERT-Metric-Thread-Repair-1812/dp/B001JK44LG/ref=sr_1_1?s=automotive&ie=UTF8&qid=1294634290&sr=1-1

Cant begin to tell you how well these work when used correctly.

Also see here http://grassrootsmotorsports.com/forum/grm/pulled-head-stud-helicoil/29413/page1/

I would think this would be a good application for Twinserts. Basically double helicoil. Twinserts

TuffWork wrote: Head bolt did not hold up with liquid metal. Figured it was a long shot anyway. I also found another stud that needs some sort of attention as well. Since I had it all the way back together I rode it around for a minute then the head gasket blew again. (knew it was coming, but knew I was gonna be doing it again anyway so it didn't matter) Back to the drawing board. I think I'm gonna order three of a different type of insert. One possibly larger than M8. Then order some studs because I'm not liking this bolt business anyway. Order new gasket kit and another one of those little spinwheel thingies that works like a water pump (i think it's overheating too). Then I should be good to go. Will order parts and commence surgery next week. Keep you posted.

One possible solution is to jump over to SAE Inch to fill the gap between 8mm and 10mm. For instance, a 3/8-24 thread is roughly 9.4 mm, which could be the difference between "it works" and "oh cr*p."

Also, a BIG second to the Timesert idea. Love those, especially paired with studs.

I know this thread is a bit old, sorry I didn't see it sooner.