Stripped head bolt studs

OrionSphere

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I bought a bikeberry 48cc kit 2-3 years ago and have had it running off/on.

Recently I noticed that my head area is leaking alot of oil and compression is sucky. One of the head bolts is stripped. I don't know exactly what size I need.

Does anyone know, for sure, exactly what size bolt I need to replace it? Hopefully I can order the replacement on Amazon before I get home and won't have to open it up and measure. I'm riding my bike until I get it fixed.

It should look like this so everyone knows what I'm speaking of.
 

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Hand tighten the studs until they bottom out. It is highly advisable to use a high temp medium strength thread locker (243) to prevent movement of the studs in the case halves. In some cases you may need to use a wrench to drive the studs in until they bottom, but once they bottom out, don't go any further than a tiny snug (IE a 16th of a turn). Studs do not need to be torqued into the holes on the cases beyond a slight snug up after bottoming out, and doing so is a great way to break the case halves or strip the threading out again. I have built every engine this way and have never had an issue.

I also suggest not using the acorn nuts as the primary means to secure the head. I use them as a lock nut on top of a standard nut mainly for weather protection to the threads. I also use wide washers, bevel side down, and a lock washer on top of that to help prevent it backing off (combined with said lock nut is slightly overkill, but there is no kill like overkill.) I run the wide washers bevel side down to allow the head to expand and contract without greatly affecting the stud and other steel hardware. It's not really a necessary thing, I just do weird stuff because of my experience with working on and repairing other types of machinery.

Get an inch pound torque wrench if at all possible, but a light foot lb (say, up to 15-20ish) will also work. The standard torque is 12ft-lbs (dry). I go to 15 with upgraded hardware, but that's a me thing and not advice. I do mine in 2 stages, 10 in a criss cross, then 15. Again, not necessary really, but I always prefer to tighten most gasket sealed items in stages to allow better/more even compression of the gaskets and a more accurate torque bolt to bolt.

You can use loctite on the top nuts, but be aware that it acts as a lubricant to the threads which changes the torque applied to the fasteners. If you do, Loctite specifies that you reduce the torque on the fastener by 20% vs. the dry spec., which is 9.6ft-lbs or 115in-lbs. I use 243 on mine combined with said washer, lock washer, and the acorn acting as a lock nut (Trust me, I am nowhere near close to bottoming it out, so don't bother telling me I am wrong). You could probably skip the lock washer TBH, but again, there is no kill like over kill. :sneaky:
 
By the way, if you use Loctite, make sure it is 243, which is the high temp stuff rated to about 350 degrees. It won't melt under normal operating temperatures of a typical 2 stroke, and if it does you were approaching critical temps anyway.

If you want an even higher temp rated blue loctite you will need the ceramic based 2422. That is rated to 650 degrees, and trust me... it holds. I use it on rifle hardware. It only comes in a syringe style tube and it's not the cheapest stuff ever. but you do get quite a lot of it too. I bought my last one 4 years ago and still have 2/3 of it left after several engine and rifle builds/repairs.
 
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An alternative to heli coils is to (if you're using the 6mm bolts)
Drill and tap the hole out to fit a 8mm bolt red lock tight the bolt into the hole.
Then cut the bolt off flush with the cylinder and drill and tap the cut off bolt to fit your 6mm mounting stud
 
I think I will just stick with rethreading or helicoils...This video looks like the long way around the barn to me...lol...lol.
Agreed. Helicoils are more than sufficient for holding a stud in. Studs are not under any significant axial torque. Studs are literally used because of this, and it allows for more accurate and consistent torque for clamping. The primary force applied to a stud is tensile loading. My only suggestion to anybody doing a helicoil repair is to get the longest one you can that will fit in the hole so you have as much thread engagement as possible.

That said, if you REALLY want to go all out crazy on a hole repair, such as a stripped out helicoil hole, Filling it with weld, milling, and re-drilling and tapping is the best way. These cases can be had for about 40 bucks though, so it really isn't worth it IMHO. Just get a new case half set at that point. Alternative repair would be to bore the stripped hole clean of threads, then tap it again with a bottom out tap, then die the same threads into aluminum bar stock. Use an epoxy like alumabond and screw in your aluminum threaded rod, cut flush and deck, let the epoxy cure, and drill and tap a new hole into that.

I'm lazy and I have 40 dollars. I would just buy new case halves if it went that far, but some people love to fix stuff even when it doesn't make sense to do so.
 
Agreed. Helicoils are more than sufficient for holding a stud in. Studs are not under any significant axial torque. Studs are literally used because of this, and it allows for more accurate and consistent torque for clamping. The primary force applied to a stud is tensile loading. My only suggestion to anybody doing a helicoil repair is to get the longest one you can that will fit in the hole so you have as much thread engagement as possible.

That said, if you REALLY want to go all out crazy on a hole repair, such as a stripped out helicoil hole, Filling it with weld, milling, and re-drilling and tapping is the best way. These cases can be had for about 40 bucks though, so it really isn't worth it IMHO. Just get a new case half set at that point. Alternative repair would be to bore the stripped hole clean of threads, then tap it again with a bottom out tap, then die the same threads into aluminum bar stock. Use an epoxy like alumabond and screw in your aluminum threaded rod, cut flush and deck, let the epoxy cure, and drill and tap a new hole into that.

I'm lazy and I have 40 dollars. I would just buy new case halves if it went that far, but some people love to fix stuff even when it doesn't make sense to do so.
Thats pretty much exactly what I was talking about
 
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