Undoing a *really* stubborn bolt

My brother’s SR125 is in dire need of a couple of new gaskets, one of which we cannot separate. It’s between the barrel and the crankcase.

The two bolts arrowed in the below (atrocious) picture (a new one should be forthcoming) refuse to undo:

We’ve tried lots of WD40, and even more torque, but bent the allen key, and I’m after some more suggestions to get them undone. With the head off, there’s plenty of access from above, but only in a groove about 10mm diameter in the fins.

I’ve had heat treatment suggested to me, and this sounds reasonable, but surely it’s already getting heated and cooled quite regularly, being the bit that holds the barrel to the crankcase? What would my round of heating and cooling do to loosen it off?

direct heat will make the two different metals to expand at differnt rates so you may be lucky that it will undo … you just need to be careful that you a dont set bike on fire and b damage any other gasket or seal around the area

If you can get a allen key bit in there ( i cant remember my old sr sorry ) and then if possible to impact this bit to try and jar the bolt a bit this may allow it to loosen with the added heat …

from what i remember yes they are a pig to get to …

Only way you’re going to do it properly is with the correct size hex bit on the end of a socket wrench with extension bar.:slight_smile:



don’t use a long lever, if the bolt is as tight as it appears you are most likely going to round off the allen bolt head, get a tight fitting allen key (not all allen keys are exactly the correct size) if possible get some heat onto the casings first or get some cold spray onto the bolt, the purpose being to cause unequal expansion between the 2 metals. then the fun part! hit the allen key with a big hammer! it is important that you hold the allen key down into the bolt (don’t hit your hand) and make sure you don’t hit the engine fins as they are fragile, the shock loading of the impact is far more likely to start the bolt moving than the slow build up of torque from a lever, size of hammer depends on access and confidence, but generally mongo-sized is the way to go :slight_smile:

Get heat on in…Then use the right size allen key in there…the socket type is best…if no good…I always whack a snap on bit in there and crack it round…

The big problem with hitting it is doing so without moving the allen key in the head. The bolt head’s already slightly deformed from finding that out (and I’m pondering ways of negating that issue, too). I can’t find an extension and allen socket for an impact driver that fits in the little groove in the fins, either.

Things You’ll Need:
Penetrating Oil
Penetrating Oil
Work Gloves
Work Gloves
Cold Chisel
Open-ended Wrench Or Socket
Propane Torch or Heat Torch
Rubber Or Wood Mallet

Heat the connection with a propane torch or Heat Torch if you can do so without any risk of damage or fire. It helps draw penetrating oil into the threads (see step 2).

Apply a liberal amount of penetrating oil in and around the joint, then wait … and wait … and wait. It can take anywhere from 10 minutes to several hours to loosen the joint.

Strike the head of the bolt or nut with a cold chisel to shock the connection.

Apply a socket/Allen key of the proper size, and rap its handle sharply with a rubber or wood mallet.

Soak the bolts in penetrating oil and leave overnight. ‘Plus Gas’ is a good one to use. WD40 is not as good

maybe also try shocking it with a hammer fomr the top, centre punch it if you can. leave it soaking over night etc. it sucks man i know!

if you can find one that you can get into place a torx driver can be hammered into an allan bolt to get over any distortion, other than that you can use a cold chisel and hammer to tap the bolt undone, again takes a bit of care and nerve.

Doing it this afternoon, while we were waiting for the engine to cool to take the exhaust off I had a quick go with an allen key 'cause I was bored, and they turned!

So they’re off now, but the barrel gasket’s taking a lot of patience to remove…