Removing cylinder/damaged engine bolt?

[Magua]

Finally made a start on my engine last night with the help of Xwhatsit (legend).

All of the engine bolts came out out of the head with varrying degrees of difficulty except one for. This bolt was determined not to move. After applying what felt like all the force in the world it made an allmighty crack and started to spin, but still with great difficulty. It's pictured below and not looking too great. What could cause those few threads to fill in as they have? Threading from the case?

Both Cylmer and Haynes manuals tell me just to 'lift the cylinder up and off', whereas mine seems to be rather stuck. Other than continually whacking it with the rubber mallet/block of wood are there other avenues to follow?

[Max Preload]

Those few threads have filled in with the top section of thread from the engine case. Helicoil time.

[Magua]

Those few threads have filled in with the top section of thread from the engine case. Helicoil time.

Lovely. So I imagine a Helicoil, to rethread a hole, would need to widen it a little. Which means I'll have to get a new bolt made?

[vifferman]

I dunno if you need to helicoil the hole - dpends how knackered it is. Probably best in the long run (do the job right, do it once. etc.)
Yes, to fit a helicoil, the hole needs to be drilled slightly larger. But (however!) the helicoil means the thread size is the same (no new larger bolt needed).
Don't forget to clean up the threads of the bolts before you replace them.

Does the barrel have bits (a skirt) that poke down into the case? If not, then it should eventually come off. Just be sure you spread the force over a large area so you don't crack/bend fins.

[The Pastor]

man that is a dirty thread!

[xwhatsit]

man that is a dirty thread!

Yeah. It feels gritty but it's not hard -- I wonder if it's some sort of gasket gunk crap.

@Max Preload: That's what I thought too but when I've pulled threads out like that generally you can see that the threads are separate, if you get what I mean. Sometimes you can get your fingernail underneath and peel the whole thing out. With this, those flat bits look like they're part of the same steel, completely seamless and filled in.

Helicoil on a cylinder head bolt thread in the crankcase? Will it be strong enough?

The real PITA is the stuck cylinders. Can't do anything without getting that off.

[Magua]

I've been bashing away at the cylinder with my rubber mallet. All I've achieved is to chip away at my mallet.

[vifferman]

I've been bashing away at the cylinder with my rubber mallet. All I've achieved is to chip away at my mallet.

Hmmmmm......
Hmmmmmmmmmmmmmmmm.....
Try putting a block of wood against the barrel and giving it a sharp whack with a hammer/the rubber mallet/a small sledgehammer. You need something that's gonnna break the base gasket loose. Alternatively (or as well), if you can gently poke/tap a very slim knife blade into the gasket (not either side, in case you damage the face), you might wound it enough to make the fucker let go its grip...
Looking at your pix, if you levered the barrel upwards where the fins have webs between them, it's unlikely to snap or bend them, so that's another possibility.
The main thing is whatever you wallop/lever is walloped/levered over a decent area and/or is supported or strong enough that it won't bend or crack.

[Ixion]

The thread looks munted, but there may be enough left to hold.

Is the head separately bolted to the barrel ? If so you can try putting a bit of wood on the top of the piston, and bolting the head in place. Turn crank, piston comes up, and bit of wood meets head pushes head up, head pulls barrel up. Make sure you have the cam chain off so the valves don't try to open. Best not done on a built up crank.

Edit Are you sure you have removed ALL barrel holding down bolts/nuts? Really sure? really really ? Go take another look. Get someone else to take a look.

[vifferman]

'bout time you showed up Les.

[xwhatsit]

Edit Are you sure you have removed ALL barrel holding down bolts/nuts? Really sure? really really ? Go take another look. Get someone else to take a look.

I had a separate look, but then again I'm the guy who didn't bolt his cam sprocket up tightly enough and caused quite enough spectacular damage for his own wallet.

Head bolts go right through to the crankcase. No separate bolts, apart from the camchain tensioner garbage, of which there is only one. Very simple little motor.

We weren't particularly enthusiastic about jamming knifeblades and such into the gasket surface, part of reason for taking it off is to replace the slightly leaking base gasket and scratching the mating surfaces isn't likely to help.

[Ixion]

Do you have a heat source? Heating the area around the joint may help.

[MSTRS:Me]

I'd be putting a piece of wood on the crankcase and using a loooong lever inserted under the bottom fin, gently prise the cylinders upwards. Once off, you will know whether the crankcase thread is stuffed (helicoil had it). It is an easy fix for a proper engineering shop.

[Max Preload]

Edit Are you sure you have removed ALL barrel holding down bolts/nuts? Really sure? really really ? Go take another look. Get someone else to take a look.

I second that. Nothing down behind the camchain tensioner guides?

@Max Preload: That's what I thought too but when I've pulled threads out like that generally you can see that the threads are separate, if you get what I mean. Sometimes you can get your fingernail underneath and peel the whole thing out. With this, those flat bits look like they're part of the same steel, completely seamless and filled in.

Try spinning a nut over it - I think you'll find it moves up the bolt ahead of the nut. Or give it a scratch with a scriber - that'll show if it's soft.

Helicoil on a cylinder head bolt thread in the crankcase? Will it be strong enough?

Plenty - but it has to be done properly - any misalignment and it'll majorly upset the head torquing.

[Magua]

I wanted to use this, simple solution. Then I read the fine print, doh.