Not a barrel of laughs

[Nicko]

Hello again, I have had a look at past threads and found plenty of interesting information, but not specific to this problem;

when I stripped the engine I noticed the head gasket had blown in two place, but got on with aqua blasting the engine.
once cleaned up i noticed one of the head studs had eroded adjacent to one of the blown gasket poinuts, so I have removed the stud and sourced a replacement. Investigating the reason I have found one of the liners is not in the correct position and is 0.25 mm lower than the barrel/cylinder head surface. I found a good thread on the website about removing the liner, my possible courses of action are;
1/ reposition the liner and shim the liner up .25 mm with a home made shim of aluminium foil
2/ a local machine shop said they would skim the barrel top including the 2nd liner top to make all level.
3/ source a new set of barrels
4/ do nothing but fit a modern gasket in the hope it seals this time
5/ anything else the forum might suggest ?

I have attached a couple of photos as last time, any help greatly appreciated

 

[Signal]

I would skim the head and source a good second hand barrel . There are a lot of 750cc conversions that have been done. Most these days using the big fin barrel kits.
Alternatively go for a new 750 kit you probably will need new pistons etc anyway.

 

[Jim]

Barrel of laughs....

I wouldn't worry about repositioning the liner. If you look closely at the cutout, it's not interfering with the machining for the alignment bushing that goes in there, so it's position is fine. Looks odd I'll give ya, but I've seen a lot of 'em like that, that worked just fine.
Out of curiosity... was that bushing missing? It looks a bit dirty down in the hole.

To your question... I'd let the machine shop skim the head 'till the barrels are flush and call it good.... providing the barrel is otherwise OK that is.
Or... as Signal says... hot rod it with bigger jugs.

 

[Jim]

Almost forgot....
Remember that these are interference engines. After the skimming, I'd highly recommend modelers clay on the valve pockets to check piston and valve interference/clearance.
I can't remember for sure but a minimum of .050 sticks in my head. Maybe someone else here remembers the actual minimum clearance?

 

[Signal]

From my notes taken from the XS performance guide Piston to valve clearance Inlet .050, exhaust .065. Skimming the head will also alter the cam timing slightly but this could be compensated for with thicker base gasket if you are worried about it.
Piston to head clearance from Smed speed .030, XS performance guide .035.
With stock gaskets there is a lot of clearance piston to head but you must check it as you don't know what has been done by others in the motors 40 + year history.

 

[Nicko]

Thanks again for the great advice, will probably get the top of the barrel skimmed 0.25mm so all will be flat again, I like the idea about a thicker base gasket ( or could I double up using 2 standard base gaskets) this would alleviate the cam timing and piston to head clearance problem.
the location bush was fitted, but the head gasket was blown there, I believe this caused the marking.

an update on my other post regarding the crankshaf, I have arranged a courier to collect tomorrow, the engineering company will fit new rods, bearings and then dynamically balance.

I have taken Raymonds advice and will just add to this post regarding todays niggle, I believe it’s called the input shaft, the smallest gear adjacent to the large bearing is showing signs of longtitudal scarring(no chips) this may be normal and ok to leave, but thought it best to check first, unfortunately it’s the one which is also part of the shaft.
I have attached a couple of pictures below

 

[mike in idaho]

Looks like it's starting to wear through the hard facing, how does the gear on the other shaft look?

 

[Nicko]

Just had a look at the mating large gear and it’s in good condition, the only observation is that you can move the large gear a fraction along the shaft, no rock on it just the tiny sideways movement.

 

[Jim]

I'd replace it. You don't want to be a hundred miles from home... enjoying the ride.... with that little niggle just in the back of your mind.

Speaking for myself of course. I know it'd be in the back of mine.

 

[Signal]

My thoughts on your crankshaft rebuild. Dynamically balancing these cranks is a time consuming and expensive job and for not much benefit. Having the crank trued as near to perfect is a better use of a rebuild budget in my opinion.

 

[JJames]

Thanks again for the great advice, will probably get the top of the barrel skimmed 0.25mm so all will be flat again, I like the idea about a thicker base gasket ( or could I double up using 2 standard base gaskets) this would alleviate the cam timing and piston to head clearance problem.

Thicker base gasket sounds like the ticket if on can be found. I generally avoid double gaskets.