Engine cases bore diameter

gday Hacker,

yes I find this as well, I think it is only worth measuring the ovality (out of round) of the liner if it is in the cases and even then probably only at operating temp with the head bolted down which isn't completely possible

bushmechanic said:

Hi Dave

i use about 1-2 ton with the liner in the cases at a guess, its quite a lot but when supported there is no problem.. well so far

what i did was use an internal mic to measure how much deflection i put on the liner.. (approx 5mm at first but 10 is needed sometimes)

took it all apart and measured the out of round, if it needed more then I knew how much to deflect it next time

if you got a holesaw or treppaning tool and cut a hole in a series of 20mm structutal plywood blocks or even better some alloy plate about 120mm square you could pin or glue them and use those to put the liner in while squashing it... less chance of breakage that way.

IMHO though there really isn't much point measuring the liner if it isn't in the cases, to be more accurate they would have to be at operating temp

Click to expand...

http://husaberg.org/mechanical/17147-05-650-piston-diameter-measurement.html

My cases have always come out being out of round and the liners won’t turn freely till I correct the localised deformation of the cases near the joins and squash them overall back into round in my press. I really need to get a mill so I can machine this sort of problem out.

Click to expand...

the HBERG case ovality thing probaby doesn't matter that much as its surely some weird shape when its hot anyway. It worries me though because ive seen a 550 engine rip the nikasil off the liner front and back at 20 hrs, cases were ovalised about 0.2mm out of round.

Click to expand...

http://husaberg.org/mechanical/11677-jbs-700-kit-welded-80mm-crank.html

Is it possible to strenghten cases in some way to keep their nominal shape&size?

Hi hacker

it is probably "normal" i mean how many people would bother to check it ?

but it is definitely not good so yes do something.

first I measure the liner, mine has always been round.

then I put the liner in the cases then tighten the case bolts

measure out of round of the liner as installed

if the liner was OK in step 1 take it out or if it was not round in step 1 leave it in.

squash the cases in a press till the case bore or the liner measures correct.

if you took the liner out, put it back in and check

I use some soft wooden blocks to support the cases and also one on top to spread the load from the press.

I don't think it would be practical to strengthen the cases tovias, but it would be very interesting, some steel bits and threaded rod or something.

It may be worthwhile re machining the case bore instead of bending the cases because my cases at least seem to have found a place where they are happy. I keep bending them and they keep bending back.

so instead of bending them you could machine the bore again. would need a very very careful setup.

I think I would put some bearing blue on the liner`s contact areas
bolt the cases around it, disassemble and check for hard spots.
the tight spots could be releaved by polishing carefully with emery
and a stick, repeat until liner can just spin.
At least that is what I would do, short of boring it round on a mill.

good tips spanner

I also found localized deformation at the junction between the 2 case halves, like they get squashed, fixed it with a file

only found it trying to get the JBS liner to rotate freely

For some added entertainment,put the bore guage in the cylinder liner,sqeeze the liner with your hand and watch the needle move.

yes I have seen this many times. I have them bored out together. if we take more than a 'little' we have to go to larger O rings to keep a seal. the problem is that you must then go to a size that suits the new O rings....

It is also possible to "un-oval" the liner from its precarious state!

regards

Taffy