QMB139 Assembly Problem By chatteryteeth (Read 525 times)

[chatteryteeth]

I'm installing a 50mm big bore kit on a QMB139. This is the second one I've done. For some reason I can't get the new jug to seat all the way against the crankcase or "block", whatever you want to call it.

I don't want to send anyone down misleading paths, but I think that the bottom right dowel or spacer thing doesn't sit all the way down in it's spot. I removed that crankcase stud to see if I could see anything. The dowel still seems like it doesn't sit quite as far into the crankcase like the upper one does. When I removed the original jug, that dowel had to be removed with pliers, it was thoroughly stuck. It's making me think that maybe they had this same problem when assembling the original jug and "fixed" it by just torquing the hell out of the four nuts on top of the rocker assembly.

Anyone have any insight or words of wisdom? This has accelerated my balding process by at least half a decade already.










Thanks in advance.

[trashtruck12172]

alot of times it's just cheap chinese machining. if it were german I'd say use a bigger hammer.

[cyborg]

Do all the studs screw into the block the same distance?,,, the threading may not deep enough

[chatteryteeth]

May 20, 2016 17:24:21 GMT -6 trashtruck12172 said:

alot of times it's just cheap chinese machining. if it were german I'd say use a bigger hammer.

So is that what you recommend, just using a rubber mallet or something to force it to seat all the way? I really wanted to avoid "fixing" it by just beating on it, but if that's what needs to be done lord knows I'm about ready to take some frustration out on it...

Thank you for your response.

[chatteryteeth]

May 20, 2016 17:40:15 GMT -6 cyborg said:

Do all the studs screw into the block the same distance?,,, the threading may not deep enough

They seem to, yes. It's only the dowel that doesn't seem to sit as far down. I'd say it's roughly 2mm further out than the top dowel, but it's sort of hard to measure given its location.

[cyborg]

I'd counter bore that dowel hole deeper on the head side,,,I wouldn't force it

[olivertwisted]

I would also be inclined to remove the dowel and check those internal threads with a TAP since, you said that the one that came out was stuck in there. Maybe cross threaded or a burr in there ?