Where to take barrells for rebore and advice

[surfer]

Help. Anyone know any good engineering shops on the North shore to take my barrells in for some advice?

Or the answer to this:

I have a 1981 Yamaha XS650SH. Inside one of the barrells about two thirds of the way down there is a horizontal groove that runs halfway around the barrell. The groove is below the rings when the piston is at its lowest point. But above the bottom of the piston at its lowest point.

Is this coincidence? The barrell with the groove is the same side as a broken big end bearing on the crankshaft. The broken big end bearing caused the piston to travel further up the barrell and smack into the inlet and outlet valves on that side. (Cheers to Andrew at motorcycle graveyard, I now have a new crankshaft fitted. The valves are both ok).

Will the groove be a weak point in the barrell which may at some stage break off? Or has it affected the piston travel and as a conseqeunce gouged a groove out of the barrell?

Cheers

[ManDownUnder]

Sounds like you have it in bits - and if you do then pics might help?

An experienced eye in these parts might also be available (not mine but if you are able to transport said machinery...?)

Offhand I'd say it sounds ok so long as the rings don't catch or foul on the groove, and there is no material from that groove sticking out into the cylinder to foul on the skirt of the piston.

Walls of the cylinder block are reasonably thick but then I have no idea how deep the groove is... and "no groove" is obviously better than "having a groove".

[more_fasterer]

Take it to Engine Specialties, 96 Hillside Rd Glenfield, 489 4806.

[surfer]

Thanks for the quick replies.

The groove on the inside of the barrell is hard to get a good shot off. This is looking down the barrell from the top. The groove is about one third of the way down at the front of the inside of the barrell.

Cheers

[JMemonic]

It looks like the bottom of the ring travel from the photo, get the piston and bore measured, and see how it is for tolerances.

[vagrant]

Take it to Engine Specialties, 96 Hillside Rd Glenfield, 489 4806.

Yup, these guys. They did the rebore on my RC30. Was a prick to set up, being a tiny V block.
They did a great job considering the piston to bore clearance is set at 0.0005"
Not a mistype, 1/2 a thou is what the book calls for.

So, they do pretty good work!!

[surfer]

Thanks for the quick replies.

The groove on the inside of the barrell is hard to get a good shot off. This is looking down the barrell from the top. The groove is about one third of the way down at the front of the inside of the barrell.

Cheers

Ooops should read two thirds from the top not one.

It looks like the bottom of the ring travel from the photo, get the piston and bore measured, and see how it is for tolerances.

Yep, I measured with a tape measure and the groove is below the piston rings given the travel for the piston, not sure about the bottom of the piston though. Having said this the groove does not fit the shape of the piston either. But it is an interesting one to find out. I will put up a post and let you know.

[JMemonic]

Yep, I measured with a tape measure and the groove is below the piston rings given the travel for the piston, not sure about the bottom of the piston though. Having said this the groove does not fit the shape of the piston either. But it is an interesting one to find out. I will put up a post and let you know.

Why I suggest it is the bottom of the ring travel is the fact below the grove appears to show hone marks these are marks that appear horizontal, above that appears to show vertical lines, I suspect that if the bores are measured they will be well out of round, I would almost lay money on the grove being on the thrust side of the piston.

[Pussy]

Hey, surfer. The automotive machinists at Taumarunui are the people you're after. A bloke called Ray Nielson used to own the business, and it is now owned by a bloke called Dave West (westicals !!). Both of these guys are true craftsmen. I have seen them do all sorts of re-sleaving and obscure modifications

[surfer]

I took the barrel into the local place near me, Engine Specialties. They reckon the groove is a machinists error in setting up for a rebore when the barrel was rebored.

They are measuring the pistons and barrels for me though.

The groove is on the thrust side of the piston but it is not the same shape as the bottom of the piston. The piston and barrel seem to have suffered a lot of wear probably due to someone previously running the bike without changing the oil. This would also account for the damage to the crankshaft.