Club 80-90 Forums

That's great,I'll try and double check the other measurement tomorrow too.

Its most likely to be either a rust line (engine standing with inlet valve open and a coolant leak) or a frost crack (if it coincides with the bottom of the skirt where it plugs into the case)
I might just have a couple of used 94.5 barrels kicking around.

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Interesting suggestions. The engine was bone dry when I bought it, had been stood for a number of years.

I don't know if you have seen the pictures a couple of pages back, this is what it looked like before honing, right in the middle of the bore, not concentric. This barrel had a broken no 2 compression ring.

I'll finish off the "honing" and see where things are, I might be very interested in one of your 94.5mm barrels

My initial thought was an inclusion type of defect in the liner steel/material.

Maybe the barrel was bored out to 94.5 at a previous rebuild and the mark is the result of a mishap when machining.

Gave it another little dose of honing this afternoon.

It's barely noticeable to the naked eye, and if you load the full resolution picture you can see I'm at the point where parts of the gouge have been eliminated. What's left is perhaps not much deeper that the honing hatch marks.

I measured the bore and it's now at 94.54mm.

Just need to weigh up if I should continue the hone to eliminate the mark completely and make it a 100% quality bore at the expense of component life, or use it as is, knowing that the barrel will improve as it wears.

Any views ?

I also measured the barrel where it goes into the head - 106.33mm for me with vernier

I thought these barrels must be replaced not honed if there's a problem
Or so it's written in the Haynes manual

If the line is level and given the vertical scrape lines above and below, it looks like its a "Bite mark' from a broken ring to me.

footstuck wrote:If the line is level and given the vertical scrape lines above and below, it looks like its a "Bite mark' from a broken ring to me.

Thanks, that's what I thought too, especially as that is the cylinder had the broken ring, though despite searching I haven't been able to find a picture of a similar example. Why do you think the ring bit - Overheating, fault in manufacturing, or something else ? The barrels, pistons and rings all look pretty new and unworn. I wouldn't want it to happen again.

Kev, I haven't got my T25 Haynes handy, but I do have the 412 one. I think the advice being given is that if one barrel is damaged to the point it needs a rebore, you can't simply rebore it ( +0.5 or +1mm) and put a standard piston in, nor can you put just one oversize barrel / piston set in. You can of course just replace a grotty standard barrel with a good one, which is what he says.

The wear limit for the piston / barrel clearance is 0.20mm, (new is 0.025 to 0.036, maths not what is written in Bentley). If you look at the scores on the doors photo a couple of pages back it shows the clearance was 0.04. With the honing I have done it's now 0.05mm so still well in spec. That's my thought process anyway

Ah I think I'm confusing honing and boring

I did some more honing tonight.

It's slow work. Every 6-7 minutes I clean the oil off the bore to see if the scratch has gone. It's only when I wash the bore down that the scratches become visible again, and only in the "right" light. We're now at ~ 94.545mm