Barrels on but pistons won't move, what's going on. Help me !!!

[billdn]

Barrels rebored to +.25 and pistons/rings supplied to suit.Bit of a fight to get barrels on but now pistons won't move up or down when turning crank. Moved fine before barrels went on, stripping back down to look but any ideas,  please help me before I turn to drink !

[Nurse Julie]

They should be tight Bill if the rebore was done to the correct tight tolerances. But, they should move. Did you put any assembly lube (Graphogen or similar) or oil down the bores?

[Nurse Julie]

Another thought Bill, did whom ever do the rebore physically have the new pistons when the work was done?

[Johnwebley]

Check the ring gaps,


Do the pistons move in the bores without the rings?

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[billdn]

They should be tight Bill if the rebore was done to the correct tight tolerances. But, they should move. Did you put any assembly lube (Graphogen or similar) or oil down the bores?

Hi Julie,
Assembly oil galore on pistons and bores.

[billdn]

Another thought Bill, did whom ever do the rebore physically have the new pistons when the work was done?

Julie, yes he had pistons , rings not fitted but then you wouldn't 😉

[billdn]

Check the ring gaps,


Do the pistons move in the bores without the rings?

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Took ages of gentle tapping to remove barrels, so tight and I mean no slide at all.
Chucked the towel in for today, but tomorrow will remove 1piston, measure bore with vernier as best I can   and try piston with no rings, looks like bottom set on 1 are toast anyway.
Cursory measure made with steel rule and barrel diameter looks like 51.5, crude measure I know.
Keep you posted, thanks Julie and John

[Nurse Julie]

Measure the ring end gap Bill whilst the piston/ rings are in the bores. This will tell you quite a bit.

[Johnwebley]

Measure the ring end gap Bill whilst the piston/ rings are in the bores. This will tell you quite a bit.

I suggest you attempt to slide a piston down the bore,

Use the piston to push the loose separate rings down the bore,it will keep the rings square in the bore,


Also,check the depth of the ring grooves, it is a slim chance they're not deep enough, causing the rings to protrude to much.



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[billdn]

That's tomorrow sorted then,
Rings and pistons from DS so should be OK but we've all been there before.

[billdn]

Measure the ring end gap Bill whilst the piston/ rings are in the bores. This will tell you quite a bit.

Dumbo here 🤪 do you mean ring end gap or gap between ring and bore, the latter I guess use feeler gauge but the former I'm not sure 🤔

[Nurse Julie]

https://youtu.be/ViEjQ7B1uM8
The above will give you a good understanding of what you are measuring with the end gap and how to do it Bill.
You don't measure piston/ bore clearance with a feeler gauge, you need a bore gauge to determine the bore measurement accurately. The difference between the skirt measurement of the piston and the bore is the piston / bore clearance. This should be about 1 thou inch maximum clearance. Unless you have measuring equipment with lots of decimal points, you won't get an accurate reading. I'll just have a look in the manual to see what the ring end gap should be as I can't remember.
Edit.... It was easier for me to take a photo.

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[McCabe-Thiele (Ted)]

I assume the new pistons were numbered from when the rings were gapped to each cylinder when it was bored out or have you done that part?

[Oddjob]

Are you sure the rings were fitted the right way up? They are normally marked with a T which goes uppermost.

[Bryanj]

Another possibility is a scraper side rail has twisted, been there