Reboring one cylinder?

cmjones01 · Dec 9, 2013

My Defender 110 is suffering with a broken engine at the moment - see this thread for the gory details. Anyhow, it seems that one cylinder is badly scored and I'm trying to work out what to do. Replacing the whole engine is the obvious choice, but a new one is expensive and a good secondhand one might take lot of patience to find.

My current though is: is it possible to re-bore a single cylinder in an engine block without removing the engine from the vehicle? This might sound daft, but I'm looking for a reasonably quick and cheap repair. Don't laugh too much

Thanks
Chris

Tuskenraider · Dec 9, 2013

No as it needs to go on a boring machine plus doing one cylinder is a stupid idea

Thor1950 · Dec 9, 2013

have a rebore on all cylinders and over size pistons and rings fitted. If it is with in .005 of original you can just have it bored and just over size rings. Thing needs to be balanced meaning you can not just do 1 hole all 4/5 need to be done.

divie · Dec 9, 2013

It used to be possible to do with engine in situ, however it has been a long time since I saw a "Van Norman" boring set up used anywhere. Pull the lump out and get it bored at around £150 plus a set of pistons, and yes do all of them.

jamesmartin · Dec 9, 2013

depending on damage either get it rebored properly to new piston size, or try honing no 4 bore see what it comes up like

pressbrake · Dec 9, 2013

yes you can, but swarf is a pest.I still have a boring bar somewhere but only did big engines in situ

easye1 · Dec 9, 2013

jamesmartin said:
depending on damage either get it rebored properly to new piston size, or try honing no 4 bore see what it comes up like

good idea james, yes it may only need 4or5 thou to get through scoring, but that delapena honing fluid if used will carry many bits of fine particles into the below crank areas.
might just work though after carefull cleaning.
do they do +.005 up pistons?
could always take out a good piston and match weigh the pair, with fettling any extra off the new one to keep all 4 in balance

its not a racing engine is it

minimole23 · Dec 9, 2013

Just do the job properly, a new set of pistons and a rebore is not exactly costly.

Edit, looking at the picture it may clean up with a hone, but the piston may well be toast looking at the pick up. Someone might have a piston lying round, so a new set of rings and you could be good to go. But I would give the engine a freshen up of bearings and rings while its apart.

Thor1950 · Dec 9, 2013

minimole23 said:
Just do the job properly, a new set of pistons and a rebore is not exactly costly.

Edit, looking at the picture it may clean up with a hone, but the piston may well be toast looking at the pick up. Someone might have a piston lying round, so a new set of rings and you could be good to go. But I would give the engine a freshen up of bearings and rings while its apart.

+1 a good hone& some measurements for taper or out of round might get away with that and +.005 piston rings. After hone check end gap is with in tolerance

divie · Dec 9, 2013

Pistons are cheap for standard motors like that. I have a 1919 Castle car with a Dormon engine. Did not want the ball ache of finding a piston similar and altering to suit so I gave the bottom of the pistons a light knurl in the lathe and turned to suit the bore. New rings and it runs well. No need for you to codge like that though.

cmjones01 · Dec 10, 2013

Thanks for all the thoughts and advice - it's taught me a lot about engine reboring! If only I had the vehicle in my own garage and had the time to work through the job properly, I'd love to strip down the engine, get the block rebored, and rebuild it in my own time and know the job was up to scratch. Sadly it's in a commercial garage, the depths of the Polish winter are approaching, and I'd like it to be back on the road as soon as possible (and so would my wife!)

What all this tells me is that there are really no short cuts - it's either a full rebuild or a replacement engine. I think looking for a secondhand replacement is probably the way forward for now, much as I'd like it to be otherwise.

Cheers
Chris

easye1 · Dec 10, 2013

divie said:
Pistons are cheap for standard motors like that. I have a 1919 Castle car with a Dormon engine. Did not want the ball ache of finding a piston similar and altering to suit so I gave the bottom of the pistons a light knurl in the lathe and turned to suit the bore. New rings and it runs well. No need for you to codge like that though.

good trick - old dodge though.
next time, turn it "round" to your diameter, then fettle a few though extra from the sides.
the knerling will hold the oil better thus reducing more wear anyway.

hand on heart, my old long gone dad told me he once had an arial square 4 motorcycle, but it had a broken piston,
not much chance of getting one piston easily,
so he made one from the hardest wood he could find

put ring grooves in, put it back together, and it ran....

so he sold it quick.....

must have been in the 1950`s....lol

MGBGTV8 · Dec 11, 2013

Tuskenraider said:
No as it needs to go on a boring machine plus doing one cylinder is a stupid idea

It certainly can be done!

It was certainly done on one of the world land speed record cars according to Nigel Thornleys book "maintaining the breed".

Can you guess what my current "thone material" is this month? lol!

easye1 · Dec 11, 2013

I knew a racer friend of mine who when visited one night, was boring an mgb block out to take some lotus type pistons. true the block was on the workshop floor, but the boring machine just bolted to the top of the block.
had to offset the middle two bores or they would have met

but bored them to accept "wet" liners as the diameters encrouched in waterways,
used a BMC diesel crank, offset ground on the big ends giving longer stroke, used rare BMC/MGA twin cam conrods, a hand made copper head gaskit, and it ran very well.

came out roughly two and half litres.
our then limit on stock car engines was just the 1800 MBG block +.060....lol

tricks of the trade to win at any cost.

hw now runs a business selling & racing USA style sprint cars with chevy V8`s, but all the engines come with a anti tamper seal..
(wonder who puts the seal on...just thinking out loud vince

.. )
lol

SteNova · Dec 11, 2013

go for it, I honed a bore and fitted a single odd piston when I melted one on my nova

pressbrake · Dec 11, 2013

MGBGTV8 said:
It certainly can be done!

It was certainly done on one of the world land speed record cars according to Nigel Thornleys book "maintaining the breed".

Can you guess what my current "thone material" is this month? lol!

I have done plenty single cylinder bores in situ, then honing the last couple of thou to size

Reboring one cylinder?

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