Ridge in cylinder bore

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Dayknight-VW
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Ridge in cylinder bore

Post by Dayknight-VW »

Howsit guys… looking for some advice.. so I’m doing rings on another motor of mine… car was building up excessive pressure in the sump, throwing out through the breather and all seals. The 2nd 3rd and 4th cylinders have ridges on the top of them, basically at the point of where the piston ring stops. The ridge is on one side, on the back of the motor towards the firewall, kind of like un even piston wear. Bearing also had scoring in them but crank looks ok and feels ok.

I know this is not an ideal circumstance, I do understand the effect of ring clearances and stuff but if I hone the bore and put in a set of new rings will this car possibly behave? It’s a spare run around car, not really going to be doing a lot of millage. Don’t want to spend to much on it.
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missioner
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Re: Ridge in cylinder bore

Post by missioner »

For safety sake get the cylinders measured.

The symptoms were sump pressure which is caused by the rings not sealing properly. Simply replacing the rings will not help that much or for very long. This is something I think you know already, otherwise you wouldn't be needing advice.

The possibility that the cylinders are oval and slightly tapered is high in your case. Piston rings are not designed to accommodate for changes in cylinder dimensions, a simple hone won't do much to rectify the original issue either.

If the block is already out of the car, the additional expense to have it bored to the next size up is not that bad in the greater scheme of things. One tip I will give is to buy the pistons first and take one with to the engineers, that's if you decide to go all in and rebore.

I would also suggest checking the valve guides. Rock the valves back and forth when the valve is fully open, more than a millimeter of movement is too much. Worn guides will let oil pass the valve stem seals and add to the smoking problem.

TL;DR I say do it right the first time. Who knows if the spare car suddenly becomes the main car for some unforeseen reason? We live in less than certain times. Besides that a good engine rebuild will also help the car hold its resale value, it's much harder to sell a smokey jalopy than a old well cared for car.

Sent from my Redmi Note 4 using Tapatalk

'87 Golf 1 Olde Skewl OEM+
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Jetta2
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Re: Ridge in cylinder bore

Post by Jetta2 »

What missioner said.

And to add: I have seen motors with bore ridges break brand new piston rings, even after been honed properly. Those ridges may seem small, but they can cause big issues.

Rather get the bores measured instead of risking rebuilding the motor twice.
Ryan Demoser

1996 Mk3 Golf VR6
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Dayknight-VW
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Re: Ridge in cylinder bore

Post by Dayknight-VW »

Thanks guys much appreciated
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