Cylinder Wall Ridge Help

[MrMuddle]

Hi All, looking for some advice please. I've started the strip down of my engine and replacement block, new block is M50B25 and I'm swapping in my M52B28 internals. First issue I've encountered is there is a small ridge at the top of each cylinder wall which you can feel with your finger nail.

I've had a look online and have seen that some people use a Ridge Reamer to remove this ridge, then hone the block. My question is, does anyone have experience of this and is it safe to remove the ridge using a ridge reamer, hone the block and then use the stock M52B28 pistons and rings?

I've spoken to a few engine shops and they're telling me I'd need to bore out the cylinders and then use oversized pistons which I really can't afford tbh!

I've compared the M50B25 pistons and M52B28 pistons and the top ring is slightly higher on the M52B28 pistons, so it looks like the top ring will foul the ridge if its not removed!

Any advice would be gratefully received.

Thanks very much
Rob

Sorry I forgot to add, this will be a boosted engine.

[someguy2800]

It is pretty normal to have a ridge like that in m50's. That is not what a ridge reamer is for. You cannot hone it oversize without new pistons or the piston to wall clearance will be excessive. According to my measurements m50 vanos pistons have a top ring land thickness of .347" and an m52 is .327". However in stock form m52 pistons sit .055" below the deck at top dead center the rings will be .035" lower in the bore and it will not overrun the ridge.

[Butters Stoch]

You can clean it all up with just a ball hone. Start quick, slow it down to get a nice cylinder wall.

Sent from my E6782 using Tapatalk

[someguy2800]

That corrects the cylinder finish but does not fix the geometry of the cylinder. Ball honing is a good idea for the new rings to seat though. As long as the rings don't run over the top of the ridge it will be okay.

[MrMuddle]

Thanks very much for the replies both, that's really helpful. Could I use a torque plate and then hone out the cylinders to remove the ridge, would that provide a better finish?

Is the full height of the M50 block the same as the M52, I assume it is and it's only the internals that are different? Sounds like it would be worth me mocking up the M52B28 crank, maybe two rods and pistons with old rings and see if at TDC they reach the ridge, if they don't then just hone the block as normal and hopefully be ok.

I've no experience of engine building so excuse any stupid questions!

Another thought I had was, could I swap the M50B25 pistons over onto the M52B28 rods so the top ring was lower? Or would that not work because the M52 crank and road would result in the M50 piston sitting at a different height?

[gdavid]

If the compression ring doesn't travel that high, you have no problem, ball hone will improve the rest of the cylinder wall and should be done but leave the ridge alone. Test assemble the bearings, crank, one rod and piston without rings to verify but if someguy2800 believes it will stay lower, I would wager on it.
I am putting a m54b30 rotating assembly in a m52b25 and the compression ring does come higher than the original ring did. I went at it with a 3 stone hone, which is probably risky but I do not have the budget for custom pistons. There is still a difference in color at the top of the cylinder but you cannot feel it. I am still anxious about it and will be going easy on the engine during break in. I figure, if I break a ring gland, I will over bore at that point and s52 (us obviously) standard bore pistons will be cheaper than cheaper custom any size.

[someguy2800]

Thanks very much for the replies both, that's really helpful. Could I use a torque plate and then hone out the cylinders to remove the ridge, would that provide a better finish?

Is the full height of the M50 block the same as the M52, I assume it is and it's only the internals that are different? Sounds like it would be worth me mocking up the M52B28 crank, maybe two rods and pistons with old rings and see if at TDC they reach the ridge, if they don't then just hone the block as normal and hopefully be ok.

I've no experience of engine building so excuse any stupid questions!

Another thought I had was, could I swap the M50B25 pistons over onto the M52B28 rods so the top ring was lower? Or would that not work because the M52 crank and road would result in the M50 piston sitting at a different height?

A torque plate is only useful when using a rigid hone such as what they use in engine machine shops. A rigid hone does not conform to the cylinder so it hones off the high spots and leaves the low spots. A ball hone does conform to the cylinder so a torque plate does not help anything and it will remove the same amount of material from within the ridge as it does everywhere else. A ball hone is only for improving cylinder finish, it is not for fixing out of round in the cylinder.

The deck height is 210mm and a 1.75mm head gasket. The M54 is a 211mm deck height but only a .75mm head gasket so even they work out to be the same.

You technically could use m50 vanos pistons with an m52 crank and 135mm rods. If you work out the stroke and rod length the pistons would sit .5mm lower in the bore than original, but because of the increased swept volume the compression ratio would be increased to about 11.3:1 which is not a good plan without alcohol. Your best bet is a complete m52 rotating assembly. It will be just fine, no part of the piston or rod will touch the ridge. If you want me to double check just measure the pin height of the m50 and m52 pistons and I'll do the math.

Here are some specs if you are interested

https://www.bimmerforums.com/forum/s...a-9-inch/page2

[someguy2800]

By the way the actual purpose of a ridge reamer is actually to just remove the carbon ring at the top of the cylinder so you can get the pistons in and out again without breaking piston rings. They are not meant to correct cylinder geometry and if you use one to cut into the cylinder wall enough to remove the ridge you are actually just making things worse since you are increasing the bore size at the top of the ring travel. This will force the whole ring to travel in and out of the ring land on every stroke and that is not helpful for anything. Same think you could hone out the ridge in a rigid hone but that will increase the ring end gaps and piston to cylinder wall clearance to unacceptable levels. The only thing you can do is run a piston with a lower ring height relative to the centerline of the pin, or bore the cylinder oversize and get new pistons.

Anyway, put the m52 pistons and rods in it with the m52 crank. It will be fine.

[MrMuddle]

Thanks very much, that's really helpful. We've checked my mates engine who's doing the same build and it looks like the top piston ring on the M52 setup comes up to just shy of the bottom of the ridge. I'm going to check mine this week as well in case there's any difference, but it looks good.

Thanks very much again for all the help.

[Corky325]

I just had this problem on my m50 and here are my thoughts:
If there is a ridge on the cylinder wall this is due to excessive wear of the cylinder wall (by the piston rings i think). This results in a oval bore in the top portion of the piston. The oval portion of the cylinder willhave a larger circomfrance. This larger circomfrance will make it hard to gap the rings as it will very greatly from the top of the bore to the bottom. It is also a lot harder for the ring to seal an oval bore.

So in general i think it is a bad idea to run the block with a stock sized piston, it should be bored oversize (85mm).

[hsvturbo]

You can clean it all up with just a ball hone. Start quick, slow it down to get a nice cylinder wall.

Sent from my E6782 using Tapatalk

is that a gouge next to the alignment dowel and cylinder?


SG2800,

did I read somewhere on this forum that you could bore out a engine 0.5mm for oversized Pistons? If so, what was your method? Thanks..

[someguy2800]

SG2800,

did I read somewhere on this forum that you could bore out a engine 0.5mm for oversized Pistons? If so, what was your method? Thanks..

Its not a do it yourself job but it's a simple and routine procedure for an engine machine shop. It must be bored out with a boring bar and then honed to size on a rigid hone.

For my motor I just found a block with only about .0005" ring wear and then ball honed it at home and ordered stock bore wiseco pistons.

- - - Updated - - -

I just had this problem on my m50 and here are my thoughts:
If there is a ridge on the cylinder wall this is due to excessive wear of the cylinder wall (by the piston rings i think). This results in a oval bore in the top portion of the piston. The oval portion of the cylinder willhave a larger circomfrance. This larger circomfrance will make it hard to gap the rings as it will very greatly from the top of the bore to the bottom. It is also a lot harder for the ring to seal an oval bore.

So in general i think it is a bad idea to run the block with a stock sized piston, it should be bored oversize (85mm).

It is in fact the rings that wear out the cylinder. M50 vanos and newer blocks have chrome faced rings that wear the cylinders a lot. The ring wear does not really affect the cylinder seal that much until it gets over about .003" or so. The rings are flexible and easily conform to that much out of round. Most of the wear is in the top inch of ring travel on the thrust sides of the bore. Pretty much all the used block you will find with chrome rings will have this wear.

[Corky325]

It is in fact the rings that wear out the cylinder. M50 vanos and newer blocks have chrome faced rings that wear the cylinders a lot. The ring wear does not really affect the cylinder seal that much until it gets over about .003" or so. The rings are flexible and easily conform to that much out of round. Most of the wear is in the top inch of ring travel on the thrust sides of the bore. Pretty much all the used block you will find with chrome rings will have this wear.

My ring gap changed by .010" ftom the top of the bore to the middle, so i guess i would just check the ring gap change and it should give you an idea of where the bore size is at.

[someguy2800]

My ring gap changed by .010" ftom the top of the bore to the middle, so i guess i would just check the ring gap change and it should give you an idea of where the bore size is at.

https://www.ebay.com/sch/i.html?_fro...gauge&_sacat=0

[Corky325]

https://www.ebay.com/sch/i.html?_fro...gauge&_sacat=0

Lol, i dont use one enough to justify it, but (ring gap variance)/pi will asicly get you what you need.