engine building question - ring gap and piston wall clearance

[cpalella]

First off, this is not a FI related question (engine is NA) but it seems there is a good concentration of technical knowledge for engine building in this subforum via some very accomplished and knowledgeable BMW enthusiasts. So please excuse my NA intrusion into the FI subforum....

Here is the situation. I am doing a mild restomod with the first car I ever bought. 1996 328 convertible. Bought it with lawn mowing money I saved from the time I was 11. Sentimental value is high with this one. I want the car to be my daily when it's done. The motor had about 100k on it but was leaking from literally every sealing surface so I planned to take it to the short block, check clearances, and then regasket and call it a day. I pulled the head and there was some light surface rust in a few cylinders (the engine sat for about a year out of the car before I opened it up or turned it or anything...). This prompted me to just tear the whole thing down. Main bearings looked like new (and clearances were perfect) so I'm reusing them. Rod bearings were bad (a few showed copper) so those will be replaced... good thing I opened it up....

After cleaning and checking the deck for straightness (it was absolutely perfect) I used a ball hone/dingle berry/flex hone to resurface the cylinders for new rings. Followed the instructions etc. Went to start gapping the new rings (goetze brand) and I am getting some relatively large ring end gaps According to the BMW TIS the top ring end gap should be between .1 mm (.0039") and .3 mm (.0118"). I am seeing somewhere between .35 mm (.0137") and .45mm (.0177"). I am measuring ring gap at the bottom of the cylinder down below the normal wear path of the piston/rings.

My question is twofold. Should I be worried about these end gaps being slightly out of BMW specs? And how/why am I getting an end gap outside BMW spec when I'm using OEM rings and placing the ring low in the cylinder where theoretically the cylinder shouldn't even be worn? I'm a little stumped and frustrated. Or am I fine and I'm just overthinking this and paranoid?

And to clarify, this is a 2.8 M52 block with 84mm (3.307") bore. I do have a dial bore gauge and measured the bore to be about 84.19mm (the TIS allows a +/- .1mm on bore size). I want to measure it again anyway.

I also maybe got a little crazy and pissed off and went to the junkyard and pulled a low mile 2.3 for the block and head over the weekend because I was convinced my block had been slightly overbored... pulled the head, cleaned a cylinder and dropped a ring in it and still got about the same end gap as I was already getting, just slightly tighter. maybe .03mm better.

I did find a hastings instruction manual which gave an end gap range of .010"-.020" placing my measurements within their specs albeit on the looser side.
https://www.hastingspistonrings.com/...sion-ring-gaps


Here's a photo of the engine block to catch your attention, the e36 is in the background

[someguy2800]

M52's used chrome rings which wear the bore quite a bit at the top of the ring travel. You will usually be able to feel a ridge about 3/8" down from the top of the bore, especially on the right and left side of the block. This is normal and bore wear in this area is pretty common to be .1mm or so on higher mileage blocks. Its not ideal but it will be fine and pretty much all the used blocks you'll find will be this way.

Second I don't know what they are smoking with the spec of "BMW TIS the top ring end gap should be between .1 mm (.0039") and .3 mm (.0118")" But those are totally absurd numbers. If you put a motor together with .004" ring gap you wouldn't make it around the block without cracking all the ring lands. No bmw I have ever take apart had a ring gap this small. A normal spec for that bore size on an NA motor is .014" top and .017" 2nd.

[cpalella]

M52's used chrome rings which wear the bore quite a bit at the top of the ring travel. You will usually be able to feel a ridge about 3/8" down from the top of the bore, especially on the right and left side of the block. This is normal and bore wear in this area is pretty common to be .1mm or so on higher mileage blocks. Its not ideal but it will be fine and pretty much all the used blocks you'll find will be this way.

Second I don't know what they are smoking with the spec of "BMW TIS the top ring end gap should be between .1 mm (.0039") and .3 mm (.0118")" But those are totally absurd numbers. If you put a motor together with .004" ring gap you wouldn't make it around the block without cracking all the ring lands. No bmw I have ever take apart had a ring gap this small. A normal spec for that bore size on an NA motor is .014" top and .017" 2nd.

Thanks for the feedback. Really appreciate it. I felt that ridge at the top of the bore

Glad to know those gaps are too small. I started gapping rings again last night. Best I could come up with after swapping them around for best fit were somewhere between .015 and .017 top ring. Second ring came out about the same. I guess it's not ideal but its also not a track car trying to make some NA record for used m52 on stock ecu, stock rings, stock CR, stock pistons etc. I'll just send it