krombacher

I was reading up on cylinder scoring, and came across a document by Hartech, which listed out quite a list of contributing factors. Apparently the scoring is much more likely to occur on thrust face in the cylinder where there is no oil being squirted.

Have you heard of anyone modifying the oil squirters just on bank 2, so they spray more oil on the cylinder wall that primarily get's scored (the thrust side)? See Bank 2, Point A, on the diagram in PDF pg 23 on -
http://www.hartech.org/images/downlo...0(interim).pdf

dporto

Wow... So much info there. They've clearly done a lot of work/development on these motors. Not only will it take a while to read, but comprehension/retention is difficult without some hands on technical background. I'd love to hear some comments from other developers/mechanics (not snarky stuff) who are able to contrast and compare with their own experiences/findings.

Schnell Gelb

Probably better to chamfer the the big ends.
Check the oil squirters are clear when rebuilding.Lots an lots of cleaning flushing, ultrasonic

krombacher

Great link SchnellGelb. That makes sense.
Does any of the engine builders out there have any comments on chamfering the big ends to improve oil flow this way vs redirecting the oil squirters to the thrust side of bank 2, on the m96/m97 engines?

Also, as a backgrounder for others, I found a great and relatively short video on basic engine lubrication systems, showing how oil moves through the crankshaft and bearings, wet and dry sump systems, and oil squirters. In their example they show a dual jetted piston squirter, where ours has just one.

See Hartech's pdf link from the original post for a diagram of our exact configuration (pdf Pg 23).

I suppose replacing the Pistons (with fresh low-friction coated piston skirts) and replacing worn bearings (improving oil pressure) would help, as well as installing an external oil cooler (maybe with a fan) would also help. Or are these part replacements generally sufficient to keep he cylinder walls from scoring again? (At least until hey wear down again).

mikeborden

I think that's the old guide, which needs to be updated. Baz has mentioned that a couple of times on the UK board. One of the things he has mentioned in a couple of other threads is that pointing the squirters to better lubricate that side didn't help. So, while making sure you get lubrication in the cylinders is a good thing, don't bust your *** trying something different to resolve the scoring problem.

It's one of those deals that there's a bunch conflicting theories as to why it happens.

Mike

Macster

The piston oil squirter system consumes a considerable amount of the engine's oil budget. In one case the oil pump's output is 65 liters per minute. Of this the oil jets are claimed to consume 17 liters per minute. That's a lot of oil.

The oil supplied by the oil jet is claimed -- this by Porsche -- to keep the piston 50C cooler than it woudl be otherwise.

Aim the oil jet to spray oil more to one side and the piston could run considerably hotter. While the thrust side of the piston might be better lubed -- though this is not a guaranteed benefit -- the piston crown and area above the rings could run substantially hotter with likely disasterous results.

Might point out the oil being sprayed at the bottom of the piston can flow out through the oil control ring holes and thus to the piston/cylinder wall interface.

There is plenty of oil being supplied to the rings/piston and cylinder walls.

What is probably going on is the old bugaboo of quality assurance. Some oil jets may not flow as much oil as they nominally should due to quality control or possibly contamination. I recall in one case an owner tore down his engine that had experienced some kind of failure with a cylinder and found a metal shard stuck in an oil jet which had apparently reduced oil flow through the jet thus the piston/cylinder ran hotter than the others and hotter than it should and suffered the consequences.

Schnell Gelb

The M96 is probably not the best engine for the diy people (me) to experiment with ?
If this was a small block Chevrolet ,there would be lots of detail on such a subject so you could confidently make intelligent mods. M96 , not so much.

Macster

Chamfering crank journal and rod journal oil holes is probably ok. One doesn't want to go overboard with the chamfering though.

The book: Porsche 911 Performance Handbook has some good info for engine DIY stuff though the info is not directly for the 996 engine.

Agree with you regarding the small block Chevy (or Ford or Dodge) engine and the amount of detail there is for DIY engine rebuilders. Been a while since I followed the small block stuff but used to be almost every issue of brand specific engine magazine there would be an article or two on engine building or engine mods and dyno testing. All great reading.

Heck, I remember years ago there was a lot of info believe it or not the 1600CC engine in my Datsun 510. Low end and top end info and intake and exhaust. I used the info to rebuild an engine, fitting 0.030" over 240Z engine pistons to it for the bump in compression ratio. The info for the top end came in handy so I could adjust the valve stem heights so the cam lobes would optimally contact the rocker pads.

Then I used the info on intake mods to add dual side draft Webers to the engine.

Additional info about fuel system came in handy: I blocked off the place the stock fuel pump bolted to the engine and added an electric fuel pump back by the gas tank. Added a quality adjustable fuel pressure regulator too. Put in a nice engine torque strap to keep the engine front twisting on its mounts, too.

Tons of info.

For the 996? Not so much.

Chiamac

Not sure, I think someone who is knowledgeable with engines could learn enough from the info out there and from other opposing engines to make decisions on these engines. Plus, and maybe I'm lucky locally, there are a ton of people out there who know these pretty well, other than almost all of them aren't online - they are busy working in their shops.

Chiamac

Took my Guzzi motorcycle engine and fitted larger valves, with a new cam, and lightened the flywheel by a bit (not swiss cheese but enough). Not much out there specifically in the way we were going, but enough was there to put things together and found a great engine guy in town to do the head work.

Part of it is learning on the fly though and it needs at some point stronger valve springs, and I want to play around with the timing and advance a bit more, maybe even take out the advance all together... Just a fun thing to play with and make noise with if/when the house project let me permit to spend money on something else. Also could use bigger carbs and porting out the heads...

In my mind the only difference between that and a 996 project is size and cost, and resale. But at some point an engine is an engine and a technical person would be able to learn about a new engine enough for them to work on it - or at least in our cases most of the time, bolt on new parts to them and put it back together.

IMO

Flat6 Innovations

Thats the same area that suffers from issues related to piston pin offset.

The issue isn't related to the oil squirters.

Slakker

The best way to learn is through failure, which is great. The problem with the DIY hack jobs is that people get bored and then sell the car without revealing the extent of their experimentation. And it's the next guy that get to find out whether it worked long term or not.

krombacher

I thought for some reason piston offset could reduce friction on the thrust face of a piston.(?)

Flat6 Innovations

It can, if it's correct for the rod angle/ stroke and piston cam skirt profile.

It can also CAUSE issues.

krombacher

Can better Pistons fix it, or is it a crank / cylinder / block un fixable geometry issue?

If Pistons can fix it, Does anyone know who makes Pistons that corrects (?) the piston pin offset issue on the 2nd bank (the side with the major scoring issues)?