Kevin in Atlanta

I added a smiley face. Are we good now?

Kiln_Red

LOL! Smileys, emojis, and GIFs are the glue holding society together nowadays.

Kevin in Atlanta

So, the upshot from all this is:

.0032-.0011 = .0021 and all my readings above need to reduced by .0021.

KB

Strosek Ultra

The 928 is a German car. Why do you guys not use the metric system when performing measurements on the 928 engine?
All specifications from the factory are according to the metric system.
Kevin you do not need a ring to set the dial gauge. It's okay to
use a micrometer. The same micrometer is also used to measure the piston. The difference is the wall clearance.
Then there is something called error of measurement.
Åke

Kevin in Atlanta

Of course you're right. I have a micrometer. I could have used it.
​​​​​Someone offered to make me a setting ring so it would be a shame not to use it.

The bore gauge was a gift. It came in inches.

​​​​​​Next on to figuring out of if any of the bores are out of spec.

I love learning stuff. Old dog new tricks.

Strosek Ultra

Kevin, I thought it would be easier for you to have measurement tools in metric. If someone made a setting ring for you, the ring must be made with utmost precision. This type of rings are available for purchase in the market.
Many people mistakenly believe that the right piston clearance is of utmost importance. That is wrong, every time you hone a cylinder the piston clearance increases, old pistons are worn with increased piston clearance as a result. The most important thing is that the cylinder is completely round, the second most important thing is that it is straight (no taper). Of course within certain tolerances.
Every piston is made oval and conical. This is to compensate for thermal expansion.
The factory prescribes a piston clearance of 0.024 to 0.048 mm for the 928 engine. Wear limit is said to be about 0.08mm. Even with a larger piston clearance of maybe 0.10 to 0.12 mm, the engine will work well without abnormal oil consumption as long as the cylinders are completely round and have minimum scratches. The disadvantage of large piston clearance is a higher mechanical noice from the engine, a rattling noice from the pistons, especially at cold start.
If the cylinder is honed to a slightly larger dimension, the ring gap increases. A 0.05 mm larger cylinder bore increase the ring gap by 0.15 mm.
Åke

Mrmerlin

I think the thing thats missing in these measurements is finding a way to like other people.

I think that liking another person is a gift thats been taken away from all of us.
As all Humans are given the gift of being good.

When you can find a way to like another person,
then you will find that kindness will resound from your person.

Now thats a gift that money cant buy..
Yet the reward is priceless.

jeff spahn

I actually find the way Greg responds as a fresh breath of unwoke air. I don't get my feeling hurt. Yes I have one and it is thick.

icsamerica

Not in my case. Nothing "un-woke' about lies. His responses to my threads were full of blatant lies, suppositions, scare mongering and demonstrably false information usually followed by some very 'woke like' word-salad back pedaling.

All the self aggrandizement and attempted destruction of others is very woke but the most un-woke and misogynistic thing he actually does do is blame Mary often when someone on here complains about an unfulfilled order or unsatisfactory service.

GregBBRD

Just as a point of order....for anyone trying to learn something about cylinder wear measurements:
You've now posted twice on this thread....with nothing to say about the topic, but only to make personal attacks on me.

At the very least (independent of how I chose to approach it....I live my life , and type what I think, my own way), I did post about the math error that Kevin had made.....right at the very beginning of his calculations, which threw off all the measurements!
Only to try and help him!

And now you have the audacity to post about who is responsible for what tasks, in my own business?
How does that, in any way, involve you?


I fail to see any possible way that you are adding anything, here.....
It's a$$hats (like you), who degrade Rennlist, with the personal attacks!

Bigfoot928

...

Kevin in Atlanta

I tweaked my results. Not posted here yet. One result was .0034 on the number 1 cylinder.

So, if I add .0034 to 100 I get the diameter of the bore is between two points at a specific height in the bore, right?

Then I subtract the tolerance group 1 piston size to get the piston to cylinder wall, right?

Then I compare it to the .0024-.0028 mentioned above.


Am I close?

GregBBRD

Regretfully, I'm forced to bow out of this discussion.
And certainly many future discussions.
Semi retired.
Someone else can play expert, from here on out.

I was never into this entire "Rennlist" thing for abuse...only to try and help people and offer suggestions.
But I've sure gotten a bunch of abuse, stating facts.
Yup, I'm not anywhere close to a "sugar coater" of part of the "woke" movement, but I've never thought that is what people are looking for, on this Forum.
I always thought that people were asking questions for help, not a warm and fuzzy answer.
Facts should be facts. Good information should be good information. Data should be data. Reality should be reality.
And while I've certainly got a bunch of all of the above, tucked away in my head, there seems to be five or six people (including one moderator) that don't want to hear it.
They seem to want to be the person with lots of knowledge...or promote someone else to be the expert.

Fortunately, for everyone, there seems to be ample "experts" on all of the topics that come up on Rennlist.
And this should be no exception, right?
I'm sure that there are many people, here, that have measured hundreds of engines (like I have), and can guide you through the process!

I'm signing out and taking a long break from the abuse.
And searching my soul to find out what I gain from it....

For all the people that have appreciated and used my help and suggestions....you know who to thank for the above!

a4sfed928

As one who was running a motorcycle cylinder boring machine and trained in geometric dimensioning and tolerancing many years ago I will try to add some useful information.
First the title cylindricity may be misleading what you are measuring is circularity in three planes.
I think this was understood since it was struck out in the first post. There are some old methods mentioned here that have some built in accuracy that may not be obvious. Using a micrometer to set your bore gauge takes out stacked errors from different measuring devices because you use the micrometer as a transfer standard and in effect measuring the bore with whatever error the micrometer had.
Another good tip was using a feeler gauge and piston for a clearance check. I used to have 12” long very narrow feeler gauges so I could push the piston along the entire cylinder bore which by feel could pick up imperfections that a three plane circularity measurements would miss. I know some will comment on how bad a process this is but it does work.
What I learned was the boring process is quite predictable, parts heating up, bits dulling and environmental changes but the honing process was where things can get out of whack and had a certain art to it.

a4sfed928

I should have stated that using the micrometer to set the bore gauge after measuring the piston with the same micrometer was to decrease the error in finding piston to cylinder clearance, not to decrease error in determining absolute bore diameter