Cylinder leakdown higher after engine rebuild?

[bigjae46]

Some of the best advice I have gotten have not been from BMW know it all shops like VAC or Metric Mechanic. One was a dune buggy fabricator that had an in house engine builder. The other was a machine shop that did mostly aerospace work in Wichita, KS.

The machine shops in Houston mostly suck.

As far as your issue...I feel for you. You'll probably get better info from this forum than you'll get from most of the BMW "specialists".

[oceansize]

You'll probably get better info from this forum than you'll get from most of the BMW "specialists".

These BMW "specialists" won't even come on a forum like this. Too proud and think they have it all figured out. Much more respect for shop owners like George Hill and occasionally Kaiv who come on these forums read, participate, and post. I'm sure there are other shop owners here as well and perhaps some who at least lurk. An expert is someone who has been burnt so many times they've developed a gut instinct for when they need to pause and reach out for help.

[Chanman1029]

Some of the best advice I have gotten have not been from BMW know it all shops like VAC or Metric Mechanic. One was a dune buggy fabricator that had an in house engine builder. The other was a machine shop that did mostly aerospace work in Wichita, KS.

The machine shops in Houston mostly suck.

As far as your issue...I feel for you. You'll probably get better info from this forum than you'll get from most of the BMW "specialists".

I think I remember you mentioning that machinist in wichita, what all kind of work can they do? At some point I’d like to have my spare crank and block machined, it will need the journals re welded. Safe to say I’m searching for a new shop to send my future work to.

[sapote]

While I do agree with you, my fear is that the metal wear will only get worse, and further damage the cross hatching, which would then cause excessive oil burn.

I think I am going to drive it a little more, do oil changes more often and see how metal content in the oil improves or declines.

I don't know if the shop - Lang - had done any post machine work on the new honed cylinders or not. Depend on the honing process, the newly cut cross hatch lines have uneven height sharp peaks and they should be processed to have a plateau instead. To get the plateau, a nylon ,or other material, brush is rotating to change the peak to plateau and clean up the metal debris, then washed off. If not done, then the new rings would do the job of creating the plateaus but process also wears down the new ring edges, which is not good.
Hopefully after some more miles your rings will seal better than now.

[sapote]

A good read on the subject:
ttps://digitalmetrology.com/tutorials/plateauhoning/

https://www.aa1car.com/library/plateau_finish.htm

[Chanman1029]

A good read on the subject:
ttps://digitalmetrology.com/tutorials/plateauhoning/

https://www.aa1car.com/library/plateau_finish.htm

This hurts my head, I’m gonna have to read that like 5 times to comprehend it

[bigjae46]

I think I remember you mentioning that machinist in wichita, what all kind of work can they do? At some point I’d like to have my spare crank and block machined, it will need the journals re welded. Safe to say I’m searching for a new shop to send my future work to.

He does not machine cranks. The quote I got from a different machine shop that does cranks for airplane engines was $1200 including reweld, machine, straighten, balance and heat treat.

This shop does all of the other stuff you might need. Honing, cutting the rings, balancing the rotating assembly.

I also use a shop that does REM polishing. He will not deal with retail customers. He does all of the rem polishing for well known vendors. Let’s say the service is HEAVILY marked up.

I charge less than half for the same thing in most cases unless it’s a crank or camshaft.

[digger]

What are the details of the build? What size bore/pistons, which bearings were used (main and rod), what fasteners, etc? Cylinder spacing, ring gaps, block and head deck amounts, material of pistons, etc

call out where anything is not stock.

ok, I just reread where you talked about not knowing the bore size. Here’s the issue, as the assembler you need to know all the intimate engjne details and be able to double check work before you assemble.

this is not fun to hear as you received the short block assembled, but by receiving it assembled you left someone else in charge of a QA/QC step you could no longer do.

this is prolly where the hard lesson is.

lang should have all of your specs written down. If they don’t, that’s their responsibility.

you should also have them and be able to verify

now, o know you paid money to remove that risk, but the compounding issue that there’s no way I’d warranty a part of a build if someone else had control over something I did not. This is the situation Lang is in.

it sucks for both of you. Shared assembly responsibility. It will always be a he said, she said

There is nothing wrong with letting an expert do the QA/QC as they will know more than anyone on this forum. The trick is to know who is an actual expert and who is a salesman. I would say all the big name BMW places are sales people or basic mechanics with enough knowledge about engine assembly to be dangerous.

From Lang perspective there are things the customer could do that would cause issues not related the quality of machining , or workmanship during assembly so i get the no warranty. However if they had credibility they would want to assist in determining the root cause. and rectify if they are to a contributor to the issue

[digger]

I don't know if the shop - Lang - had done any post machine work on the new honed cylinders or not. Depend on the honing process, the newly cut cross hatch lines have uneven height sharp peaks and they should be processed to have a plateau instead. To get the plateau, a nylon ,or other material, brush is rotating to change the peak to plateau and clean up the metal debris, then washed off. If not done, then the new rings would do the job of creating the plateaus but process also wears down the new ring edges, which is not good.
Hopefully after some more miles your rings will seal better than now.

best practice seems to be to use very coarse diamond size to within a tenth or so then plateau with 600grit for a dozen or so strokes. depends a bit on block harness and material

the old practices of using several stone and finish honing to size the last thou or so with a fine stone is outdated. the plateau is done by 600grit that doesn't change the size by more than a tenth or two to avoid remove the valley that hold oil and lubricate the newer ring materials

[R717]

That's pretty frustrating how Lang is treating you. It's critical to get the required cylinder wall specs from your piston and ring manufacturer, and be certain the cylinders are honed to those specs. This has tripped up several fellow air cooled Porsche owners when getting nikasil cylinders replated. After tear down it would be interesting if you could get profilometer readings on areas of the bore that didn't get swept by the piston to see what Lang delivered you. Here's an article to get you started on your research:

https://www.enginebuildermag.com/2020/11/hone-in-on-honing/

[tlow98]

There is nothing wrong with letting an expert do the QA/QC as they will know more than anyone on this forum. The trick is to know who is an actual expert and who is a salesman. I would say all the big name BMW places are sales people or basic mechanics with enough knowledge about engine assembly to be dangerous.

From Lang perspective there are things the customer could do that would cause issues not related the quality of machining , or workmanship during assembly so i get the no warranty. However if they had credibility they would want to assist in determining the root cause. and rectify if they are to a contributor to the issue

completely agree and well put.

[STAATS]

Interesting that he wouldn't give you a build sheet... I am based on Australia and had him build me an engine and send it to me... would have been ~2018 I think. He was good, although I can see how some of the issues you have with him would happen, he was nice and supportive and answered a lot of stupid (on my part) questions but I could see examples of him getting defensive about stuff. Nothing major so it never impacted me but I can definitely see in a different situation how it could be problematic. Anyway when I got mine done I remember getting a warranty of sorts, it was like 10000km/3M or something like that, I remember him messing around with it for a bit as he wanted to make sure he wouldn't have to deal with any support issues with me as I was on the other side of the world (which was obviously fine by me), he also told me to use stock oil for break in back then, I used a conventional break-in oil anyway but yer funny that he has changed when normally that's part of an engine builders secret sauce so to speak... I also managed to get a build sheet off him for the setup he did for mine. When he did mine I originally paid for Mahle pistons but he went through 2 sets and he wasn't happy with the manufacturing tolerances and actually upgraded me to CP pistons without charging me any extra. So definitely sounds like maybe additional business has reduced their quality or customer focus, sad to hear...

[Chanman1029]

Interesting that he wouldn't give you a build sheet... I am based on Australia and had him build me an engine and send it to me... would have been ~2018 I think. He was good, although I can see how some of the issues you have with him would happen, he was nice and supportive and answered a lot of stupid (on my part) questions but I could see examples of him getting defensive about stuff. Nothing major so it never impacted me but I can definitely see in a different situation how it could be problematic. Anyway when I got mine done I remember getting a warranty of sorts, it was like 10000km/3M or something like that, I remember him messing around with it for a bit as he wanted to make sure he wouldn't have to deal with any support issues with me as I was on the other side of the world (which was obviously fine by me), he also told me to use stock oil for break in back then, I used a conventional break-in oil anyway but yer funny that he has changed when normally that's part of an engine builders secret sauce so to speak... I also managed to get a build sheet off him for the setup he did for mine. When he did mine I originally paid for Mahle pistons but he went through 2 sets and he wasn't happy with the manufacturing tolerances and actually upgraded me to CP pistons without charging me any extra. So definitely sounds like maybe additional business has reduced their quality or customer focus, sad to hear...

yeah I dont think there was ever a time when I felt like he was being nice or supportive. He too answered alot of my dumb questions, and made recommendations, but that was about it. He just seemed agitated the whole time I was talking to him when dropping off my motor, never smiled one single time, just a RBF. I asked him if he could also send in my valve cover and oil pan to get cleaned with my block and head, and his response was, “it’ll cost extra”. I wasnt too bothered, and I said yeah thats fine. I wasn’t expecting it to be free so we moved on.

once I was about to pay, I asked if I could get a shirt and a coffee mug that were on display behind the counter, and he said “they’re not free”. Like dude, I’m not asking for you to give me free stuff, stop being a damn jerk. That one really grinded my gears a bit, but I just let it go.

I’ll never recommend Lang to anyone

[Anri]

bc he doesn’t warranty any work that involves non oem parts. Its all over his website.

Have you thought about why..?

Regards,
Anri

[Chanman1029]

Have you thought about why..?

Regards,
Anri

I think a time or two…