OM617 fresh from the machine shop problems!! - Page 6 - PeachParts Mercedes-Benz Forum

dkveuro · #76 03-10-2016, 11:13 PM

Quote:

Originally Posted by leathermang

Honing angle ( cross hatch ) is supposed to be 25 degrees.
" Bore cylinders in two passes. An allowance of 0.03 mm for honing is to be left in the bores. ".......................

I use the compound figure of the cross hatching.
I say tomarto, you say tomato.

.

leathermang · #77 03-11-2016, 12:02 AM

I am typing directly from the MB FSM.

dkveuro · #78 03-11-2016, 12:19 AM

Quote:

Originally Posted by leathermang

I am typing directly from the MB FSM.

I'm quoting from Google !

Engine Hone, Flex Hones, Cylinder Hones

Technical information on using engine hones, flex-hones, ball hones

https://books.google.com/books?id=AfTLFdCZ93IC&pg=PA89&lpg=PA89&dq=45+degree+crosshatch&source=bl&ots=LEMx_wZ7hI&sig=XNLLYhcPrxRqbbHPnZ-ZF92cUe8&hl=en&sa=X&ved=0ahUKEwjAp7SI9LfLAhXGQiYKHYmrDcA4ChDoAQgbMAA#v=onepage&q=45%20degree%20crosshatch&f=false

..........blah blah blah.......

Is this what you are referencing ? "..........Crosshatch............
Most OEMs and ring manufacturers say the angle of the scratches in the crosshatch pattern should be about 45° to each other, or about 22° to 32° to the horizontal deck surface. The crosshatch angle should be the same throughout the length of the cylinder and not flatten out at either end..........."

.

leathermang · #79 03-11-2016, 12:33 AM

Certainly Google is a better reference than the people who made the engines..

" Honing angle ( cross hatch ) is supposed to be 25 degrees.
" Bore cylinders in two passes. An allowance of 0.03 mm for honing is to be left in the bores. " MB Factory Shop Manual.

dkveuro · #80 03-11-2016, 12:36 AM

Quote:

Originally Posted by leathermang

.........................." Honing angle ( cross hatch ) is supposed to be 25 degrees.
" Bore cylinders in two passes. An allowance of 0.03 mm for honing is to be left in the bores. " MB Factory Shop Manual.

I fully understand, but the angle is derived from the two honing passes.....up and down incidents, total = 45 degrees.

Are you sure FSM is not referring to an angle to the head/deck surface?

.

leathermang · #81 03-11-2016, 01:04 AM

I have always used 45 degrees when doing my gas stuff including small engines.. I am just quoting what the FSM says ...I do not see any pictures saying which way they are computing it....
I do not think anyone should be doing resleeving and all this stuff without a FSM.. as there are many warnings about things which are never mentioned on any forum.

Garage Yourself · #82 03-11-2016, 11:40 AM

Quote:

Originally Posted by dkveuro

FYI...IIRC .My diesel 300d 5 cylinder engine bores were honed 2"thou from it's bored size to fit each piston as follows...

#1 piston clearance = 7/10"ths thou.
#2 thro #5 piston clearance = 1"thou.

All piston rings were OE and second rings sent to Total Seal. End gaps as per FSM .

Back in the UK a company called Hepolite ran a piston rotation test. They found the rings would rotate around the ring groove up to 7 rpm depending on engine rpm.

Total Seal second ring modification is well worth doing. I have 1% to 2% leak down on assembly and around 530 psi compression pressures after break in.

I use T/S rings on all engines as of 15 ish years ago in a Ra bore finish of Ra 12 after plateau finishing..Ed at T/S says I should use Ra20 to 25....but hey, what does he know

Honing is critical to oil consumption and ring rotation. Anything more than 45 degree cross hatch increases the ring rotation speed and ring groove wear.

Ra finish = 20 to 25 range, which is about right for most Mo coated rings and OE are down to 0.15 to 0.3 Ra finishes....which is nearly mirror finish....and talking of mirror finish........ I have been re ringing good bores in diesel engines with out first honing or roughing up the bores. Have several VW and Audi motors done this way with zero problems. Have yet to do a Mercedes diesel this way...yet.

Finally.....the bores shown here indicate the piston clearance was too tight or the coolant temp went too high. I would have liked to have seen the piston skirts. I do think the bores also tell a tale of some dirt in the assembly or inadequately cleaned bores after machining...just my 2 cents..

I tend to be super fussy about bore cleaning using MEK on a Kleenex and it must come away clean.

Please explain to me the "Total seal" 2nd ring? Talking high compression and low leak downs is like talking dirty to me, lol. I will be building a 606 soon and would appreciate the benefit of your experience!
As far as your observations:
-Too tight is the presumption, true measurements will never be known. (However I do have my gauge set to the old bore and will be able to determine if they went larger or smaller on the new build).
-Engine coolant has never been overheated, however if an oil squirter malfunctioned that could cause a hot piston, but unlikely that all 5 would be clogged or be compromised in some way.
-The bore was cleaned, as it turns out the machine shop left some media behind in the pistons after their cleaning (very small amounts were found in the pan). This was the cause of the scratched bores.

It would be appreciated if only those with hands on building experience respond in this thread, as it keeps it on point. We all have access to the FSM and understand that it holds pertinent, if not critical information regarding the assembly of the rotating assembly. Thank you

leathermang · #83 03-11-2016, 12:57 PM

" Total Seal" means that there is no vertical open space where the ring starts and stops.... it is an overlap situation.

How did this thread's assumption go from the specs you gave for the bore being Oversized for even the larger type two pistons.... to talking as if the piston to bore clearance was too little ?

leathermang · #84 03-11-2016, 01:27 PM

Quote:

Originally Posted by dkveuro

......Honing is critical to oil consumption and ring rotation. Anything more than 45 degree cross hatch increases the ring rotation speed and ring groove wear......

https://en.wikipedia.org/wiki/Piston_ring
"""It is considered good practice to build a new engine with the ring gaps staggered around the circumference of the bore. This means that any escaping gas must negotiate a labyrinth before escaping past the rings. However, while the engine is running, the rings will tend to rotate around the piston and not remain in the position as fitted. Many rings will then stick in one spot at random and remain there for the life of the engine. For this reason, ring position during build cannot be considered to be important although most engine builders would feel uncomfortable assembling an engine with the gaps aligned."""

As to building an engine and not honing.... included in that wiki article is information about ' chrome rings'.... those have been used on small engines to avoid the need for honing... but we are talking about engines with a forecast life in the hundreds of hours...not the thousands like our MB diesels.

IF it is the honing angle which affects ' ring rotation'... since it is basically even with regards to the ring surface... being an equidistant ,not directional with regard to the rings , Cross hatch... what would cause the ring to rotate in one direction as compared to the other ?... or more likely not significantly rotate around the piston UNLESS the ends of the rings were not flat or at least symmetrical. For example one end flat and the other pointed.. would clearly exert gas pressures in a direction which would cause rotation....

BillGrissom · #85 03-11-2016, 04:32 PM

I doubt you could find "total seal" or "gap-less" rings for our M-B engines. Those are marketed to racers (Chevy small block, etc) and cost ~3x regular rings. One company originally made only the 2nd ring, but now offers the top ring as well.

While gap-less rings show great improvement in leak-down tests, real-world engineering tests at >500 rpm show little correlation between ring end gap and blow-by or oil usage. There is not enough time for much gas to escape thru the ring gap. Indeed, a recent recommendation to race engine builders is to go with larger ring end gaps, since less drag forces and less risk of piston seizure.

leathermang · #86 03-11-2016, 04:40 PM

It is probably no surprise that I think that if the MB FSM is followed exactly that that is sufficient for a long and happy engine life. Billions and Billions of miles I think attest to that admittedly conservative position.
No trickiness like no gap rings are needed if the rules are followed in the first place.

97 SL320 · #87 03-11-2016, 08:30 PM

Quote:

Originally Posted by BillGrissom

I doubt you could find "total seal" or "gap-less" rings for our M-B engines. Those are marketed to racers (Chevy small block, etc) and cost ~3x regular rings. One company originally made only the 2nd ring, but now offers the top ring as well.

While gap-less rings show great improvement in leak-down tests, real-world engineering tests at >500 rpm show little correlation between ring end gap and blow-by or oil usage. There is not enough time for much gas to escape thru the ring gap.

One of the issues with a gapless 2nd ring is retaining pressure between the 1st and 2nd rings. This can cause the 1st ring to lose seal since it relies on differential pressure to increase sealing.

When pressure is above the 1st ring, it gets behind the ring and forces it outwards. Dry sump engines are set up with a restrictor in the crankcase venting system so the scavenge sections pull a vacuum to increase differential pressure. Non dry sump engines use a vacuum pump to accomplish this

Gapless rings are made by taking a standard height ring, grinding a step in the bottom then using what amounts to an oil ring rail to seal the gap.

I believe that Total Seal originally only made 2nd rings because materials would not hold up in high load applications. I'd probably only use gapless rings on an engine built to very restrictive carb / intake / cam rules where any compression leakage creates power loss. On a more open engine, there is probably more to be gained in other areas to be worth chasing some static leak down.

Leakdown is only a rough gauge of engine condition and tracking historical data is more telling than just a single test result.

Quote:

Originally Posted by BillGrissom

Indeed, a recent recommendation to race engine builders is to go with larger ring end gaps, since less drag forces and less risk of piston seizure.

Increasing ring gap does not reduce ring drag nor does it affect the piston.

Increased ring gap is done to prevent the ring gaps from closing up at high temps. When the ring gap closes up to zero, radial tension goes very high causing the ring to gouge the bore.

97 SL320 · #88 03-11-2016, 08:35 PM

Quote:

Originally Posted by Frank Reiner

The observed wear pattern is consistent with this large clearance; thrust is concentrated in a small area.

Not really, the thrust pattern is consistent with normal piston contact area.

Even with large clearance, the rings will seat fine but not last as long because the ring isn't being held square to the bore as the piston rocks back and forth.

97 SL320 · #89 03-11-2016, 08:41 PM

Quote:

Originally Posted by Garage Yourself

It would be appreciated if only those with hands on building experience respond in this thread, as it keeps it on point.

I've built countless engines and never had this type of failure on a low time engine.

The problem is definitely a piston to bore clearance issue since the wear is on the thrust side and not above where the oil ring path stops.

Try posting the pics on speedtalk.com , lots of high end builders on that site and I'd expect someone to have had seen this type of wear before even it it was on a race engine.

Garage Yourself · #90 04-25-2016, 01:53 PM

Sorry for the delayed update....
The machine shop rebuilt the short block (Backed out of there promise to cover expenses), with a smaller bore and she ran great!!!

https://youtu.be/DCsxC81KPzk

There is another twist to this story that I will address in a new thread. Thank all of you for your input on this topic!!

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode