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Old 01-11-2017, 07:36 AM   #11
NORTON
 
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Default Re: Update on 315 exploding engines.

Hi Eric, This is a good opportunity to measure the crankshaft , using a micrometer check the bigend and main journals for size ,ovality and taper
Don't be tempted to use "plastigauge" as it won't give a correct reading for ovality.
Murray
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Old 01-13-2017, 11:53 AM   #12
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Default Re: Update on 315 exploding engines.

Hi Murray
Excuse my ignorance , but can you measure the mains with the crank in situ on those engines or is it stripped on the bench , Eric hasn't clarified where he,s at .
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Old 01-13-2017, 09:31 PM   #13
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Default Re: Update on 315 exploding engines.

Hi Drayton
Unfortunately the crank has to be removed to measure the mains
I've been down the path of increasing the oil viscosity but it is only a temporary "fix" and inevitably the machining of the crank and correct oversize bearings to regain the correct clearance to maintain oil pressure
There is obviously a major fault with this engine model most probably caused by MB trying to get more HP from a basic design
Or incorrect specs of the component
Murray
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Old 01-14-2017, 03:48 AM   #14
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Default Re: Update on 315 exploding engines.

Hi Draton and Norton
I thought Eric's idea was to do some simpler things first to see what difference they make. Whether just pulling the sump off and changing the pump or fitting a bigger pump will make a significant difference. Or on top of that new bearings ? Sounds like a really good idea to me. I do not have this motor so no worries to me anyway

We all know that a strip down, measure everything and recondition as necessary will work. But I understood this exercise is to see whether that can be put off by a much much lesser expensive intervention. All power to Eric and his friends for suggesting it and offering to do the work
Jaahn

Last edited by jaahn; 01-14-2017 at 03:52 AM.
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Old 01-14-2017, 10:50 AM   #15
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Default Re: Update on 315 exploding engines.

Thanks for the wisdom.
Just to review the issue. There are hundreds of 315's running around out there waiting to go bang. I was able to strip down the one owned by Steve315, it had done over 200k and was running normally. I contacted MB and asked what could be done to preserve the engine, I was told to replace the mains and that would fix it,but the crank and the shells looked perfect, I replaced them anyway but the engine still blew up a few months latter. That led to the development of the oil pressure monitor because it had to be a pressure problem as the bearings were ok. I thought that the oil pressure monitor would be snapped up by 315 owners but only a few got fitted. The most interesting readings are coming from Owner's 316, it loses pressure after a long hard run. This shows that even 316 owners with a few k's on should monitor there pressure. Back to the present problem, the 315 with over 250k on it has normal oil pressure until it gets hot then it falls like a rock to zero.This I think is what is happening to destroy the engines. My intention is to try to find a fix that can be applied to all 315.s out there. A bit ambitious maybe but worth a try as replacement engines are very hard to find. Eric.
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Old 01-15-2017, 11:04 AM   #16
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Default Re: Update on 315 exploding engines.

If you want to try changing the oil pump first i still have a new one which i bought last year from the UK.
steve
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Old 01-21-2017, 10:18 AM   #17
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Default Re: Update on 315 exploding engines.

I am yet to start any tests because I have a lot of other work to do first. The possibility of the engine running too hot was raised by Sprocket, recent posts mentioning very high temperatures suggest this could be common. Because the 315's do not have a temp gauge we do not know what is normal. So I think it may be best to get some base line data about water temp and oil temp and then compare that to oil pressure. MB probably want the temps high to reduce DPF problems but at what cost to the rest of the engine. Eric.
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Old 01-21-2017, 04:25 PM   #18
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Default Re: Update on 315 exploding engines.

Even though my oil pressure tap is right after the pump and upstream of the filter, >150k miles of watching engine coolant temperature, rpms, MAP or LOD (all on Scangauge) and oil pressure has told me that oil temperature is a major driver of oil pressure. Right after startup, oil pressure with Mobil 1 0w40 will easily reach the relief pressure (85-90 psig) at rather low rpms (~1500). Most of my "data" comes from watching at cruising speeds (~2500 rpms). On cool days and on the flat, with engine coolant temp in the 170F range, oil pressure is ~65 psig. As ambient temp climbs, so does coolant temp and oil pressure falls off. On the flat again, coolant temp of 185F means oil pressure of ~60 psig and coolant temp of 190F results in oil pressure of ~55 psig. I am usually proactive and slow down to keep coolant temp at or below 190F, but sometimes on long climbs it does go to the 200F range and oil pressure will fall off to ~50 psig. Interesting to me is that, on long climbs, oil pressure will start to fall even before I see a rise in coolant temp. Maybe the oil cooler should be more effective?
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Old 01-21-2017, 10:11 PM   #19
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Default Re: Update on 315 exploding engines.

Oil pressure is an indirect way of measuring oil volume delivery to the mainshaft hydrodynamic bearings.

The oil pressure itself does not keep the crank suspended, instead it is the film strength of the oil. Hydrodynamic bearings need a certain volume of oil which is roughly linear with RPM.

Oil volume can be measured if you know the oils viscosity and the pressure at a common point in the system. As the oils viscosity drops (as temperature increases) the pressure will drop for the same volume.

So a hot oil pressure of 1 bar can be completely acceptable, and a cold oil pressure of 3 bar may be insufficient.

Obviously its a bit more complicated than this, because as oil viscosity increases, the volume lost from the main bearings (and other parts of the engine) increases.

The real question is what the low oil pressure is telling us?

Is it indicating bearing wear (clearance increase)?

Is it showing reduced oil pump output?

Is it showing excessive oil temperature?

Is it showing an oil system problem (blow out piston squirter/nozzle etc)?
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Old 01-21-2017, 10:43 PM   #20
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Default Re: Update on 315 exploding engines.

I'm thinking that maybe the oil is being called upon to do too much cooling (back side of the pistons), especially since the specific power (HP/volume) of the 315 is even greater than my OM612, and, under some circumstance, gets too hot, resulting in bearing damage and then enters a vicious cycle (more and more damage at lower and lower oil temperatures) leading to eventual failure.
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