Update on 315 exploding engines.

Thanks for the info Timbo,

Is the baffle attached to the pan or block ? Can it be got at easily? What's involved in fitting new pickup pipe for oil pump? Is it accessible from below as well ?

cheers
Col

Hi Col
The baffle plate is attached to the main caps and access can be gained by removing the sump which can be done with the engine still on the car. The pick up pipe comes right off the back of the oil pump in the same area. It's only held in by a male torx bolt with an o ring. As for the difference between the old oil pick up and the new one, I'm not sure. Maybe someone has an early model 315 engine sitting around and may have a picture to compare.

New member. Just come across post about main brgs. Seems to me that the added power of this engine compared to lower HP units is the main caps not robust enough and leads to main cap stretching and losing the crush size of the block/cap. This measurement is critical to retaining brg in block and giving correct brg clearances. As the caps distort the crush is lost allowing brg to spin in main tunnels and also closing off oil feed gallery, having smaller cap bolts does not help. The engine should be stripped and tunnels miked for size and ovality. If okay new bearings fitted and tentioned, then checked for crush by releasing one cap bolt and measure with feeler gauge under mounting face. It should be in the range of .006". anything less could lead to brg spinning in tunnel. To rectify it requires machine shop to remove material from cap mounting face and linebore back to standard tunnel bore with the fitment of larger diameter bolts. The tabs on brg shells are purely to locate brg in tunnel and play no part in stopping it from from spinning in block. This all boils down to design fault by not fitting heavy duty caps to take the added power. Regards Jack.

Thanks for the info Jack. I haven't moved much further forward with my rebuild yet but I have measured all of the caps for taper and ovality and all are within spec. I have looked over the bottom end to see if it can be strengthened in any way but there isn't much to work with. Maybe just turning down the boost may be easier.

In the olden days it was common to find over size main tunnels. they could be all of them or just 1 with factory brg shells of + .015" unavailable from dealers. It was also common to find 1 crankpin or main journal .010" undersize. So every engine needed to be measured completely. Factories producing millions of engines have a system of selective assembly to make up differences in tolerances to ensure proper clearances. For this reason it is important to check the crush with brgs insitu. Checking tunnels for taper and ovality is not going to tell you crush is ok. We used to fit steel main caps to racing grey engines which cured cap problems, so they began producing more power only to rip the webs out of the block. You hit the nail on the head by backing off the boost, exceeding the elastic limit does not work. Regards Jack.

Just a note on checking bearing clearances without micrometers . This is done in all machine shops, can also be done with engine insitu. First check crush by tentioning bolts and then releasing one of the bolts, then check how far cap moves up with feeler gauge, .006" would be the minimum. If okay then remove cap and place piece of gloss magazine paper on cap and retension. If crank locks up or becomes firm to turn you know the clearance is less than the paper thickness. Gloss paper is normally .004". If crank still turns easy insert piece of news print on top of gloss and crank should lock solid. News print is usually .0025". The nominal clearance for copper lead brgs is .002" to .004". this is an extremely accurate method of checking crush and clearance. This can also be used on rodshells. The more i read these posts the more i think the under done cap bolts are a big part of the reason for falling oil pressure by growing and releasing some tension, This can also lead to less crush and allow brgs to spin. Is there an aftermarket oil cooler available.?

Thanks for the info. I am currently waiting on main bearings from the UK to arrive to move forward. I think i have mentioned on this thread previously about the main cap bolts being M11 and relatively short compared with other engines (om651 has M12 cap bolts around 40mm longer). Another thing I have noticed is that the bolts are threaded along the whole length meaning there is no shank section. With the bolt almost all of the way in the cap is able to move forward and back due to the thread of the bolt being smaller than the hole through the cap. This makes the head of the bolt take the clamping load on the cap as well as having to keep the cap centred over the journal. I'm not saying it moves much but it may be enough over time to contribute to a failure. If the shank of the bolt fitted snuggly against the main cap bolt hole and then is torqued down it may prevent this movement from taking place.

Timbo
The screws are threaded over the full lenght for a good reason, When the screws are tightened to the elastic part of the stretch it is distributed over the lenght of the thread so does not get to the elastic limit on a few threads. The caps are located by the tight fit in the block. If the caps are not still tight in the block the caps and block are not reusable. Eric.

I understand that the bolt is torque to yield and the caps do fit tightly into the block however I am discussing possible strengthening of the current set up. If I just want to put what Mercedes has done already back into the engine then I can't really expect a different result. I'm not saying that it would be a definitive answer but Im just looking at different points I can identify as possible weaknesses while I have the engine apart. I have looked at the possibility of a girdle, larger main cap bolts (not possible as there isn't enough room) Now I am comparing the main caps and bolts to other engines I have worked on. I was just concerned by how much movement there is between the cap and bolt. If just 5mm of this bolt was unthreaded and closer to the size of the cap bolt hole I think it would add stability against thrust forces. That would leave just over 70mm of threads to stretch......... But I'm no engineer

Below is a picture of a big end cap bolt. What I am referring to is the section just under the head before the threads start.

Timbo.
I understand what you are thinking but the problem is the cap flexing or bending under load, changing the design of the screw would not make the cap stronger. Eric.

Your right, it won't make the cap stronger but is the cap flexing by 'borrowing' wiggle room from the way the caps are attached to the engine. ARP may disagree that the screw makes no difference in strengthening the main cap assembly. These again are just ideas though. I do take your critical thinking on board Eric. The difference for me is that my engine only had a broken piston and the crank assembly is OK but I would like it to last without having to think about it every second I am driving.

Timbo,
Sorry I have forgotten which model you have but it was only the 07 model that had the problem. Eric

Hi Eric
My one is an 08 model. I think at one stage we were trying to work out if there were differences with the later model ones as far as the main caps etc. The problem was that my van was several hundred km away. I have since pulled the engine out and put it in my garage for the rebuild. Just going through it now, cleaning and preparing for it to go back together.

Hi all, I have a brand new oil sensor kit that I no longer need. Its unused and is all there. If you've been reading this topic you will know what it is and what Eric as discussed about installing it. I'm in Sydney or could of course post it anywhere. It cost me $55 so close to that if anyone wants it.

Timbo. while you have crank out test for cracks by holding it up by piece of rope and tapping all counter weights with hammer. You will get nice tone if all is well. A crack will give a dull note. You probably know that.

Thanks Jack. I have heard of this method before but never used it. Normally I just send them to the engine reconditioner to have them checked out. I have about 3 shops withing 20 minutes of my house. Prices aren't to bad either. I have been cleaning and painting the engine block this morning getting ready for the arrival of the bearings. I have new big end bolts on the way and I am currently looking for new main bolts. Anyone know who is selling them apart from the dealerships?

Chris02
I would be interested in taking that oil pressure sensor kit if you still have it

I Finished my apprenticeship in engine reconditioning in 1952 when there were still plenty of older cars on the road. heaps of solid run babbit brgs, copper asbestos head gaskets, and dodgy fixings. If head gaskets lasted 12 months it was normal. I was second to start with Carveth Sproule later to become GEM Engines. Tens of thousands of engines went through during my stay there. Head gasket technology and self locking high tensile head and main bolts were not consumeables but were used time and again. The head of the bolts were designed to distort and keep tension on the thread after torqued. I cannot understand why they fixed something that was not broken with the introduction of torque to yield bolts. They are smaller in diameter and must be cheaper for the bean counters. That is my rant for the day

Timbo30aus said:

Hi Eric
My one is an 08 model. I think at one stage we were trying to work out if there were differences with the later model ones as far as the main caps etc. The problem was that my van was several hundred km away. I have since pulled the engine out and put it in my garage for the rebuild. Just going through it now, cleaning and preparing for it to go back together.

Click to expand...

Someone was talking about putting a locating collar in the block aroubd the bolt hole and machining the cap so it locked into this collar. The theory seemed sound to me, in that the cap distorting downwards would pull inwards at the bolts. Eventually causing the bearing shell to contact and spin. The collar would prevent this from happening. It was a couple of pages ago?