Mi16's Die And S16's Don't...

[wicked 103 3 Cars]

The oil surge on the Mi16/S16 has been discussed here on the forum many times and the status quo is (I think) that it caused by the MI16/S16 head retaining the oil, due to the shape of the head and small drains towards the sump. The issue has been addressed by Peugeot with new design of the RFS and XU7J4 heads. On the EW engines, the drains are even bigger and put on the back side of the engine (Look at Sandy's topic about the EW's). On 8v engines this not an issue.

For the Mi16/S16's there are a number of fixes to avoid oil surge (larger sumps, sump baffles, windage tray,..), but I newer understood why a Mi16 dies on oil surge, popping the famous second rod, and a S16 survives oil surge more easily.

It has been said that it was caused by the piston located rods, but an experiment on a Mi16 with 1.9 8v rods also ended in a dead engine as well.(search on the forum for that)

 

So there must be another difference between Mi16's and S16's and I think I found it.

The difference is in the oil supply, through the crank towards the rod bearings.This is determined by the design of the crank. I had both cranks lying on my desk and suddenly noticed that the S16 crank had more holes in the main bearings.

Find below 2 pictures (not my cranks) were I added the oil flow through the crank.

 

Mi16 crank:

 

 

All main bearing get there oil from the main tube on the front side of the engine. The main oil tube is supplied by the oil pump, close the the second main bearing. From main bearing no 2 and 4, there are oil ways inside the crank towards the rod bearings. So 1 main bearing is supplying 2 rod bearings!! This is also the case with XU9J2 cranks. Note that the oil supply of a main bearing is restricted by a small hole in the bearing it self.

 

If you compare that with the S16/2.0 8v Turbo crank:

 

 

You'll see that in 4 main bearings an oil way towards a rod bearing is present. So every rod has a dedicated supply from a main bearing and there is no oil sharing between rods inside the crank.

 

 

 

Consider the case that you turn in on a left corner and you get oil surge.

The oil supply to the main oil tube will stop and be drained towards the oil pump, via the supply (and leakage on the bearings)

Looking at picture below, you'll see how the oil flow changes (yellow arrows) on a left hand corner surge.

 

 

The supply of the main oil tube is located closest to the oil line towards the 2 second main bearing feed. This bearing is feeding the 1st and 2nd rod. So this one will surge first. Due to the cornering force (big yellow arrow), the oil that is left inside the crank and mean bearing feed will be forced towards the 1st rod. So (famous) second rod dies first.

But how about the 3th and 4th rod? In the main oil tube there is a little more pressured oil left that will supply the 4th main bearing a little longer.

 

Note the feeds towards the main bearings are not balanced in terms of flow:

 

Main bearing feed 1: main bearing leakage

Main bearing feed 2: main bearing leakage + 2 rod bearings leakage

Main bearing feed 3: main bearing leakage

Main bearing feed 4: main bearing leakage + 2 rod bearings leakage

Main bearing feed 5: main bearing leakage

 

Keep in mind that the supply is restricted by the small hole in the main bearing.

 

Compare that with the S16 crank:

 

 

More balanced flow and no oil sharing in the crank:

 

Main bearing feed 1: main bearing leakage + 1 rod bearings leakage

Main bearing feed 2: main bearing leakage + 1 rod bearings leakage

Main bearing feed 3: main bearing leakage + 1 rod bearings leakage

Main bearing feed 4: main bearing leakage + 1 rod bearings leakage

Main bearing feed 5: main bearing leakage

 

So feed 2 and 4 of the Mi16 comsume more oil and are the first ones to get empty if you have surge. The S16 feeds will be kept filled longer and more equally. Once the oil pressure recovers, the oil lines inside the cranks have to be filled again. The volume of an oil line inside a Mi16 crank is larger (towards 2 rod bearings) and has to be supplied by 1 feed, through 1 main bearing. So it will take more time in a Mi16 crank before oil pressure on the rods are restored.

The 2nd rod of a Mi16 will lose pressure earlier and recovers later, compared with a S16 and will wear out faster.

 

So comparing the defects on the PSA engines:

 

XU9J2 XU9J4 XU10J2 S16 RFS XU7J4

no sump baffle x x x/- -/x - -

oil retaining head - x - x - -

floating pin - x - - - x

low flow crank x x - - - ?

 

The Mi16 is the only one to have a oil retaining head AND low oil flow/oil sharing through the crank.

Floating pin is also found in XU7J4 and not an issue.

 

These were my findings of last weekend.

Feel free to shoot at it, we'll all learn from it....

 

Just my 2cents...

[TT205 42]

Well done that man!

 

This sounds very feasible

[welshpug 1,622]

so who's going to do the testing to see if this theory holds oil

 

 

ps, my iron block span No4 big end on a left hand bend, which seems to be further from the oil pump than No3 in oil routing, though the same as No2

 

I think you have numbered your bearings incorrectly, No1 is at flywheel end!

 

Also this is not purely surge, but starvation, oil surge in itself is not a problem if it does not cause oil starvation !

[wicked 103 3 Cars]

I started numbering from timing belt, so indeed numbering should be swapped.

So indeed, your No4 is my No2.

 

Starvation might me the term to use. (I'm not from UK ;-) )

In the end this will not fix the drop in oil pressure; it only explains why Mi16 die faster than S16's.

 

Bearing/rod ID:

 

Edited May 23, 2012 by wicked

[kyepan 291]

this is smart thinking, i'm going to digest this!

[welshpug 1,622]

indeed, time to dig out an 8 valve XU5/9 crank and see what that is like, all XU10 cranks bar the T16 is the same.

 

Also might be worthwhile checking the XUD9 and DW10 cranks being 88mm and forged steel...

[wicked 103 3 Cars]

XU9 cranks have similar oil ways as the Mi16 one.

Edited May 23, 2012 by wicked

[DrSarty 90 1 Cars]

XUD9 and DW10 cranks being 88mm and forged steel...

 

Perhaps a silly, obvious question, but does the above mean an Mi16 XU9J4 can be fitted with an XUD9 or DW10 crank to help fix the issue?

[welshpug 1,622]

if they route the oil differently, then yes

 

same as you have used an XUD11 crank in the past.

[Alan_M 66 1 Cars]

Perhaps a silly, obvious question, but does the above mean an Mi16 XU9J4 can be fitted with an XUD9 or DW10 crank to help fix the issue?

 

But you'll still have the head issue. Surely, swapping cranks will only give you a bit more time before that light comes on.

 

From what I've read, either reduce oil going to head by solid lifters & restricter, and/or return more oil quicker by fitting the external drain line.

 

Excellent thread by the way wicked.

Edited May 23, 2012 by Alan_M

[TT205 42]

But you'll still have the head issue.

 

But is it an issue?

 

Just playing devils advocate we know the head is slow to drain and we have presumed this is the biggest issue - but is it?

 

Over the years on these threads we have had Mi's with all the sump mods still spinning a shell and even standard Mi's that have for no apparent reason remained bullet proof

 

At the end of the day if you are getting oil starvation at specific shells then Wicked's finding seems very logical. You can all of the surge in the world and way too much oil in the head but if it doesn't actually result in starvation then there is no damage and it becomes irrelevant

 

I'd love to know if this is the holy grail!!

[wicked 103 3 Cars]

The head is an issue; just have a look at the oil return in a Mi16 head at the distributor side. The oil almost needs a map to get out of the head...

And Peugeot did change it...

 

I also did some searching:

Some DW10 cranks have Mi16 style oil way, some have S16 style oil ways. It seems that the later 110bhp version is similar to the S16.

 

I also found a picture a XU7J4 crank and that one has also the S16 style oil ways.

This block is a wet liner, with RFS style head and a reputation of being indestructible.

Edited May 23, 2012 by wicked

[DrSarty 90 1 Cars]

I'd read people arguing that the head wasn't the issue, although Wicked has shown some evidence that at the very least it's a contributing factor.

 

The crank observations seem far more logical as the major cause, and the head 'issue' can be much reduced by having more oil in the engine, which is achievable by putting more in if safe to do so, especially if you've a modified sump that increases capacity. Not many of us have mind.

 

It could also be reduced by adding an external head drain to the sump. Has anyone done this and got pics?

 

It would appear then - if this is all correct - that an XU9J4 (alloy block) Mi16 could be made less prone to oil starvation which causes a spun shell by the following:

 

...fitting a dry sump system or...

• fitting a better crank, dimensionally the same - i.e. later DW10 or XU7J4
  
• (possibly fitting the 8v rods?)
  
• increasing oil capacity (more in as standard or via a modified sump)
  
• adding an external head drain to the sump
  
• fitting a (PeterT-type) extended oil pump pick up
  
• fitting an oil pump chain guard
  
• fitting a 6bar S16 pump spring
  
• fitting the pump baffle
  
• fitting a windage tray (difficult on an XU9J4 due to block stiffener mods required, and new windage tray fittings needed or use of 4 x S16 main bearing bolts on cyl 2 and 3 which have the windage tray fittings)
  
• using a baffled/trap door sump (e.g. GTI6, S16 or custom)
  

Can the battle be won?

Edited May 23, 2012 by DrSarty

[Batfink 201]

I know a guy who still spun his shells with a full dry sump system on his mi16 race engine so its not the be all end all to lack of oil lubrication...

I think we all know where the issue lies (the head) and then poor engine tolerances due to age, its just whether people want to spend the money to fix it or go the cheaper option of attempting to alleviate the issue with extended sumps and so on.

Edited May 23, 2012 by Batfink

[unariciflocos 49 1 Cars]

My Mi16 spun no 1 rod and I'm sorry but I don't agree that this is the problem. An engine needs oil PRESSURE, not oil presence. Once the oil pump is in the air it doesn't matter what oil is left in the crank. The moment the pressure drops the damage begins. The only cure is making sure the oil pump is never starved and the cheapest option is increasing oil capacity.

 

I'll be adding a pressurized accumulator with an extra 2 liters of oil as soon as I get home and I'm sure this will help significantly.

Edited May 23, 2012 by unariciflocos

[Batfink 201]

why are people so resistant to sorting getting oil from the head back to the sump or stopping the demand by using solid lifters and a flow reducer in the oilway? We can throw oil at the problem all day long but its heavy and simply masks the flaw rather than cures it

[DamirGTI 325]

Extra oil capacity will be as bad as low if you plan on using same , std. sump volume .. the crankshaft will "wind" the oil mixing it with air which will create air bubbles in the oil and oil foaming and this'll be even worse for the bearings , they'll go bust in no time .

 

Damir

[unariciflocos 49 1 Cars]

How do you know you're not sacrificing head lubrication by adding a drain? Maybe you cure the bearings and lose the cams. What size restriction would you use?

 

Peter Taylor has a 1.5 liter accumulator on his car which provides 10 seconds of oil pressure after the pump is in the air, no corner is longer than 10 seconds.

 

Damir, oil level in the sump will stay the same, the extra 2 liters will be in the accumulator.

[wicked 103 3 Cars]

@ batfink: I never denied that the real cause is in the head or posed that it could be fixed with changing cranks.

Mi16's and S16's share the same head, but Mi16's die more often due to that problem and in most cases (not all) it's the shell that I marked as rod2.

So I only tried to clarify a flaw of the Mi16, not masking it...

 

Adding a proper drain to the head is not that easy!! It's hard to find a place where you can drill a big hole that will drain the head enough.

It's done before and not always a succes....

[allanallen 528 2 Cars]

I always think you never hear about s16s surging to death because bugger all people are using them compared to the 1.9 mi??!!

 

It's interesting stuff about the cranks but I can't help thinking it'll make very little difference in reality. If there's no oil at the pick up the crank will run dry regardless of how the bearings are fed.

 

The main concern in my opinion is why do some engines surge and die on the road and others take years of abuse on track with slicks?!

[Miles 331 1 Cars]

Yes S16's and GTi6 surge, seen it more than once

[unariciflocos 49 1 Cars]

Never try to drill anything ON the engine, getting metal debris in the oil will surely lead to damage.

 

Looking at the statistics as others have said, hearing of less S16 that fail is only due to the fact that they are used less.

 

The only cure for this is making sure the pump pick-up is submerged in oil at ALL times. This should be the only track for all of us doing the R&D and trying to find a solution.

[Mad Scientist 106]

I know a guy who still spun his shells with a full dry sump system on his mi16 race engine so its not the be all end all to lack of oil lubrication...

I think we all know where the issue lies (the head) and then poor engine tolerances due to age, its just whether people want to spend the money to fix it or go the cheaper option of attempting to alleviate the issue with extended sumps and so on.

 

In reference to this, the system must have been installed/designed badly. A drysump system can only lose pressure if the oil in the tank surges, the belt comes off the pump, or there's not enough oil in the system.

 

Interesting ideas from the OP. Will keep an eye on this.

[Cameron 16]

Nobody seems to have mentioned fitting a GTi6 head to the Mi16.

 

I ran my engine for over 3 years on semi-slicks and never had a whiff of oil starvation.

 

I think you may well have figured out the issue here, but to be honest I don't think swapping cranks will help much, just as I didn't think crank-located rods would (and look what happened there, quietly, a year or so after I was shouted down!) I digress.. So the point is that on an Mi, 2 big end bearings are supplied from 1 main; so once the oil supply pressure is reduced by surge / starvation / whatever you want to call it, the pressurised oil in that main bearing is being consumed twice as fast as with the S16 design, which may be the millisecond difference between damage or not.

 

In my opinion though, what happens in the bearings once you remove the oil supply pressure is irrelevant, and you'd be chasing hundredths of a second in trying to solve this. What's FAR more important is to ensure that the supply pressure doesn't disappear in the first place! The standard combination of baffled sump and windage tray goes some way towards this - further than swapping cranks would, certainly. Fitting a deeper sump, extended pickup and more oil is very low on my list of sensible fixes for reasons that should really be obvious. Reducing the oil capacity in the head and improving drainage is one of the best things you can do - just look at how all modern production engines are designed! A GTi6 head does this, and in my experience does it very well.

Edited May 24, 2012 by Cameron

[allanallen 528 2 Cars]

Nobody seems to have mentioned fitting a GTi6 head to the Mi16.

 

I ran my engine for over 3 years on semi-slicks and never had a whiff of oil starvation.

 

 

I'm sure I've asked this before but was your mi a known 'surger' before you fitted the 6 head?