MI16 1.9 Forged Piston Issue

[Andy F 0]

Hi Everyone 

 

With the 205 being buried in the back of the garage for a few years, while I’ve been building a house I’ve finally finished and am

keen to get the 205 finished.

 

Having helped some friends rebuilt some other XU’s recently I’ve realised I may have a bit of issue with my pistons and was hoping for some advice. 

 

In building my engine I used Wossner high comp pistons and PEC steel con rods. The difference on these from normal MI pistons/rods is they float at the small end. As the MI crank floats at the big end I’m now concerned the pistons might be floating at

both ends. 

 

Does anyone have experience of this piston/rod combo. I wondered if anyone had any ideas of how I could solve this if it does turn out to floating to still allow me to use the pistons and rods, maybe a different crank?

 

Many thanks for any guidance 

Edited January 7, 2018 by Andy F

[wicked 103 3 Cars]

Mi16's float on the big end because the oem mi16 rod has less width than other oem rods with same crank. Most likely the pec rods are wider than the oem rods and do not float on the big end. I would remove the sump and check to be sure...

 

[petert 586]

You are right to be concerned. Aftermarket piston manufacturers seem to completely ignore the fact that Mi16 pistons centre the rods. Technically, it's a superior solution but more difficult/expensive to achieve. If your rods are Mi16 width on the big end, you may indeed end up with cracked piston bosses. One method of overcoming this is to order rods with 8V width big ends and 22mm full floating small ends. Another method is to machine the inside of the piston parallel and make thrust washers, as I have done here with these Iapel pistons.

[Andy F 0]

Thanks for the replies. I think I’ll wip the sump off and have a look.

 

the above option to stop the piston floating seems simple enough so probably the way forward if the big ends are not wider than normal.

[wicked 103 3 Cars]

11 hours ago, petert said:

 Technically, it's a superior solution but more difficult/expensive to achieve.

 

For my curiosity; why is it better? I've also heard people saying that crank located rods are superior for (keeping) oil pressure. 

[petert 586]

I thought friction. You don't have a rod smashing against the crank webs.

[welshpug 1,657]

doesn't seem to slow down all those Yank V8's, they smash the rods against each other as well as the crank.

 

 

wasn't it the rods supposedly part of the oil consumption issues with the Mi16 as well as the large cavities in the cylinder head?

[Anthony 1,003]

2 minutes ago, welshpug said:

wasn't it the rods supposedly part of the oil consumption issues with the Mi16 as well as the large cavities in the cylinder head?

 

That theory was debunked wasn't it after Martin (CRF450) built an engine a few years back using 8v rods that, after initially looking promising, still suffered starvation?

[allanallen 528 2 Cars]

48 minutes ago, Anthony said:

 

That theory was debunked wasn't it after Martin (CRF450) built an engine a few years back using 8v rods that, after initially looking promising, still suffered starvation?

Yep, debunked! It may have helped but the engine (nicks) still died (again) through oil issues.

[Andy 105 1 Cars]

Hypothesis as follows. Stick foot on clutch and crank makes a bid for freedom at the timing belt end. Well, not quite, but the crank will move axially as much as the thrust washers allow . If the rods are crank centred, there is almost no axial movement, hence the rod too moves axially with the crank. Now, that axial translation has to be transmitted to the gudgeon pin, along which the rod can slide. However, that pin is a good 158mm away (RSengine, 153mm if 10j4) . That is a lot of bending moment which will tend to put side thrust onto the piston ( I think Peter just said this , but in about 10million fewer words) . If the game is played the other way around, and the rod is piston located, the rod is free to slide axially . This time the bending moment is transferred to the rod/ crank bearing and is instead just the crank throw (43/44mm ) which means that (a) the rod is likely to slide axially and (b) transfer no side thrust to the piston .

 Not this is a hypothesis . The Physics adds up ( well, on planet Andy it does) but it may be complete and utter oblate spheroids .

[wicked 103 3 Cars]

It think measuring if the big end of the rod is 22.5mm or 24.45mm wide is enough?

[Andy 105 1 Cars]

24.45 and it is crank guided. 22.5 ( same as small end) and it is piston guided. However, the snag will be if the piston is not 22.5 , but much more, and the big end is 22.5 as it should be. Then you have rods that are guided more by faith than machinery . I hope it all works out o.k for you . Aftermarket pistons can be tricky as I am discovering by doing some research and making phone calls. 

[Andy F 0]

According to PEC website (having not yet checked my engine) states the big end width is 22.5mm same as small end. I guess this means the rod won’t be guided at the big end.  Guess I’ll have to hope that between PEC and Wossner they have considered this

[petert 586]

Maybe if you asked nicely, PEC would make you a 1.9L 8V rod with a 22mm small end? In reality, that's what aftermarket Mi16 rods should be.

[wicked 103 3 Cars]

On 7-1-2018 at 8:24 PM, Andy F said:

 

In building my engine I used Wossner high comp pistons and PEC steel con rods. The difference on these from normal MI pistons/rods is they float at the small end. As the MI crank floats at the big end I’m now concerned the pistons might be floating at

both ends. 

 

But did it float on the piston? 

[welshpug 1,657]

14 hours ago, Andy F said:

According to PEC website (having not yet checked my engine) states the big end width is 22.5mm same as small end. I guess this means the rod won’t be guided at the big end.  Guess I’ll have to hope that between PEC and Wossner they have considered this

 

I would not discount anything, it is known that they have issues with incorrect valve cutout centres dome heights and compression volumes on a few designs.

 

13 hours ago, petert said:

Maybe if you asked nicely, PEC would make you a 1.9L 8V rod with a 22mm small end? In reality, that's what aftermarket Mi16 rods should be.

 

I doubt they make them themselves, given they look identical to a MAXPEEDINGROD, and many many other far eastern supplied rod and piston.

 

Why an 8v rod also?  with its shrink fit pin and otherwise same length, but a much wider small end?

 

 

I thought the MI16 was crank located given the pistons don't have a machined surface for the small end of the rod to bear against whereas the 8v does, and the 8v has much less side float on the pin?

 

 

[Andy F 0]

7 hours ago, wicked said:

But did it float on the piston? 

Honestly can’t remember was nearly 5 years ago I put it together. I have some photos but doesn’t really help much. I just recall something in the spec mentioning they were floating

 

[Andy F 0]

5 minutes ago, Andy F said:

Honestly can’t remember was nearly 5 years ago I put it together. I have some photos but doesn’t really help much. I just recall something in the spec mentioning they were floating

 

Looks from

this picture as though there

is a few mm gap at small end

Edited January 11, 2018 by Andy F

[Andy 105 1 Cars]

Evening,

 I have had a PEc Mi16 rod in my hands today along with Wossner Mi16 piston. PEC have made the big end width 24.5mm rather than the o.e 22.45mm. In other words , the PEC rod is crank guided At the other end, the small end with is 20.6mm which would give it 2mm of side play on an o.e piston and more like 4mm on the Wossner . In other words, the Wossner piston is not going to guide the rods.e or otherwise but PEC have ‘allowed ‘ for this by making their Mi16 rod crank centred and narrowing the small end to accommodate all comers on the piston front. This is a long winded way of saying that if your rods have a big end with of 24.5 mm you will be fine, as the pistons will most certainly not trying to centre to rods. 

[petert 586]

9 hours ago, welshpug said:

Why an 8v rod also?  with its shrink fit pin and otherwise same length, but a much wider small end.

 

 

Order an 8V rod with a Ø22 full floating pin, is what I meant. Or get the local machine shop to bush them. The width of the small end isn't an issue in an aftermarket piston. Look at my pics above. The washers are typically 2mm thick each.

Edited January 11, 2018 by petert

[Andy 105 1 Cars]

Andy,

As you suggested, whip the sump off, and check the width of a big end ( remove a cap if you need too) . From your photographs, the rods clearly and not piston centred, so  as long as they are crank centred ( ie 24.45mm) you will at least know that the rods are going to behave themselves . Peugeot seemed to use both options, depending  upon the engine, with crank centred being in the majority in the XU9/10 series as far as I can tell from looking at engine specs . If you really do want to keep to Mi16 spec and have the rods piston guided, Peter has given you advice which would sort the problem.

[Andy F 0]

Thanks for everyone’s help. There is a relatively simple solution in both outcomes. Will let you know how I get on.

[Kane 34]

Am I right in saying then that a Gti6 rod is crank centred which would allow a fully floating EW10J4S piston to be installed without any major concern? The small end of the Gti6 rod would need rebushing to 21mm and there is a very slight difference in the small end width between the two (Gti6 19.5mm & EW10 19.3mm). Would this 0.2mm cause an issue? 

[Andy 105 1 Cars]

The gti6 rod is crank centred , so the piston can float. On the gti6, Peugeot went back to the method they used on the xu9j2 and pressed the pin into the rod, but the piston floats. ( I have one next to me as I type). However, you will need to check the compression height of the ew10j4s piston. I think it is quite low as the rod is longer than the 158mm of the gti6. I am not sure about this , but recall I did look at the idea for my Mi16 . As for rod piston clearance, as you have to have your gti6 rods rebushed , it would be fairly straight forward to machine the journal width if required. I think it is usual to have a couple of mm if the piston is floating . 

Sorry that I am not being definitive . Miles will have chapter and verse on the ew10js rods and pistons

[Andy 105 1 Cars]

Me again. Wrong about the ew10j4s rod length ( 139mm) but right about the compression height (29.5mm) so with a rod length of 158mm, half stroke of 43mm and compression height of 29.5mm , that comes to 230.5mm with a gti6 deck height of 235mm , unless you are using a 96mm stroke crank in which case happy days