I have a 2010 John Cooper Works. I have a compression leak at the head gasket. There is no cross-contamination between the oil and coolant but I have the leak just the same. It's not overheating though.

So here we are, I need to do the head gasket. With that said, I figure I am just going to replace the pistons and rods. I went looking for come forged pistons and it looks like it is common to find 70MM and 70.5MM. Am I right to assume that 70MM is the OEM piston size and the 70.5MM piston size is due to folks machining the cylinder walls while doing this project?

Secondly, the .90mm head gasket appears to be OEM size but 1.2MM is also equally as commonly found. Again, assuming this is for folks who have the head milled .3MM?

 

I figure I would ask further... since I intend to buy pistons, rods, and head gasket... what else should I be purchasing to do this project (Other than the obvious with valve seals, etc.). I just did the timing chain a few months ago so that is good to go.

 

Hi ! Kudos on taking this on. Before any recommendation, what are your goals for the build. Stay with OEM level of performance, be more robust at OEM level, add performance etc ...

 

This is not my daily driver... but I also don't ever intend to track or "race" this car. The build needs to be street legal (we have emissions here in Arizona). So, the overall goal is to get this car humming along with as much power as is reasonable for a weekend driver that can pass emissions.

EDIT - I should add that there is no hurry here. I have a daily driver. This is a fun car that also acts as my hobby.

 

To stay with oem exhaust, stay with jcw turbo, get a street legal tune, upgrade the intercooler, etc..

 

That is generally the plan. Luckily the JCW Exhaust flows better than the S Exhaust. I've already upgraded the intercooler. Staying with the stock air box and the JCW airbox has been proved to be more than adequte when paired with a high flow foam filter (which is what I have).

But I am still not 100% clear on what I need to purchase for the pistons, rods, etc. I think I need 70mm pistons and .90mm head gasket (assuming when I pull it apart, everything is in good shape inside). But what am I missing?

 

Okay - given your JCW platform and current desire -

I'd have some head work done ( just a little to remove some of the rough parts that have to much metal ), I'd also see about replacing the oil pump and even fuel pump. This, along with you doinig the timing chain, should address any of the major issues that can happen down the road.

Mike at ECS ( ECSTuning ) should be able to discuss options with you on the above ( https://www.northamericanmotoring.co...m&pmid=3039497 )

For pistons/rods etc ... It really depends on if you want to hone or bore a little over. I am not sure what the best pistons are for JCW staying at near stock performance ( ie what CR - I believe it is 10:1, but you could go lower if you want to push boost, as well diameter ). For this - I would check with Mike also, as it seems they sell oem parts ( https://www.ecstuning.com/b-genuine-...h/11257576973/ ) but you might be able to get a rod and piston set from Mahle, Wiseco etc for cheaper.

If you are going to do a tune, I'd discuss this with Lou : @Lou@Prototype-R Lou does custom tuning. He also can recommend piston/rod applications for you ( not sure if he distributes or not ) - as he deals with and builds mini engines to different specs.

Hope this helps

 

Good stuff, thank you.

Since I figure I'll go overkill and get forged pistons, I just decided I'll go with CP Carrillo. The only place I could find that sells them in the 10:1 compression ratio is Detroit Tuned.

So, I have the OEM .90mm already in hand. I guess I'll get a 1.20mm head gasket as well and return what I don't use in case I need to mill off .3mm

I really do like ECS. I've bought a ton of stuff from them for this car as well as my son's Mini and my wife's mini. I've never reached out to Mike though.

 

You can vary the head gasket thickness to fine tune the final CR depending on what CR the pistons are designed and if the head is shaved. I'd make sure you know what you want your final CR to be ( usually determined by what max boost you want. I don't know what the max boost for efficiency of the jcw turbo, but others on here will know ).

btw - do you have an lsd

 

only the factory optioned LSD. I have the original window sticker and they had the add for OEM LSD. My understanding is, the OEM LSD is not the greatest.

 

Carrillo Pistons are top notch. As are the rods. I believe they come at a CR of 10.5 or 9.5 unless you can get a custom set made. So you will adjust your head gasket accordingly to get to where you want to be. Lots of posts around this theme. Higher boost tend to 9.5, lower to 10.5 ( this is where feedback from a good tuner will help given advance, total boost etc ). But IIRC, stock on the JCW is 10.0. So you have some design choices to make

 

Detroit Tuned brings them in custom in 10:1

https://www.detroittuned.com/mini-co...-n14-n18-10-1/

 

Cool - I see they say that they are the only ones with a 10:1 CR. They also take great pains to say it is only for an 'S' model - but not sure why ( different strokes ? )

 

Yea I've reached out to them via email to see the deal is with the language on that page... its a little foggy in my opinion.

 

... Not just sells!

I found this posted on here - a cut and paste from Bentlys.Bentleysough appears stroke and bore are reversed :

Bore x Stroke mm (in)
N14 MCS - 85.8 x 77 (3.37 x 3.03)
N14 JCW - 85.7 x 77 (3.37 x 3.03)

Comp. Ratio
N14 MCS - 10.5 : 1
N14 JCW - 10.0 : 1

So looks like stroke is shorter for JCW.

 

Once upon a time, Forums like this one where were engine builders would be available to talk about these things. Sadly, Facebook "groups" have all but killed the forums and those groups are a total **** show for trying to get REAL information.

That said, I've been compiling information into a spreadsheet on the N14B16C (JCW Specific N14 motor) and everything I've found says it has the same stroke as the N14B16B and N14B16A (which is 85.8). And all Prince motors share a 77mm bore from what I've seen.

I really do wish I had better access to someone who has built on the N14B16C to ask some direct questions.

 

Hello,
You have been email me about the Pistons we make. we are also a full service shop ans build a lot of these motors so we have any answer you might need. P.S. i think they stock head gasket will be fine unless that head is extremely warped. its rare that most of our builds need a thicker Head Gasket.

https://www.detroittuned.com/mini-co...-n14-n18-10-1/

 

TIgger is active on here, discussing multiple engine builds. Here is one of his earlier ones:

https://www.northamericanmotoring.co...ger-2-0-a.html

General mini talk might not get the most response for your questions - as this is more a 2cd gen engine/mod/hatch topic

 

I believe Carrillo makes these pistons for you ( vs you manufacturing ). Do you have in stock or is this a build to order. Also - can you say these would work in a JCW vs only S? Is the stroke really shorter for the JCW vs S? Is that how they lower the CR? If so, do they use shorter rods for the JCW with these pistons ?

The topic on the head gasket is not to address a warped head, as the OP might shave and square it. It is more for fine tuning the the final CR

 

Detroit Tuned and I have been emailing. The Pistons work on both JCW and S. They have stock of those Carrillo 10:1 pistons according to Detroit Tunned emails I've got.

I've looked all over to varify the stroke and everything I've read tells me the stroke is 100% the same between the S and JCW.

 

Looks like you got it nailed - Kudos !

 

Week after thanksgiving I'll be tearing the head off and we will have a better look at the condition of the head and we can make make some better decisions on what we are doing with the headgasket.

 

As noted bore and stroke are the same. The only difference in the blocks is the JCW has some thicker webbing in places, and the heads are identical. The only reason to increase head gasket thickness is if the head and/or block are skimmed. If only a couple of thou and keeping the stock cams I wouldn't worry about it too much. No real way to know until everything is measured for true and the machine work is complete. Ask the machinist to record material removed if it becomes necessary. The custom pistons Detroit Tuned had made are very nice, retaining the tear drop for DI spray swirl and the larger exhaust pockets needed for the N18. It doesn't sound like it's in your plans but if going with high lift cams I'd absolutely try to maintain the correct height and also make sure you have sufficient valve to piston clearance when assembling.

I'd also recommend looking into forged rods since you're already going to be that far into it. Detroit carries Carrillo, Supertech and other less expensive options as well. Adding the rods should make the bottom end pretty much bullet proof for your plans and should provide lots of smiles per mile for years to come.

 

For Pistons...Forged for sure...
AND...

I really recommend against ANY piston made with 2618-alloy.... Just not appropriate for a street engine.

4032-alloy, or a similar higher-silicon-content alloy... like the proprietary alloys from Mahle and others... would be the most appropriate for your build.


My 2¢ FWIW.

Getting a machine shop that can give you the correct hone (it's quite challenging to find one that can give you consistent RVk and RPk numbers with the consistent cross hatch)... the days of being able to use a ball hone, or an older Sunnen swing-machine with mineral stones... and call it good are out the door, if you want good results.....

Good Luck with your build and keep us in the loop !






.

 

The more I learn, the more I learn that there is more I need to learn! (And I've been turning wrenches in my garage for 20 years).

Thank you for this info... seems the alloy isn't necessarily readily available info on some of the products I am looking at.