Doing a low budget N14B16A engine rebuild with scratched cylinder wall on my 2009 mini cooper S and this is my first time dealing with machine shop. They said honing is not enough and they need to bore it. I bought them the cheapest 0.25mm oversized pistons (77.25mm) I could find on ebay. They called and needed the specs for the pistons - the piston to bore clearance. Ebay listing does not say and seller is not answering. I certainly don't want a newly rebuilt engine knocking or seizing up.
Is there a "normal" clearance for these cheapo pistons? I prefer not to spending hundreds more $ for some brand name pistons for my old beat up mini.


rsized pistons from ebay for $130. The

 

When you get the pistons in. Take them to the machine shop. The shop will measure the piston and the bore. They have the micrometers to do the job. Then they set up the machine and take what is needed.
If this is the first time dealing with a machine shop. Let them know and ask them what they need to do a good job. Most the the machinist that I know are honest and are willing to work with you.
It's the guy that comes in and they think they know more than the machinist that drives them crazy and then they do the work just as the guy wanted it.
When the guy that knows it all comes back and complains, they just show them the work order.
Talk to the machinist and be honest. You will have a better machine shop experience.

 

The machinist insisted on me getting the specs (at least the clearance) from piston manufacturer. Calls going back and forth between me and him and I also messaged the ebay seller numerous times. Seller was helpful but could not get me the info. I see those expensive brand name ones that are $800 are with specs but none of those $140 ones on ebay has any info. Seller told me he has been selling them and never have anyone demanding such info. I do believe him. I googled around and see that typical clearance for 77mm bore turbo stock engine is about 0.003" to 0.004" and I told the machinist let's go with 0.004" that and he said it is weird and thought the ebay seller just threw the number out. I asked him to suggest what to do and he said he would do 0.011 ish... The piston has coating. I will have no choice but to trust his suggestion. He is an old school guy running the shop for decades. I don't have many choices of machine shop here in San Francisco bay area, particular near me in Fremont.

 

Find a new shop. The spec for total wear is 0.13mm or 0.005", assuming the material is the same as the OEM pistons.

Here are the OEM build specs:

 

The pistons are 0.25mm oversized and they have coating. newtis.info does not really have much info about that. I want to use this machine shop in the future. I will give them a try and when I have update, I will report back. If I don't, pls message me. Hope I will have a running mini cooper by next month.

 

Engine runs ok now.
Machine shop figured it out. They should not have asked me too many questions.

 

Any update on these ebay pistons? Considering then myself.

 

Any update on the ebay pistons? Im considering some myself.