7 replies to this topic

[Tom Neel]

I just bought a motor that was suppose to be fresh and ready to go from someone that had a good track record however after recieving the engine and performing a leakdown test the bottom end is leaking 20 percent in three cylinders..The head was just redone by a proven engine provider and is perfectly sealing. Infact the cylinder head has not been run since being refreshed. My question is can you use aftermarket piston rings or are we only allowed to use mazda rings? Thanks in advanced for your input. I just want to make sure the engine will be legal..

[Jim Drago]

Mazda ONLY Tom

[Dave D.]

Was the engine sitting for a long period of time? Could there be some corrosion in the cylinders? I know Porsche engines leak down very poorly when cold. I only pay attention to leak down numbers from a warm engine, unless something drastic is going on.Sticky rings? Did the numbers change a little bit if Vaseline or motor oil is smeared on the cylinder walls?

[Tom Neel]

Dave D....Engine has been sitting for a year...If I see an engine that gives low leakdown numbers from the rings I normally put atv fluid in the cylinders and spine the engine over several times to see if it will free up a sticking ring..this did not solve the issue with the engine..it helped very slightly but at 18 percent it still needs to be rebuilt..I sell used miata parts for living and I do compression checks on every engine I sell before we put them on the shelf and before we ship them out to make sure they are good..Even used engines sitting on my shelf for months don't have these kind of numbers..at least I wouldn't sell a motor to a customer with these kind of numbers..I'll have the bottom end apart after lunch today....hopefully everything will measure out and a quick hone and new rings will get everything back sealing good....happy holidays! 

[Dave D.]

Gotcha, Sounds like you've got it covered.

[Ron Alan]

I've heard of overbored blocks being fitted with stock pistons...no idea if this was intentional or not but it made for pretty big piston to wall clearance...but the motor made acceptable power. But I would think in this case leak down would not be so good? Maybe check first?

[dstevens]

You can use over rings with stock pistons if it's bored, mine is.  I've said this in another thread but the Mahle and Clevite internals I used in mine were stamped the same as what came out of the engine.  It's typical that a manufacturer doesn't make parts like bearing or rings and will get them from a supplier.

[Brandon]

My own personal experience with aftermarket rings (due to a supply problem at Mazda Motorsports): there are only two aftermarket suppliers for Mazda 10-over rings for a NA1.8 and my builder noted the set I bought were too tight for his preference.  They're now in a box sitting on my shelf and probably forever doomed to sit there.

 

Regarding any indicators/stamps on the rings of a Miata engine?  My builder has never seen anything across the board of engines he's disassembled.  Profiles & thicknesses may change but outwardly visible differences are non-existent.