pics maybe next week....



so i ended up rebuilding a 1990 miata engine, because mazda couldnt do it. 1990 1.6 motor, with 200k miles on it, it did the tradiational miata thing. the key way on the older piston engines is teeny, and it breaks, so the timing belt pulley ends up being off, etc etc.



i put a new bigger crank, oil pump and big pulley into it. plus new pistons, rings, bearings etc etc.



so anyways the car comes back, and it smokes. we did send the head to the machine shop, but we're not sure the valve seals were changed (we dont know what they did), and also the point of the post.



the exhaust cam bearings are scored up. there are 6 bearings, and only the 4th and 5th ones are bad, why?



is there something i did? or is it some peice of sand from the machine shop? any ideas would be helpful....



car went maybe 1000miles, everything else looks good....

 

Okay, okay, okay, okay. Friend of mine at NTI (Nascar Technical Institute) just bought an LS6 on Ebay for (wow, copywrite infringement) a song because a head was blown on it. He took it apart and found the hatch marks still on the cylinder walls, it only had a couple thousand miles on it if that. He checked the heads. It had the same problem as what you just described. I think it has to do with either the way it was put back on, i.e. bad studs(?) or the deck was not flat. Check the two surfaces, the deck and head. Also, make sure the bearings are kosher before they go in. Little stuff that counts - Tyler gone -

 

I'd study the oil galleries and see if there is a way that gunk in a passage could have found its way to 4 and 5 and only 4 and 5.



After making sure that the cam caps were installed where they came off from. Being unfamiliar with the B6 engine, I do not know if this is possible.



Then I'd check the cam for straightness. Camshafts like to roll off of benches, donchaknow. Did you meaure the journals vs. the bores?



Don't feel too badly about it. We just put a hot-rod engine in a work van. Very pain in the *** installation. Drove it around a bit, goofy grins all around: something definitely not right in this picture! Doubling the power output does strange and incongruous things to the demeanor of a van. Putting the new custom exhaust in it, noticed that it has a leak from the front seal. On a hunch, I checked crank endplay. .021". It was not like that when we put it together. Now the engine has to come back out, along with the transmission this time...





Tyler (is that your real name? ) it should be noted that for most newer cars, the crosshatch stays a long time. We pulled the head off of a 22R engine with three hundred thousand on it and the crosshatch was still very visible. Same for a 230,000 mile Buick 3800. The days of blocks cast from Silly Putty are long gone.

 

yah it seems like something got into the cam oil galley, i'm thinking its the machine shop, cause i only touched the head to put lifters in it and put it on the motor...



the cam caps are labled 1-6 with an arrow pointing front, thumbs up for that....



exhaust cam was actually new, if you ever build a mazda b6 or bp engine the fsm tells you to tighten the cam caps from the centre outwards (like the head bolts), which snaps the cam....



yeah so i guess we'll see what the machine shop says on monday...

 

where are them pichers....

 

I think you're right; machining debris. Quite common.



However I hate to say it, its you're fault for not cleaning it. I've never heard of a machine shop completely cleaning after doing machine work; sure their will not be big chunks, but lapping compound etc is usually always still there. Its just not usually visible by just looking at it.



I'd bet if they did valve work, their going to leak badly in under 5k miles.

 

We do a lot of machinework at our shop, have lots of nice yummy expensive engine-specific CNC gear and such.



EVERY cylinder head, engine block, crank, piston, bolt, everything gets completely disassembled including all of those annoying thread-in or press-in gallery plugs, cleaned, bead-blasted if necessary, cleaned, machined, and then thoroughly cleaned and dried, including rifle-brushing out all galleries and blowing everything out with compressed air, then cleaning AGAIN.



It is time-consuming. Time-consuming means expensive. We've never been accused of being cheap, but we've also never been accused of doing anything but top-notch work, so people don't mind.



Lapping valves is a sin, by the way. If your tooling is accurate, and your guides are in good shape, you will get a perfect valve seal between a perfect valve and a perfect seat. Lapping can and will only make things worse.



If your tooling is inaccurate, or your guides arew wasted, you're better off just putting your money into a pile and burning it. Bad guides will lead to valves coming apart.





I am not sure what all of this has to do on a rotary-based website, except perhaps to serve notice that rotaries really are cheaper and more reliable, and a good deal more pleasant to work with.

 

this is the engine failure section! i had an engine fail....



but yeah i pretty much pulled the head out of the bag and put it on.... and if i would have known they weren't going to change the valve stem seals either i woudnt have even sent the head out.