Help-engine expert builders
 

racingmazda motor, 2.0L forged internals, NON-STROKER, just bore.
1999 miata head, ported/polished, stock valvetrain, high revving valve springs, stock cams with adj. cam gears.

started the car for the first time, it started but there was a faint valvetrain noise. Removed the valvecover and it sounded like the pistons, were hitting the valves juust slightly. Retarded cam timing -4 degrees on the intake cam and the noise went away.

I'm baffled, because the pistons are not domed, they are low compression 9:1, the block as far as i can tell wasn't decked, nor was the head. Stock type head gasket was used.

Any ideas? Any suggestions?
Someone had suggested that maybe one or more of the pistons were installed backwards where the recesses are deeper for the intake valves, so if backwards it would obviously hit.

I don't think either head nor block were milled at all, even so, i wouldn't think they could be milled to the point of touching valves.

I'm going with the valve recess orientation on the pistons. Not so much the indention, but the fact that the larger intake valve won't fit in the smaller exhaust recess.

Did you rotate the engine by hand before starting/cranking? That saved my ass on an engine that we did a massive head deck on to get 10+:1 compression with stock parts (rules).

first things first. I've never seen any engine survive even the slightest of piston/valve contact. if this happened you are extremely lucky. second thing. . . fire your engine builder. all of these things should have been checked before final assembly.


"I don't think either head nor block were milled at all, even so, i wouldn't think they could be milled to the point of touching valves. "

it's not realy a matter of decked or not. if the cam timing isn't right you can easily push a piston into a valve.

Factory Miata engines are non-interference.

However, I have never built a stroker so I don't know if the extra "dwell" time from the longer stroke will cause the Miata engine to become an "interference" engine.

Take off the head and show us pics of the block.

it's not a stroker.
just a bore

yes, however he did change the pistons.

take the head off put some puddy on top of hte pistons then set the head back on tighten the bolts slightly then rotate the engine. Take the head off and look how far the valves went down into the puddy at both settings of cam timing, instant way to tell.

...or just look carefully for contact marks on the pistons and valves when you remove the head...

That wont tell him how close it is coming though i have seen engines clear when cold and when started and warmed up collision occurs.

Hence the "FACTORY Miata engines are non-interference".


Robino, I think you need to check the tappet (lifter) clearance. If you don't get the shims adjusted just right you will either burn a valve (tight exhaust) or hear a tapping from the loose setting.

Go with the easy stuff first...don't assume the worst.

I posted here some time ago the settings for the tappet adjustments for the late model heads...run a search.

They can be a bitch to set up right because of the need for just the right size shim.

where in south FL are you?
car is down in Davie/right behind Costco/Carmax parallel with 595

if you're not to far, maybe you can swing by and take a look with me.
I'll take a peek at the piston tops with a tube cam through the spark plug hole to see if they're backwards. If not...???

i hear what you're saying, but would the noise have gone away the moment i retarded the cam -4 degrees? Had it been a mis-adjusted lifter?

we can sit here and argue semantics all night long, but that isn't going to help the guy is it? we aren't talking about a factory spec engine here.

now that being said I think it would be a good idea to tear the head off and investigate further. the putty trick is a good one. another thing you can do is remove just the cams and push down on the valves while you have the piston at tdc just for a prelim to check clearance. if you wanted to get nice with it you could also toss a dial on there.

Sorry man, I wish I can take a look at it, but I am swamped with work through Saturday.

If you are still having problems when I am in the area, I can swing by.

Sorry, I need to read the posts better...yes, you are right, if the noise goes away when you retard the cam then, it's not the tappet clearance issue.

I will be a little more candid here than I was on miata.net. Brian Stoid probably built your motor and he's a fucking crook. A certain dallas shop had a motor show up that had the head and or block decked and the pistons hit the head and fucked everything. Take the shit to court, you were fucked. That shop does this shit over and over...use John Day. He's a god.