ITT Dieselmiata asks stupid questions about engines.
 

Disclaimer: This is my first 4-cylinder "modern" engine built. My history with engine rebuilds consists of old pushrod V8s.

Over the last year, I've been slowly building a spare engine to replace my tired 190,000 mile one. I got the engine installed over the last weekend started the break in process. She sounded normal, lots of HLA noise until she got pumped up but after about 30 minutes of run time, it developed a loud knocking/rattling sound that is only audible upon acceleration. Even stranger to me, is that she decels slowly and smoothly until 2000 rpm when she drops suddenly. I don't think it's a rod issue, as it sounds to be coming from the head.

Stupid question #1. Are the wrist pins directional? I put forged rods in and they went in pretty easily, but I did not check the clearance between the wrist pin and the piston holes.

Stupid question #2. Would several collapsed (or not properly primed) lifters cause the running issues? I know they make hellish noise, but I can't figure out the rpm drop.

I did use almost all OEM Mazda parts. My pistons are OEM used from another engine, but they were in great shape and measurements checked out. The block and head were baked/blasted/inspected by a local (very reputable) engine build shop and given the green light.

I know my oil pressure is good even though I my pressure gauge reads low. I left one side of the oil feed hose disconnected when I started her once, and now have oil stains on the ceiling.

Any insight or cat pictures would be appreciated.

Sounds like something loose in there. Did you torque all the big ends properly?

Yes, I'm pretty ---- about torquing bolts. I like to torque them once, then use a second torque wrench to verify.

I read that to check lifters you can slip a .025" feeler under the camshaft lobe when it is 180* out, and if it fits easily the lifter is bad. It this correct?

Drain the oil into a clean container and then strain it though some cloth to look for metal.

Pistons are directional. Wrist pins and rods are not.

Lifters don't just make noise under acceleration. They always make noise. Rod bearings and a few other pieces make more noise under a load and much less without a load.

What were your rod bearing clearances when you assembled the engine?

I wrote them down, but I don't have the paper in front of me. They were all within range of the FSM, I do know that. If memory serves, they were all about .0010

Big ends. Sad face

ITT Dieselmiata asks stupid questions about engines.
 

Well, lifters are all good. All stiff as boards and no gaps. However, the oil looks like this:
Attachment 143968

Which leads me to stupid question number 3. How the hell can you wipe a bearing on startup of a fresh motor?

Something was wrong. My guess is a main bearing was installed wrong and not getting oil.

You're not alone. I got 10 hours out of my re-build this spring. The builder is doing it again with no labor charge, parts only.

Needed more lube :dunno:

https://www.miataturbo.net/attachmen...ine=1436405628

ITT Dieselmiata asks stupid questions about engines.
 

Last time I trust a cat to install my engine, that's for sure.

That sounds familiar... Mine did have same kind of noise under light throttle and it got a lot worse:

Found the problem. This was laying in the oil pan when I took it off.


https://www.miataturbo.net/attachmen...ine=1436495797


Yup. That's the thrust bearing. Fun times, fun times...

That sucker looks pissed off!

Any idea how that happened?

I have no idea. Everything was installed per the FSM and torqued to spec. I mean, it's pretty hard to screw up installing a thrust bearing. Maybe it was machined wrong or the wrong size?

If that's the case, I guess I was asking for it. I trusted the size marked on the box and didn't measure it before installation.

I just hope it didn't destroy anything else.

Did you measure crank end-play? How did you install the thrust bearing (ie before or after crank was set into engine)?

I installed it in two parts, I laid the first half in it's journal and then laid the crank. The other half was laid in as I put the #4 main bearing cap on and torqued it down. I have the end play wrote down somewhere here, but it was within spec so I continued on.

On the positive side here, I just gave the engine a good visual inspection and can see no damage to anything else. I'm going to pull the rods and pistons this afternoon to see if I have to start from scratch or can salvage this build.