One vehicle runs, another decides it needs a new motor

Chad Culbertson · **Posted:** Mon Nov 23, 2015 11:42 pm

So, i've been noticing a bit of a rattle in the miata between shifts and neutral loads on the engine in the 3k rpm range on the Miata. It also has some audible knocking on cold startup. I did a bit more closer inspection tonight and it looks like cylinder 2 has a problem. It sounds like rod knock and removing spark to that cylinder makes the sound more muted, but removing spark to cylidner 1 changes nothing. It's a nice solid sound too, which makes it even more likely to be bearing knock and nothing else. It goes away with either decel load or accel load on the engine.

103k miles and this motor is done for, I guess all the abuse finally caught up to it, too bad it wasn't my abuse or I would feel a bit better about it, lol.

Since I caught it early enough I might be able to just yank it out and throw some bearings in it assuming everything else is in decent shape, but it's certainly going to be parked for a bit until I figure out which route to take.

Such is life I suppose, at least the parts are usually cheap for these things, much cheaper than a Camaro, lol.

Cash Davidson · **Posted:** Tue Nov 24, 2015 8:47 am

I think my dad used to tell me if it knocks at an idle - its a crank bearing. If it knocks under load - it is a rod bearing. Or maybe it was the other way around - I guess I really have nothing helpful to offer. :roll:

I hate if for ya - good luck.

Cash

Chad Culbertson · **Posted:** Tue Nov 24, 2015 10:54 am

The motor was pretty leaky anyway, so I had already contemplated pulling it out to get new gaskets on it anyway.

Since I seem to have caught it pretty early on and it hasn't exploded then I may be able to just do a cheap rebuild on it and slap some bearings in. Probably do a compression check and if compression is good pull some caps on the bottom end, make sure nothing is scored that would require machine work and just slap some new bearings in there and rock it.

Jordan Normark · **Posted:** Tue Nov 24, 2015 12:45 pm

I rebuilt the bottom end with .010 over bearings after rod knock on my Miata shortly after getting back into autocross in 2012. I upgraded the oil pump gears and shimmed the relief spring while I was at it. Low oil pressure is common on those engines. Your oil pressure is likely low especially with bottom end wear. Also, check your cam shaft journals by pulling a couple of caps. The aluminum surface of the head journals wear quickly in the absence of good pressure and you may be surprised by how much. If there is significant journal wear in the head, it may make more sense to look for a good junkyard engine since the cam journals don't have replaceable bearings.

Chad Culbertson · **Posted:** Tue Nov 24, 2015 3:42 pm

Jordan Normark wrote:

I rebuilt the bottom end with .010 over bearings after rod knock on my Miata shortly after getting back into autocross in 2012. I upgraded the oil pump gears and shimmed the relief spring while I was at it. Low oil pressure is common on those engines. Your oil pressure is likely low especially with bottom end wear. Also, check your cam shaft journals by pulling a couple of caps. The aluminum surface of the head journals wear quickly in the absence of good pressure and you may be surprised by how much. If there is significant journal wear in the head, it may make more sense to look for a good junkyard engine since the cam journals don't have replaceable bearings.

So what's the best fix to make sure you get good oil pressure on these? If I yank the motor out or pickup a used one I want to make sure it'll have good oiling, i'm guessing the upgraded gears and shimming the relief spring helps with that?

Jordan Normark · **Posted:** Tue Nov 24, 2015 5:25 pm

I went with billet oil pump gears mostly because I turn the engine close to 8,000 rpm, but the replacement gears do have a different profile to them designed to pump more oil. If you plan to keep it stock I wouldn't bother with replacing the gears. You can shim the oil pump pressure relief spring using a couple of washers. It's been a while since I read about how much to shim, but it was well documented on Miataturbo.net If I remember correctly, I used 3 washers ~4mm with a new pump, gears and sanded housing (tighter clearance between gears and cover) and bottom end rebuild. Hot oil pressure runs 25psi at idle to 85psi at rev limit.

RobLupella · **Posted:** Sun Nov 29, 2015 8:36 pm

I have a 1.6L motor with a crap ton of miles on it. Free to a good home LOL

Chad Culbertson · **Posted:** Mon Nov 30, 2015 11:44 am

RobLupella wrote:

I have a 1.6L motor with a crap ton of miles on it. Free to a good home LOL

That seems a bit backwards.... lol.

I pulled some cam caps this weekend and they look fine, no scoring or anything I could see. Obviously you could see some "polishing" from the use but the cam journals and caps had no actual scratches with depth or anything.

So likely it didn't starve for oil at any point, who knows why the rod bearings decided to wear but it did. I'm going to do a compression test and if that checks out the plan is to just pull the motor and slap some new bearings in it. I see no point in spending the money on a full rebuild or putting some junkyard motor in it if the top end is good. I've re-bearing'd a motor before and last I heard it was still running strong.

Chad Culbertson · **Posted:** Wed Dec 02, 2015 11:42 am

Made some video from mounting the go pro under the hood, it's pretty easy to hear from the Camera, but it's almost impossible to even hear with the top down.

https://www.youtube.com/watch?v=o5XUHfUm05U

Chad Culbertson · **Posted:** Thu Dec 03, 2015 6:15 pm

If it turns out to truly be a bad bearing there's a really good chance this guy is getting a VVT swap. I found a fairly cheap 01 motor at LKQ I might pickup to throw in it, and then I just need the VVTuner controller to run the VVT and i'll be all set.

Jordan Normark · **Posted:** Thu Dec 03, 2015 9:08 pm

Sounds like the beginning of a CSP monster

jeremy gast · **Posted:** Fri Dec 04, 2015 11:52 am

Chad Culbertson wrote:

If it turns out to truly be a bad bearing there's a really good chance this guy is getting a VVT swap. I found a fairly cheap 01 motor at LKQ I might pickup to throw in it, and then I just need the VVTuner controller to run the VVT and i'll be all set.

I went ahead and bought this engine. If you want it let me know, if not I am gonna use the bottom end on my purple car. It was cheap enough I didnt want it to get missing.

Chad Culbertson · **Posted:** Fri Dec 04, 2015 12:40 pm

jeremy gast wrote:

Chad Culbertson wrote:

If it turns out to truly be a bad bearing there's a really good chance this guy is getting a VVT swap. I found a fairly cheap 01 motor at LKQ I might pickup to throw in it, and then I just need the VVTuner controller to run the VVT and i'll be all set.

I went ahead and bought this engine. If you want it let me know, if not I am gonna use the bottom end on my purple car. It was cheap enough I didnt want it to get missing.

Do you want the head? If you wanna keep the head then i'm probably interested in the bottom end. I'll just slap my '00 head on it and run 93 octane.

Whoops, mis-read that, lol. Let me see what the oil looks on my car and find out for sure if my bottom end is bad. My other option is I found a bottom end at a place clsoe to Wilson, but who knows what shape it's in since the head got removed from it. They have it listed at 350 bucks and it's from a '99 so I assume they must believe it's a good bottom end, no clue on miles though.

jeremy gast · **Posted:** Fri Dec 04, 2015 1:28 pm

Ya if I use this "lkq" motor I am gonna use the bottom end and just slap my head on it.

Which company in wilson?

Chad Culbertson · **Posted:** Fri Dec 04, 2015 2:45 pm

jeremy gast wrote:

Ya if I use this "lkq" motor I am gonna use the bottom end and just slap my head on it.

Which company in wilson?

Cox Auto Salvage in Elm City, it's just a bit north of Wilson. I found it using car-part.com but it doesn't have any mileage or grade listed.

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