So I've got my motor tore down and I'm in the process of deciding on a shop to do the work at. I also need to figure out exactly what I need done, which is where you guys come in.

This is a basic rods/pistons build, stock head. The plan is I'll need:

• Hot tank block & head
• 0.020 or 0.040 overbore (depending on what pistons I end up with).
• check/measure crankshaft and bearings (line bore?), Pretty confident I can stay with the standard size as everything looked good coming out. I want to be sure, though.
• Mill block and head flat for MLS gasket.
• 3 angle valve job on the head since my current valves leak..

As far as what I'll need to have - Will a machine shop expect to have the pistons in hand when boring? I would assume so, right?
How about any new fasteners, I'll be using ARP main studs, will they need those when checking the line bore?

Am I missing anything here?
Any help is appreciated, thanks all.

 

Machine shop will most definitely need the pistons to set the ptw clearance.

I sent my block in with the ARP mains installed, they of course checked the line bore, but did not need to touch it. I had to clearance the studs a bit to fit the MBSP, so if you use one be sure to mock it up first.

They will also check the head, if your current valves leak you may need new valves and possibly guides as well. Any decent shop will check it out before they do the valve job.

Are you doing your own assembly?

 

I'll be doing my own assembly. I've been doing a good amount of reading and I think I should be able to handle it (after $300 or so in tools!)

 

They will need the pistons for boring and honing, and i would recommend having the rotating assembly balanced.

Get the block shot peened ( comes back like virgin cast iron, great for painting)

Always a good idea to get the main bores cleaned up on the line hone with the main studs installed.

 

Cool, thanks guys. Is there anything else I'm overlooking?

 

Ask them what all the key clearances are going to be, and what the tolerance will be...

...then measure them, or pay the machine shop an extra $100 to measure them all with you/in front of you

 

I just bought a digital caliper, looking at getting a set of real calipers. I should be able to measure everything but the bores with that.

Still trying to decide on buying a $150+ dial bore gauge, or just trusting the machine shop.

 

You need micrometers and dial bore gauge or two. Good equipment is fairly pricey, and takes some experience to use.

In the words of agent fox mulder, trust no one. Paying the machine shop to measure it with/in front of you shouldn't cost that much, and if the machine shop won't do it, go to another one...

 

Micrometer.. That's the word I was looking for when I said " real calipers " haha. Yeah I'm looking at a fowler set, probably not the best out there but they look decent.

 

You can buy a fairly decent micrometer for about $100 and an inside micrometer for another $100. Check MSC Direct.

 

Yeah, I've rebuilt a dozen or so engines without checking line bores, I wouldn't be too worried. Torque them dry (although with ARP's lube on the main studs) and check bearing clearances with plasti-gauge. Then reassemble with assembly lube. Do this for rods and mains.

And put your location in your profile, so any locals might be able to tell you what shops to avoid and what shops are recommended.

 

Good info Curly, thanks. Location updated, southeast PA.

 

You can go even cheaper than that. Depending on size you can get acceptable ones starting at ~$20. I did check mine against the certified gauge blocks at work to be sure since I was using them to measure the lifter length and lifter shim thicknesses. And they checked out. Of course that $20 0-1" mic felt nowhere near as nice as some mitutoyos and probably wont last nearly as long but they function properly.

 

So I spoke with a local machine shop who looked pretty good. They seem to do a lot of Subaru work and some SBC work.

They quoted me the following prices - obviously I don't have to get everything done if I don't want to.

Block cleaning $60
Bore & Hone $108
Resurface block $125
Valve job ~$250 "depending on the head"
Resurface head $72
Measuring clearances $45
Align hone $150 - He was really pushing this, stating that sometimes with ARP mains it ovals the bore.

So I'm looking at ~$800 for everything. I'm not sure if I want to get a valve job as I don't think there's any power gain in it, but I do need non-leaky valves. I'm considering just lapping the valves and calling it good (and moving that cash elsewhere in the build).

Does this seem to be on target?

 

I know very little about machining, but I do like the idea of "align hone". I just don't know if our blocks flex much after the head is torqued down to justify the $150. Does the machine shop have a "torque plate" with our head pattern?

 

Lapping valves is a joke. If they leak, lapping will not fix it for more than about 30 minutes of idling. If any leak, get the head rebuilt.

If you're running ARP mains, have the mains line-honed. If you are running stock bolts, don't worry about it. My engine line honed the mains since I was running ARP main studs. I also had the cylinder bores bored/honed with a deck plate installed.

My advice is don't cheap out of machine work, it's going to make the motor last. Do it once/do it right. I'm on engine 7 now and finally taking my own advice!

 

Also consider having the engine balanced. Especially if you will be using non-stock rods and pistons. There weights will be different, thus balancing will be a good idea*

I've built motors with stock pistons/aftermarket rods, not balanced them, and rev'd them higher than anyone else on this forum and the motor not have a bearing problem. But I can't say it was smooth, it wasn't. My new motor that isn't finished yet was balanced.

 

I'd say those prices look good to me. Definitely go with balancing, lightening my rotating assembly along with balancing made my engine super smooth as compared to stock. And yes, get the valve job.

 

Did you have the crank lightened or just lighter rods/pistons? If you had the crank modified, did you have the counter weights ground/knife edged? How much did you have removed?

When talking to a machine shop about lightening a crank, what should one request for a Miata crank which is going to see a mix of track and street? In other words, what is a reasonable approach which won't impact reliability or longevity?

Thank you

 

I would highly suggest leaving the crank alone. The counterweights are there for a reason, not for you to machine them off. When they balance the motor they may machine a bit off of them to balance it, but don't go machining them off to save weight off the crank, not worth it and significantly going to weaken the crankshaft.