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I don't have much to add other than saying that those temperatures are regularly achieved on track by both stock cars like spec Miata and higher power boosted Miatas as well. Quality synthetic oil is fine up to nearly 300F, modern engines like the Ford Coyote run 260F+ all the time even with massive coolers, and 220F coolant is not really a huge issue either. Definitely not enough to cause a meltdown.
Also for the rebuild, keep in mind if you'd like to make more power in the future, smaller diameter piston bore means thicker cylinder walls, thicker cylinder walls means stronger block.
My block is already at 84mm with scored bores. I need at least an 84.5mm piston, but would like to go up to 85.0mm for the extra displacement. If I have to buy a new block, I'm going to loose my mind.
When I had to rebuild my motor after a throttle body failure a few years ago (wow, closer to 10 years at this point now that I think about it) it was cheaper to buy another block than to pay the premium they were charging at the time for 84.5mm pistons. Dunno if that's still the case though.
I have also read that not all blocks can be bored that large, some of them will break into the water jacket.
Carrillo A-beams are great, I've been very happy with mine.
Once again, I agree with the guys Ken: unless you intend to sonic test the current block, you probably don't want to hog out a block you are planning to keep for a long time.
It's a crappy situation, and often times people call it excessive, but in the business of engine building you really gotta have everything perfect to meet the standard you're setting.
I'm definitely seeing the light here. My engine builder is giving me a fresh OEM block to bore out to 84mm. I have ordered 9.0:1 CP pistons, Carrillo A beams and ACL Race bearings.
For those asking about various measurements in my engine. Attached in the blue print from my build. My engine builder is Tom McCulley at https://mccullyracingmotors.com/ His website is geared toward Ford V8s, but he builds plenty of BP engines as well.
Perhaps I'm looking at this from the wrong perspective, and given my lack of engine building experience I don't want to throw around any accusations here, but first impression seems like some of those measurements are "too round". Just from a Gage R&R perspective, with micrometers that read down to 0.0001" (which I'd like to think is common for master engine builders), I'd probably expect more variation for items like the bearing and piston to wall clearances.
Looking specifically at the wrist pins, and pulling from 5X's product pages, if I'm reading things correctly the called-out clearance would be 0.0011" not 0.0005" (0.7881" rod wrist bushing bore dia - 0.787" wrist pin dia). Gut feeling, 0.0005" of clearance seems like a rather tight/almost transitional fit, but I could certainly be wrong. Perhaps someone else can chime in if they recorded their wrist pin specs from a previous build?
Anyway, just food for thought. Best of luck with the new build.
Last edited by Spaceman Spiff; Oct 12, 2021 at 10:52 PM.
After reading the links 18psi kindly provided, I'm getting frustrated. Pulling out my soap box. Most businesses in this country have sold our soul to the Chinese Government. In the name of cheap labor, we have endured **** quality control from those unscrupulous slanted-eyed, commie bastards. They will think nothing of providing samples of a product exactly as specified, only to later substitute lower quality materials to save themselves money and not alert, or lie to the US customer. Manufactured in China has fucked me on my valve stem seals, my pistons, my rods and they are currently ******* me with storage batteries in my day job. Rant over. And if I offended any Chinese people, get over it. If you don't know every word above is true, you're an idiot.
A truly appreciate everyone's input on this issue. I will check with my engine builder on the roundness of my cylinders, but I doubt this is the issue. He is an ASE Certified Master engine builder and has built engines his entire life. Unless more information presents itself, I'm thinking the wrist pins broke because of ****, Chinese material. This created heat in the bottom of the piston causing the failure. I'm buying 100% American parts to rebuild my engine for the second time. I'll be buying Carrillo A beam rods.
Now I have to find pistons. My block is already at 84mm with scored bores. I need at least an 84.5mm piston, but would like to go up to 85.0mm for the extra displacement. If I have to buy a new block, I'm going to loose my mind.
...first impression seems like some of those measurements are "too round". Just from a Gage R&R perspective, with micrometers that read down to 0.0001" (which I'd like to think is common for master engine builders), I'd probably expect more variation for items like the bearing and piston to wall clearances.
Right on the money. 90% of "blueprint" or "spec" sheets I see online are garbage. As someone with a metrology and engine building background, I get incensed by these things. Regardless of the called for tolerances in this specific application, there's a number of red flags:
1) Piston to deck height only provided on piston #1. These heights are NEVER identical across all pistons unless you specifically mill piston tops or take other action to make them so. This tells me the others were never checked. Granted you're running an exceptionally large piston to head clearance so I wouldn't anticipate issues, but it certainly is indicative of the lack of attention to detail when the entire task is inherently based in detail.
2) Bearing clearances provided with .001" resolution..0025" and .0034" round to .003" but are very different in terms of bearing fit. Same thing with piston to wall clearance.
3) Literally zero variation cylinder to cylinder anywhere on the sheet. This is not possible in reality, no way, no how.
I'd like to see all of these measurements taken again as part of the post-mortem. Your "engine builder" may have all the credentials to absolve him of any blame in your eyes, but these numbers are all fabricated. Someone probably eyeballed most of them to be "close enough" and filled in the ideal numbers to make you feel warm and fuzzy about the build sheet. The fact that you got 5 years and 50,000 miles out of this engine is astonishing already.
twopointwo..... this is a great quote: ...but it certainly is indicative of the lack of attention to detail when the entire task is inherently based in detail.
Is the crankshaft still in the block or has crank been removed and shortblock completely disassembled? If its still in the block can you measure the thrust clearence? If Its removed how did the two thrust bearings look?
Something extraordinary happened in that engine to snap 3 out of 4 wrist pins. Whether the root cause was manufacturing defect, assembly error, or (hard) usage has yet to be determined. To @twopointwo 's point, the builder spec's can be questioned and a reality check there can help the OP identify a possible root cause.
I'd like to know what kind of forces (dynamic and static) would destroy a wrist pin like that - out of curiosity. For me, that's something that just doesn't happen. I would expect a piston, or rod to fail well before a pin would snap in two. For me, that points to a manufacturing defect - just my $0.02.
I won't get into whether or not you actually had those measurements, but personally your rod and main clearance is too large, I usually see under .002" for both, you're at .0025 main, .003 rod. I've never an issues for me to desire larger clearances. Except the ridiculously low oil pressure of a BP, especially at idle, which would only be exacerbated by larger clearances.
Ring gaps look ok. Maybe a few thousands small on the top ring, few thousand small on the bottom ring. I did .019/.022, but that's cutting hairs at that point.
I would NOT run ACL race bearings if you are not racing. IMO there's too much debris in the oil of a street driven car for the race bearings. I would even suggest stock bearings if you raced it. Some of the quietest (knock), cleanest (inspecting cut open filters), and highest HP builds I've worked on (330, 320, and 360hp) have all been stock bearings. Love your choice in rods and pistons though.
I have a set of pistons laying around here with identical damage from crap machining; an ovaled bore and too tight clearance. Possibly end gaps too tight as well.
I would lay the blame on the machinist, especially given their demonstrably false “build sheet”.
Personally, I’d be inclined to believe that the pins broke as the pistons seized in the bore at TDC/BDC.
Of course, this thread makes me not have much sympathy for you…
Way to show your true colors Ken. I had respect for you, at one point, as a Miata tuner who knew what the hell he was doing, being the go-to guy for FM back in the day and all that.
One post and that respect is out the window and unlikely to come back. Go post your narrow-minded hate elsewhere.
Originally Posted by Ken Hill is a Racist
They will think nothing of providing samples of a product exactly as specified, only to later substitute lower quality materials to save themselves money and not alert, or lie to the US customer.
As someone who has extremely high quality items manufactured in China, you know whose problem this is? The US customer's. See your engine builder's spec sheets for an example of how this happens. Round off a number here, check only one of the pistons, "close enough", "pretty much", all of these are shortcuts that, as you found out, can bite you in the ***. Not doing the labor is the fastest way to save money on labor, no matter where the work is being done.
Incoming Quality Control is a thing, as is Supplier Quality Assurance, Authorized Supplier Lists, etc. Maybe in the Joe McCarthy-fellating past you miss so much, these checks weren't formally identified, but they existed. You didn't buy from so-and-so because they sent you a bad batch one time. Your source is always going to look for ways to cut their costs without raising their prices. That's as capitalist as you can get, maybe even in your befuddled mind that's as American as you can get. If the company putting their name on the white box from China isn't checking the quality, blame them.
You want high-quality parts in a global economy? You're going to have to pay for the labor necessary to assure that quality.
Last edited by thebeerbaron; Oct 15, 2021 at 06:57 PM.
Reason: grammar
As the guy who asked for your build sheets I am leaning towards advising you to investigate more into the quality checks that both you and your builder implement. "I checked a few measurements here and there" is simply not good enough for a customized engine, especially a high performance F/I street car. There are some excellent YouTube videos by Jafromobile on the attention to detail one should have on clearances.
Finally, as a career military veteran and foreign diplomat I would strongly encourage you to set aside your xenophobia and seek to understand your fellow man.
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