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Discussion Starter · #1 · (Edited)
I just received my new rods 😋

These are made by Carrillo, a big name in motorsport. I took their standard (3/8 WMC H6) bolts, which are good to 8’000rpm on our engines I was told. They also offer higher grade bolts for higher speed engines, but the cost is not justified on a (relatively) slow-revving turbo engine.

The rods are shot-peened, which enhances their crack resistance and gives them a satin appearance. The brand is laser etched in a very sharp and thin font.

They have a machined tang to keep the bearing from rotating (the OEM rods don’t have that cut and only accept plain bearings) and I’m going to use King’s CR4604XP bearings with them.

Rods are not rated by horsepower, more by the cylinder pressure they can withstand and the RPM’s they can support (which is also a bolt affair), but this depends on the bore/stroke, and piston assembly weight and acceleration. If you really wanted a number it would look like 275hp per rod.

Mine came with outdated instructions, the latest version for torque steps and bolts stretch is available online.

The Carrillo product number is SCR10227, aka F_BEB23_0HS_5878_B6H. They come with special bolt lube, neatly packed in individual boxes

For DIYers: You need a 7/16-inch 12-point socket to tighten the bolts, and a good torque wrench and angular gauge, and/or a bolt stretch gauge, which is the preferred way. The best is to land in the upper half of the stretch range (but never exceed it!) to ensure proper tension.

I weighted them on a lab scale. The average weight with the bolts of my particular set is 562.75g, min. 562.34g, max. 563.34g so the whole set is within one gram.

I’ll update this with the nominal weight (without bolts) when I get a chance.

The Ford rod’s average for the set that came with my original engine is 593.46g, min. 590.86g, max. 596.06g, so the set spans 5.2 grams.

The Carrillo rods are thus about 5% lighter than OE (31g per rod) while being much stronger and RPM-capable. The weight tolerance is much tighter than OEM, actually three of them are within 0.5g of each other, with one outlier, but I’ll not try to chase the fractional grams and ruin the surface finish. Edit: I eventually did and matched the weights of all four to less than the 0.01g I can measure.

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nice. I would feel much more confident tuning over 7k rpm / 475 hp with these.

so you're rebuilding your motor I take it.
did something happen?
or you just feel like it?
 

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Discussion Starter · #3 · (Edited)
Nothing sinister happened but I have to do a clutch + flywheel now, the clutch slips down to 3rd gear, and possibly a head gasket because I have an exhaust gas leak to the coolant system.

I decided to rebuild the other engine (the one that originally came with the car) that was laying down in pieces, and thus I’m adding a few missing bits, grinding the head (a bit more aggressively this time) etc.

If I have to remove the head and the gearbox I figured it would be easier to just pull the engine out, and one thing leading to another I’ll do a swap, then I’ll rebuild this one later.

Hopefully I’ll just recondition it (remove the carbon etc) put new rod and crank bearings, new seals all around, new head gasket, and basta, but I’ll need a new machine shop that can do the required surface finish on the head, as I suspect the last job wasn’t entirely appropriate for MLS gaskets although the shop assured me it was: the surfacing left marks of maybe 1-2 100th of a millimeter but the roughness should not exceed 50 Ra ≈ 1.2 microns.

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Happy day for you! Those rods look boss, great choice and thanks so much for doing the analysis on them. I will choose these rods when the time comes. Any crank work?

Speaking of the time coming, I see you mentioning possible head gasket due to exhaust gasses making into the cooling system. I have questions for you about this but don't want to detail this thread, i'll bump your other one.

I will ask, which head gasket are you going with? What's the spec on the machining required, why?
 

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Discussion Starter · #7 · (Edited)
Happy day for you! Those rods look boss, great choice and thanks so much for doing the analysis on them. I will choose these rods when the time comes. Any crank work?

Speaking of the time coming, I see you mentioning possible head gasket due to exhaust gasses making into the cooling system. I have questions for you about this but don't want to detail this thread, i'll bump your other one.

I will ask, which head gasket are you going with? What's the spec on the machining required, why?

Happy day for you! Those rods look boss, great choice and thanks so much for doing the analysis on them. I will choose these rods when the time comes. Any crank work?

Speaking of the time coming, I see you mentioning possible head gasket due to exhaust gasses making into the cooling system. I have questions for you about this but don't want to detail this thread, i'll bump your other one.

I will ask, which head gasket are you going with? What's the spec on the machining required, why?
The crankshaft is from Callies, part number QH47BTO-F2. It’s 4.5kg/9lb lighter as they machine out the entire balance shaft drive gear, plus other treatments, balancing, and keying. I got mine from Mountune USA as they also supply a keyed crankshaft pulley.

I bought a 3-Layer MLS gasket from Mountune this time, part number 2536-MLS-AA but I’d have gone for a 4-Layer Cometic if they had some in stock. I know Cometic for years and their stuff is 100%. The surface spec varies depending on the gasket manufacturer, I found figures between Ra 10 and Ra 80. The number is the average peak-to-valley of the surface in millionth of a inch.

Mountune says their gasket has a 0.27 micron coating so I guess the surface roughness must be in the same order, which on 2nd thought should be between Ra 10 and Ra 20, which is not far from mirror finish around 600-800 grit (I’m still learning that stuff.)

The surface requirements are gasket-specific but as a rule of thumb if you can feel anything on the surface with your nail, it’s probably too rough.

Mine took 18 months and more than 30’000km to start leaking and I charge all the stock turbo can charge, so it’s a very slow process. Expensive lesson learned - I used a well know shop but maybe not modern enough, this time I’m going to specify the surface finish quality in writing.

Head studs are going to be ARP CA625+ that are available from SP63. I’m sure it’s overkill but I’m not taking any chances.
 

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Discussion Starter · #8 · (Edited)
Is that excess pressure in your expansion tank what caused your tank to leak, or do you think it was totally unrelated?
Yes I think so. I eventually fixed it with silicon sealant and after that the coolant level was still going going down, almost imperceptibly but surely.

After 3 weeks of doubts I bought a chemical test kit from Amazon: Block Tester BT-500 Combustion Leak Test Kit https://www.amazon.com/dp/B06VVBSFTF/ref=cm_sw_r_cp_api_i_BAK074HGGSEHQQJ1QAQA?_encoding=UTF8&psc=1 and sure enough it turned yellow-green so exhaust gas there was.

This test kit is great because there was no alarming signs at all, no excessive white smoke on startup, no foam, no bubbles, no coolant smell (after I fixed the pipe), nothing but a very minor water consumption at first.
 

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Discussion Starter · #9 · (Edited)
OK I did it: I matched the rods weight by grinding the sides of the big ends and caps, using wet sandpaper on a flat glass (my kitchen stove) P220, then 400, 600, 1200, 3000 and a bit of polishing. They are within 10mg of each other’s now, I cannot measure the difference with my scale 🤓

I did not buy a dedicated rig ($270 😳) to measure both ends independently, I tried using two scales and I never got repeatable results, like the same rod weighted twice within seconds giving different numbers.

The small ends are identical in every dimension I could measure or see, I figured the differences had to be on the big end side.

I actually can see minute differences in the bolts lengths: either the bolts are slightly uneven, or the rod caps have minute differences that were evened out when honed to the final spec. In any case I had 0.17g, 0.41g, and 1.0g to remove on rod #1, if you look closely you’ll see.

I ended up grinding out a little more as I also polished the lightest one. It took a long time but I like the result. The final weight of each rod is 562.02g with bolts.
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