Carrillo versus Maxpeeding Rods

[rgh0]

I am currently refreshing my spare Twincam race engine and I have good Carrillo rods in it that don’t need replacing. However I thought I would buy a set of the Maxpeedingrods rods ( silly name) just to compare them to the Carrillo’s I have been using in competition engine builds for the past 30 years.

The Max rods were A$539 delivered with ARP 2000 bolts ( more about the bolts later) and arrived from the local Australian warehouse in 4 days from ordering. Carrillo’s cost around A$1600 to $1800 delivered depending on the exchange rate with the USA at the time and whether you get hit with 10% GST on the import when it comes through the post and can take around a month if they are in stock or longer at times if not in stock at the usual vendors I use

I did a detailed examination of a new Carrillo rod with the OEM supplied Carrillo H6 bolts compared to the Max rod and their supplied ARP 2000 bolts with the results shown below.

1. Weight - tolerances on both rods are within +/- 1 g as delivered

Carrillo
Total assembly 519 g
Big End 399 g
Small End 120 g

Maxpeedingrods
Total assembly 564 g
Big End 400 g
Small End 164 g

The Max rods are significantly heavier with most of the extra weight on the reciprocating small end so it will load up the crank more which is important to avoid in a 8000rpm Twincam. Most of this extra weight appears to be the thicker webs of the H section which would make the rods stiffer and better suited maybe to a lower revving long stroke road engine ??

2. Overall machining finish

Overall the details of the Max rods finish is not a good as the Carrillo’s. The shot peeing is coarser and the edges are sharper and rougher. The blending of the big end into the bolt flats is not as good with a small step that is a potential stress raiser. Most of these defects would be smoothed out easily with a fine stone or file

3. Small end bushings

The Max rods have a single lubrication hole on the top of the small end and a lubrication groove on the bushing.
The Carrillo rods have 2 oil lubrication holes on the bottom of the small end and no groove

The Original specification small end bore was in two grades
A - 20.635 to 20.637 mm
B- 20.637 to 20.642 mm

The wrist pin specifications were also two grades
A - 20.627 to 20.628 mm
B - 20.628 - 20.632 mm

The Carrillo rods measure 20.640 +/- 0.003 mm and my JE piston wrist pins measured at 20.632 +/- 0.001 mm and they were a perfect finger push sliding fit.

The Max rods measured 20.618 +/- 0.003 mm and the same wrist pin was much to tight and an interference fit. These rods will need finish reaming / honing to get the size right for standard wrist pins which is the only major issue I have found with these rods. This was the dimension actually listed in the Maxpeeding literature of 20.62mm and i was not sure if this was a typo which was one of the reasons I bought a set to check. Somehow they have got the target dimension wrong by 0.02 mm compared to the Ford original specifications ?

4. Big End Bore

Both the Carrillo and Max rods big ends appear to have been well honed measuring 52.90 +/- 0.002 mm with no measurable out of roundness or taper. The ACL bearing specification is 52.896 mm to 52.908 mm so they are nicely slightly below the middle of the specification which is ideal for clamping the big end bearings in location

5. Rod bolts

The “ARP 2000” bolts supplied with the Max rods appear to be a “special” made for Maxpeeding as while the dimensions are identical to a standard ARP 2000 bolt the head stamping says " 08 maXpeedingrods ARP 2000" compared to a set of the OEM ARP bolts I have that say “68 ARP 2000”. I have no idea if this is significant or not. These bolts were the correct length at 1.6 inches under head for the rods so that the thread did not cross the cap join. Most suppliers supply 1.5 inch under head ARP bolts for steel rods so you need to check carefully which you need.

The Carrillo H6 bolts weighed 25 gm and the Maxpeedingrods ARP 2000 bolts weighed 27 g the same as OEM ARP2000 bolts

Overall the Max rods would be great for a tuned road engine rather than using old 125E rods which would probably need work to bring them back into specification which would probably cost a similar amount to the new Max rods. For a full on 8000+ rpm race engine i would probably stick with the Carrillo’s due to their lighter weight and better detailing but its hard to say if they are really worth the extra cost even in a race engine.

I will add some photos when I get a chance to upload them.

cheers
Rohan

[h20hamelan]

As usual, amazing, great, fantastic & thank You Rohan

[ill_will]

Useful write-up, thanks Rohan.

[HCA]

Hi Rohan

Thanks for making the comparison and posting! Most useful as for the price, the Maxpeed has to be good value to all but top racers,

Following your last recommendation, as you know, I have drecided to buy a set, but holding back as I am undeided on what block to use - not only do I have the choice of a 711 or 701, but now a strengthened 120e has just surfaced!

I wonder why their small-end is not to Ford spec? Would it be worth asking maybe?

Re-assuring that you come down on the side of a long stroke road engine as most suited!

Better value buying down under! Here they are 369GBP - equivalent to 650AD!!

Question: For a small increase, I have been offered an upgrade to ARP L19 bolts. Worth it, or even necessary?

[rgh0]

Hi Hal
Yes i will be following up with maXspeeding rods on why the small end bore is not the correct specification. The difference in price will be around the different VAT generally at 20% in the EU versus 10% here in Australia

I don’t think for a road engine L19 bolts are necessary and they potentially introduce other problems.

This is from the ARP web site

ARP2000®: ARP2000 is an alloy steel that can be safely heat treated to a higher level, producing a greater strength material than 8740. While 8740 and ARP2000 share similar characteristics – ARP2000 is capable of achieving a clamp load at 220,000 psi. ARP2000 is used widely in short track and drag racing as an up-grade from 8740 chrome moly in both steel and aluminum rods. Stress corrosion and hydrogen embrittlement are typically not a problem, providing care is taken during installation.

L19: This is a premium steel that is processed to deliver superior strength and fatigue properties. L19 is a very high strength material compared to 8740 and ARP2000 and is capable of delivering a clamp load at 260,000 psi. It is primarily used in short track and drag racing applications where inertia loads exceed the clamping capability of ARP2000. Like most high strength, quench and temper steels – L19 requires special care during manufacturing to avoid hydrogen embrittlement. This material is easily contaminated and subject to stress corrosion. It must be kept well-oiled and not exposed to moisture.

My reading of this is that ARP 2000 bolts need less care due their lower sensitivity to hydrogen embrittlement and all the real world experience is they work OK in 8000+ rpm engines so no need for anything better such as L19 in a Twincam race engine let alone a road engine I believe. Getting the correct stretch on the rod bolts preferably by using a stretch dial gauge is much more important. You can do it by just torquing the bolts to their specified value using the ARP lube but without checking with a stretch gauge that is less accurate.

cheers
Rohan

[rgh0]

Some photos i took while doing all the measuring.
Cheers
Rohan

Overview of the two types of rods

The finer webs on the Carrillo rods contribute to the lighter weight

Big end markings - Carrillo on left, note the smoother detail finish all over

Rod bolts markings ARP OEM supply on left, Max supply on right

Rod cap bolt seats and overall finer machining for Carrillo rods on right

Wrist pin bush Carrillo

Wrist pin bush Max

[2cams70]

There’s nothing wrong with the Maxpeedingrods rods with regards to the small end diameter. They are supposed to be reamed to size just like the OEM ones were always reamed to size. In original production the pin to small end clearance was always a selective fit and not a “one size fits all” proposition. You probably just lucked it that JE piston pins mate well with Carillo rods. Either that or the dimensional tolerance that “works ok” in practice is much greater than the original OEM +/- 0.00015”

[rgh0]

@2cams70

There’s nothing wrong with the Maxpeedingrods rods with regards to the small end diameter. They are supposed to be reamed to size just like the OEM ones were always reamed to size. In original production the pin to small end clearance was always a selective fit and not a “one size fits all” proposition. You probably just lucked it that JE piston pins mate well with Carrillo rods. Either that or the dimensional tolerance that “works ok” in practice is much greater than the original OEM +/- 0.00015”

The Ford original design, at least as listed in the Lotus manual appears, to have been a graded selective fit rather than match reaming / honing individual pair to a specified clearance

i.e.
Grade A bush and pin 0.007mm / 0.0003 in to 0.010mm / 0.0004 in clearance
Grade B bush and pin 0.005mm / 0.0002 in to 0.014mm / 0.0006 in clearance

The “normal” maximum clearance target people appear to accept when rebuilding engines is around 0.001 inch with “typical” values on new assemblies to be around half this i.e. 0.0004 to 0.0005 in for road engines and 0.0006 to 0.0008 in for competition engines

Match machining to 0.00015 in was not very practical with the machinery back in the Ford production line days and appears to not be necessary in any case.

Yes it was my original thought that the max rods require finish honing / reaming. However their literature says that they are “finish honed on Sunnen honing machine” so it appears they have been finished to an incorrect size. I have emailed the Maxpeedingrods support and I will be interested in their answer.

Maybe Max has surveyed all the current piston makers and their wrist pin dimensions and left enough material for further finishing if required. And maybe with the JE wristpins and Carrillo rods I am lucky they match or maybe they actually make them accurately to be within the original Ford tolerance specification as appears to be the case. However it looks like the original design is based on a nominal 13/16th of an inch dimension with the bushings slightly over this and the pins slightly under this to give the required clearance

Maxpeedingrods should state all their critical dimensioning assumptions in their literature if finish machining is required.

cheers
Rohan

[rgh0]

Maxpeedingrods have good customer service and responded quickly to my query on the small end busing size being incorrect. The accepted the issue that the rods were not finish honed to correct size and have paid me a credit to compensate for getting the bushings honed to the correct size. It will be interesting if they correct their literature to say finish honing is required or change the rod small end bushing bore to a more suitable finished size such as 20.640mm.

Incidentally i measured up a range of pistons pins from spare and used pistons I have i.e. JE, Arias, Venolia, and original Ford Lotus twin cam and Ford Crossflow and all would work with a 20.640 mm bore small end that comes with the Carrillo rods.

cheers
Rohan

[2cams70]

Just checking the Ford workshop manual as memory can fail me these days:

Small end bush in connecting rod is graded:
Grade A: 20.637 to 20.640mm
Grade B: 20.640 to 20.643mm

So anything in the range 20.637 to 20.643mm is within OEM spec.

Piston pin to small end clearance: 0.076 to 0.127mm.

Interestingly the clearance tolerances on the standard pushrod engine are much tighter than on the twin cam. The ordinary cross flow engine has 4 grades of small end diameter compared to 2 with the twin cam and piston pin to small end clearance is an order of magnitude tighter at 0.003 to 0.008mm (not inches!) selective.

Also of note is that the material spec. of the 125E connecting rods is stated as being EN15B steel - so they are made of sterner stuff than a standard cross flow rod

[HCA]

Well, all I can say is that Maxpeeding Rods, despite their unflattering name, are certainly joined up internally!

This morning I had a note that my rods are being despatched today. Then followed up by another note that a credit of 55€ is on my paypal account, saying that their machining of the small end is below specification and that I should have them professionally honed to fit the pistons…they estimate the cost to be 55€!

Well done Rohan - it seems that they have taken your comments on board and applied it to all rods that are in stock…impressive.

Book price was 435€, but then I had a 30€ black friday discount, so now nett price therefore is 350€ !

[RichardHawkins]

Rohan,

I am amazed at the detail you have gone to, what are you using to measure to such precision?

Richard Hawkins

[rgh0]

I use Mitutoyo meausuring instruments and have collected a fair range over the years. A few photos below of what I use.

The 0 - 25mm micrometer reads to 0.001 mm. It and the 200mm dial caliper that reads to 0.01 mm are the things I use most for checking dimensions of general parts. i prefer older style mechanical measuring instruments rather than electronic read outs as their batteries never go flat

Larger 0 - 150mm micrometer with selectable rods and calibration blocks, graduated to 0.01mm but can interpolate to about 0.003 mm. Used for larger precise measurements such as main and big end journals and for setting up the dial bore gauge with its 50mm to 150mm range for big end and cylinder bore measurments.

A range of telescoping and ball end bore gauges used mainly for smaller things such as valve guides that are less than 50mm diameter where the dial bore guage does not fit.

Depth micrometer, does not see a lot of use but handy to have. Most depth measurements do not need to be very precise and the rod end of the dial caliper is accurate enough

Magnetic stand and dial guage mainly used for verifying TDC and measuring valve spring load versus deflection

Miscellaneous spring calipers for getting into difficult to measure locations and 150mm and 600mm metal steel rulers / straight edges

This covers pretty well all the mesaurement checking needed when stripping and rebuilding a Twincam. I keep looking for excuses to buy more

cheers
Rohan

[pharriso]

When I grow up I want to be Rohan

[rgh0]

@pharriso

When I grow up I want to be Rohan

Forgot a couple of other essential measuring devices when building an engine

A dial stretch gauge for measuring rod bolt stretch. Essential for getting them accurately tensioned as torque alone is not accurate enough for Rod bolts especially in racing engines

A pippette for measuring combustion chamber volumes

If you dig deeper into my workshop shelving you will also a fair collection of other diagnosis devices e.g. compression tester, battery tester and a few multimeters and clamp on current meter, leak down tester, radiator system pressure tester, modern VW VCDS diagnosis cable, wide band O2 meter for A/F ratio testing, weigh scale to 1 gm ( need a new one to at least 0.1 gm for Christmas )

cheers
Rohan

[Craven]

All transferred to a temperature controlled room 24hours before measurements made I’m sure.

[rgh0]

Yes the instruments live in the same space as the parts which in a well insulated shed at the rear of my garage so they are at the same temperature as whats being measured. In any case temperature is stable around 20C for most of the year due to the mild Melbourne climate

In the end the results are accurate enough for engine building, if not for some metrologists

cheers
Rohan

[RichardHawkins]

Rohan,

I am still amazed. My 0 to 25mm micrometer is also Mitutoyo but with digital display, the battery is usually flat! I cannot get a repeatable measurement with this tool as the last number is different at every attempt, it seems that just the temperature of my hands is enough to alter the result. I do have a heavy engineering background, mining and mineral processing, perhaps I am a bit rough and am the limiting factor.

Richard Hawkins

[Craven]

I always have to smile when some people state very close measurement figures, be it mechanical or electrical, and the delightful way accuracy and precision are muddled up, some clearly think they are the same.

[snowyelan]

There is a little plastic pad in the middle of the micrometers ‘C’ which is where you hold it with your fingers. It is there specifically for insulating the mic from body heat.

When measuring I prefer to compare to a gauge block buildup, set to mimic the required dimension. Dirt, wear, and manufacturing tolerances all come into play and I don’t like assuming the tool is accurate at any given point within its range.