Carrillo WMC bolts

[The Turk]

Well, I didn't do my homework and I bought Carrillo rods with the SPS-WMC6 bolts rather than the SPS –CARR bolts.

Carrillo tells me these are a huge improvement over stock 3.2 bolts, in fact he said that the main practical difference was that the WMC should be replaced after being torqued down 10 or so times and the CARR could be reused many times over.

I’m just starting the final assembly on the motor, I assembled the crank/rods last weekend, all the rod bearings clearances came in at .0019 to .0020 .

Carrillo recommends .005-.007 stretch with the torque not to exceed 45 foot lbs., I measured the stretch of each bolt, all took maximum torque (45 foot lbs.) to reach stretch of .0044 (one bolt) to .0057, most came in at .0049 - .0051.

I’m a little worried, did I make a big mistake using the WMC ?

Here’s the basic motor:
3.5 Mahle 7.1:1
Rods, pistons & pins balanced within ˝ gram
Crank was magged, micro polished, checked to be straight and balanced
GT2 Evo cams
930 oil pump
930 piston squirters.
Complete Protomotive twin turbo setup

[MBruns]

Those bolts are just fine, we use those in many race builds and have not had any issue's, we use the SPS carr bolts as well, Just follow procedure and rest easy
Mike Bruns JBRacing.com

[The Turk]

That's great news, what RPM do you think they'll be good to with the Mahle 3.5 pistons ?

Short bursts to 7000 ? 7500 ?

[Jeff Alton]

Intersesting, In my limited experience measuring stretch I too have found the aftermarket bolts take more torque than one would expect to reach the desired stretch.

Cheers

[CBRacerX]

Originally posted by catca
Intersesting, In my limited experience measuring stretch I too have found the aftermarket bolts take more torque than one would expect to reach the desired stretch.

Cheers

I have used a stretch guage that does not permit checking the torque while measuring the stretch (ARP guage). The instructions I have read from ARP seem to imply you can use torque or stretch (much preferred) but not both to get the bolts properly tightened.

[MBruns]

We have 911 2.0 race engines with those 3/8" SPS-WMC6 bolts that operate all day 6500-8500 and work fine, I race a 3.8 911 engine that uses the same bolt in the 4000-7800 range that produces over 400 hp with carbs, on the dyno we turn it to 8000. Dont worry about the bolts, worry more about the oil clearences and proper stretch of the bolts

Mike Bruns JBRacing.com

[The Turk]

CBRracerX,

I returned an ARP stretch gauge after talking with the guys at Carrillo and used a standard micrometer, I followed Carrillo’s instructions but took them a few steps further.

Carrillo say’s to “Simply fixture one rod leaving the cap portion free from clamping load.
Measure both bolt lengths loose, then progressively tighten the bolt until the measured increase correlates with the figures below. Use the indicated torque reading to tighten all the connecting rods in final assembly”

The “figures below” are “.005 to .007, torque not to exceed 45 foot pounds”

So here’s what I did, the Carrillo’s I have were brand new and came torqued up, I took a rod and clamped it into a vise using wooden jaws (not going too tight), I measured both bolts and wrote down the length’s, I then progressively loosened the bolts until they were completely free of load and measured the length’s again, the two bolts were stretched from Carrillo .0049 & .0046, not quite the .005 to .007 they recommend.

I then progressively torqued the bolts, 20 lbs., 30 lbs., 38lbs and 43 lbs. measuring at each range, at 43 lbs. I was just under the minimum recommended stretch of .005. I repeated this procedure on 2 more rods with similar results.

So knowing that the stretch on the bolts when they arrived from Carrillo was slightly under the recommended minimum of .005, and at 43lbs I was just under .005 on 3 rods I decided I would assembly the crank using the recommended maximum 45 foot lbs. measuring along the way.

Here’s what I came up with:
Rod 1 – bolt 1 .0049 / bolt 2 .0052
Rod 4 – bolt 1 .0052 / bolt 2 .0045
Rod 2 – bolt 1 .0049 / bolt 2 .0057
Rod 5 – bolt 1 .0051 / bolt 2 .0048
Rod 3 – bolt 1 .0047 / bolt 2 .0046
Rod 6 – bolt 1 .0044 / bolt 2 .0048



Mbruns,
I appreciate the info on your 3.8, I’ll sleep a little better knowing a big motor with the same bolts/rods gets spun up to 7800 on a regular basis.

Here’s what I did, let me know what you think.

I mic'd all the journals and each bearing half and used a bore gauge on the rods, I weighed each piston, pin and rod, since everything was new I mixed and matched until all the assemblies were within a 1/2 gram and all the journal clearance were either .0019 or .002.

I was able to place the two heaviest assemblies on 3&6, next heaviest on 2&4 and the two lightest on 1&3.

I used plastigauge on the mains (.003) and intermediate (.002+)

The 3.5 I’m building is replacing a pumped 2.7 that loves to wind to 7200 and has done so virtually every day for the last 16 years.

Not counting cleaning, all the measuring and the assembly of the crank & rods took about 10 hours, I really want this new motor to be able to spin up to 7000+ reliably.

[CBRacerX]

Gary,

Thanks for the writeup, interesting approach and no "special" tools required - I like that

The ARP dial indicator is a time saver, but certainly not required as you showed.

Cheers,

Chris

[The Turk]

Hi Chris,

I know I've found lots of useful info on this board over the years and I like as much detail as possible, hopefully this can help someone else out.

I fully intended to use the standard stretch gauge, I had already bought one and ended up returning it unused.

The guys at Carrillo convinced me to use the method below, you'll see pictures similar to mine on their website.

http://www.carrilloind.com/install.html

I believe if I had of used the ARP style gauge I probably would have taken the torque past Carrillo's recommended maximum 45 foot lbs., since they are recommending .005 to .007 stretch I would have shot for .006. which would have been about 55-60 foot lbs. (guesstimate)

[MBruns]

That rod brg. clear. is a little tight, if the housing bore on your new rods is on the small side of the limits (which they normaly are) and the crank journal is strong std. you will have those kind of clear., we shoot for .0028-.003 in. on the performance engines and have great luck with the brgs.
Mike Bruns

[CBRacerX]

Originally posted by MBruns
That rod brg. clear. is a little tight, if the housing bore on your new rods is on the small side of the limits (which they normaly are) and the crank journal is strong std. you will have those kind of clear., we shoot for .0028-.003 in. on the performance engines and have great luck with the brgs.
Mike Bruns

What do you do to increase the clearance?

[The Turk]

Mike,

What are the disadvantages of being a little tight ?

[MBruns]

With the OEM brgs. its a little tougher, we start with opening up the housing bore to the upper size limit, message the brgs. on both sides.and keep checking the clear. with a dial bore guage.
the problem with them being tight is bearing damage and heat and ultimate failure. when we go to the 2.0 in. chev. journals on the 911 the bearing selection is huge and you can get bear. that are different sizes and can select uppers and lower brgs. to get what you want plus if you want to coat the brgs. start with the largest set and they will tighten up about .001
Mike Bruns

[mikedsilva]

Originally Posted by The Turk

Well, I didn't do my homework and I bought Carrillo rods with the SPS-WMC6 bolts rather than the SPS –CARR bolts.

Carrillo tells me these are a huge improvement over stock 3.2 bolts, in fact he said that the main practical difference was that the WMC should be replaced after being torqued down 10 or so times and the CARR could be reused many times over.

I’m just starting the final assembly on the motor, I assembled the crank/rods last weekend, all the rod bearings clearances came in at .0019 to .0020 .

Carrillo recommends .005-.007 stretch with the torque not to exceed 45 foot lbs., I measured the stretch of each bolt, all took maximum torque (45 foot lbs.) to reach stretch of .0044 (one bolt) to .0057, most came in at .0049 - .0051.

I’m a little worried, did I make a big mistake using the WMC ?

Thought I would add to this thread as it was the closest to what I was looking for, and no need to start a fresh one. Yes, I know it is 14 years old!

My first use of Carrillo rods and bolts confused me a little. Looking at the instruction card, it says the stretch range of my 3/8-24 WMC H6 bolts to be 0.0050 to 0.0065 with a Torque Not To Exceed of 40lbft.

Well at 40lbft I only got 0.0045 stretch using an arp stretch gauge.

Increasing torque, at 48lbft I am only just getting to 0.005 thou stretch.

So I called Carrillo... spoke to Richard..
He said on those bolts most people are up around 50 lb ft....and that the instructions are being reprinted and to pretty much ignore the torque setting.

When I mentioned I am at 5 thou stretch, he said to increase the torque to get in the upper half of the stretch range as that is what is giving the clamping force and is most critical..