The Stovebolt Site Forums The Shop Area Engine Shop Piston pin locking bolt 261 engine

Fellows,

I`m working on a friend`s 261(brazilian built engine - 1964), and it uses a connecting rod equiped with the locking bolt to hold the piston pin. The question is: what`s the required torque to tight this bolt? Cannot find this info nowhere in the shop manuals I have here. I`ll be assembling his engine in a coupe of days and I`m quite worried about it.

Thanks in advance.

I torque the ones on my engines to 25-30 ft lbs, use a quality lock washer and Loctite.My manuals say tighten the bolt securely??? I'm sure you know this ,but remember to insert a long drift into the pin then put the drift into vise when you torque down the bolt.This way the connecting rod won't be twisted sideways as you tighten.

I was told 25-35 too and I did mine at 30 ft lbs. Most rebuilders are careful to point out that you should use new lockwashers as they can get brittle.

Thank You Fellows,

I read several manuals from Chevrolet and all of them said tp tightem them securely, tried to find securely in the torque wrench with no success, so used 40 pounds. Will redo it using loctite. The engine is still apart and it's time to do it right. By the way, if You could choose between the regular rod with the press fit and the one with the bolt, what would be your choice?
Have assembled earlier jeep engines, never had any problem, and I can get a set of used/resized rods for the 261, but the normal, interference, boltless type. I'm into getting the newer set, what to do?? Opinions, please! It'll be a Hot Rod engine, will go into a brazilian built sports car os the 60, looks like an Avanti, 3 single barrel carburetors, 4 speed, 2750 lbs car. Has zero deck height with flattop pistons, milled the head 060", 270' degress duration cam (local cam grinder, grind based on an early Isky profile) and headders. Suggestions are obviously wellcome!

Get a solid stock manifold and have it split by Kansas Kustoms Know where any manifolds are? Look on ebay

There are no replacement 261 rods of any kind available in the USA, maybe the bolt-less variety are a Brazil-only item.

Any serious Chevy racers of years gone by used GMC 228 connecting rods as they are much beefier and eliminate a point of failure on the pin bolts. Same journal sizes (I think - have to look it up) but the pin height is different, so custom pistons are required.

An upcoming Inliners article details how to use 292 rods and Cadillac V8 pistons, along with offset grinding the crankshaft, to get up to 301 cubes out of a 261. Cheap and readily available parts, as the 292 uses the same rod bearings as the small block V8. This might be worth considering.

I'd use whatever is lighter, which I suspect is the bolt-less rod. Pistons accelerate and de-celerate like mad; even a few grams of weight is major extra stress on the rods and rod bearings.

Yeah, I know, you're not building a race motor. ;-) But even in street driving, it's better to reduce the stress when you can.

Cheers!
George

'53 3600, 235, etc....

Luke,

The engine is out of a Brazilian built Uirapuru, a sports car using a truck engine, it was originally equipped with tube headders and 3 SU carbs. They will be kept there. So no need to worry about it! Anyway, quite cool suggestion.

Sixpack,

Brazil is the sotebolters paradise. 261 were available brand new up to 1976 (and as incredible as it may sound, the 292 **** Y block also made it to 1976 - we only lost to canada, were the flathead V8 went to 1980) in many commercial vehicles, then were supersseded by the 250 and 292. Long time ago we discussed the modifications using 292 pistons/rods and stroking, and as I recall, Chevyman remembered quite well that the narrower 292 rod would not provide enough side trust for the rod, and that would it'd be no good. So by that time I quit the idea of stroking in, although it is possible just to bore it all out to 3 7/8 using just the 292 pistons.
By the way, all the machining is over now, decked it to get a zero deck situation. The only doubt by now are the rods. I'll go to a big engine shop tomorrow and will try to spot a set of boltless rods for the 261, they were available here, virtualy identical to the normal rod, just no bolt to tight. Assemble just heating it as well as any other press fit rod.
Just for your information, down here we have even a 250 L6 with EFI, multi point sequencial fuel injection. Go figure! And try talking here about chevrolet V8, most guys do not even thing they do exist! They have never being brought here by Chevy or GMC.

George Grenley

Guess the boltless is lighter. If I find it, will pick the whole set.

Fellows,

Life is beautiful. Went to the junkyard, found a decent 261, took all the rods, forging 7326090, the very same forging as the one in the rod with the locking bolt, only not machined to have the bolt, and of course, not cut, machined to the right interference value, the pin has to be pressed in or the rod heated to allow the pin in.
The best part, the rods were all ok, no need to rebuild, measures all ok, no twist or bent. paid 33 dollars for the set.

Alexandre,

Just curious, what size and type of piston rings are used on the Brazilian 261's? Do the later engines use the original ring pack?

Yes Alexandre--

I can believe that Brazil is stovebolt heaven. Here in Texas, virtually all the Junkyards pull the old engines, pile them up and when they get enuff--truck to Mexico or ship to S. America. gotta be a whole lotta stovebolts down there. Sounds like you could open a cottage business shipping 261 rods back.

Hey you bloters have me scared now, by that I mean, never did I apply any loctite on my locking bolts to my rods. Has anybody besides myself not applied loctite? The bolts were torqued at 35 ft. lbs with new lock washers and grade 5 bolts. Now this engine is a 235' 6 cyl. Let me know before it is to late THANKS..

sixpack,

The piston is the very same stuff of the sixties, they can be obtained brand new from Enginetech (metal leve) as # P572. Rings the same 3/32 and 3/16. All production years here used the same pistons and rings. After assembly you'll find a piston that remais .050" below deck.
As a curious fact, we use alcohol (ethanol) as a fuel, and for sometime this company Metal leve used to sell some conversion pistons, they looked like any hogh performance pistons of the 50's, had a tall dome that went thru the head to give a good comp ratio.

bznhafdzn,

The L6 chevy engines were always quite popular here, offered a good relation between power and fuel consuption, and were produced here for a long time.
As for the rods, the fact is simple: probably one day someone realized that was easier to just bore the rod head to the pin plus interference dimension than to have it cut and drilled to the locking bolt. It has the forhging number 7326090. And the boss to be drilled to the bolt is still there, no one cared to remove it. As
And as for sending rods or any other stuff from here back to the U.S. is quite simple also, if anyone eventually needs anything, just mail me and I'll be able to get and ship it to the good old U.S.A.

ol'55
As long as You have torqued them all down to this value, no need to worry about it. They just were not assembled with loctite when new and did not failed for the lack of it. It should have been good to use it when You assembled, but I see no point in taking it apart just for it.

Say there Bolter #1948 I sure appreciate the positive reply on application of the loctite. I realize now I probably should have used the loctite but I never have in 30 years so hopefully I'll be allright.Ok any of you other bolters running around town without loctite on your locking rod bolts give us a reply.. THANKS OL'55 :confused:

Ol'55,

Took a while to see if we could get another answer/opnion, but as long as no one showed up, here are some more 0.02 about it:
I've been assembling engines as for living for a long long time(nearly 20 years). Since I work basically with american made engines, I traveled sometimes to the U.S. to learn with some cool fellows that do not mind sharing their knowledge, and also got a ton of books and manuals to learn how to make my job right the first time.
One thing to be seriously considered is the fact that what keeps the nut/bolt from getting loose and falling apart is the fact that the tightened element suffers a programed elastic deformation, and within the proper limits this elastic deformation holds things quite well. And of course the fact that the required torque for the nuts/bolts consider the presence of oil and the oil normally has a constant drag coeficient, loctite has another specs. get for example a set of ARP bolts, they do furnish You the required torque using oil and another for themoly lube they do furnish, and they are completely diff.
Sometime ago there was a very good article on Mopar action covering this subject, and of course they stated the best way to measure the right amout of torque to a bolt was the stretching method. The deal is that it is not possibleto all bolts. The one You asked, for example, is not possible to be measured.
Now my personal opnion: I do use loctite in engine assembling except for one aplication: I understand that the 3 small bolts that holds the cam in all chevy V8 engines and in big mopars. They are quite small, 5/16 NC, and require 25 foot/pound of torque. The fact that all these bolts rupture at near 30 foot/pound leaves li'l margin for error. So I see clever to use the red loctite (271) and torque them to 25 pouds. Except for this case,I do not use it. Although for some non-critical aplications such as holding carb studs to aluminum manifolds, transmission locking bolts in a complementary way to the locking wires and so on. This is based on the info and comments I got from others that do know muchmore than I do and the fact that my personal experience and lack of failures for this long period of work leads me to think I'm in the right way.

Best Regards,