Inliners International Forums General Discussion Engines 261 lube question

I fired up my freshly OH'd 261 for the first time yesterday. I pre-lubed with the drill several times to get oil to the top end previous to installing my mini HEI being careful to watch the distributor fall into the oil pump drive while rocking over the engine by hand. I'm using an Oberg filter in place of the canister type. On pre lube, I showed good oil pressure. Primed it in the carb and it fired up and run good until that gas was gone. Done that twice more until I got fuel to the carb via the pump. The next time I tried it turned over real slow. I put the screwdriver to the starter ring gear and it turns with much resistance as in seized bearing. Question: can you get oil to the top end without going through the bottom end first? I have a flow diagram for a 235 but not for the 261 with the full flow filter. This one has me stumped

Dear PB;

Yes; you can get oil to the rocker arm assembly W/O going (completly) through the "lower end".

Which 261" block do you have?? Is oil going through your filter?? Will it turn with the starter now?? Where is your oil pressure guage connected??

A 235 oil flow chart is similar, but not the same as; the 235 doesn't have a 'full flow' filter option.

Good luck.

John,
Yes, oil is going through the filter. It is a late '58 block. My pressure gauge is in the rear fitting going to the filter. With the spark plugs removed, the starter has a hard time rolling it over. Something is definatly wrong inside. I've already started pulling it out. I pulled the starter off first and tried rolling it over by hand thinking maybe the starter was binding, but it still it tight.

Just finished pulling the 261 apart after a total of about 10 seconds of actual running time. At first glance it appears as if I didn't have the dist. pulled down tight enough to stay engaged in the oil pump. I left it a bit loose so I could adjust the timing. The O-ring under the flange held it up enough to keep it out of the drive. After much measuring with and without the ring, when NOT engaged in the pump there is only .128" gap between the flange on the dist. and the block. There is a lot of vertical play in the dist. shaft.
My assessment of the damage done after 10 seconds of no oil is: the rods and mains look OK, but the piston pins on the two rod caps I have pulled (2 and 5) are seized tight.

That's good news.

Put that distributor on the shelf & use a stock one, till this problem is resolved. You'll know when it's in 'all the way' etc.

Put some STP on the rod/main bearings for 'insurance'.

Good luck.

John,
In all my years of engine building, I've never seen the piston pins seize. I'll know more today after I pull the head and pistons out. I'm still not 100% sure the pump wasn't turning, but appears so at first glance. The pressure hadn't registered on the gauge yet in the cab, during the two short times of running because of the very small orfice in my pressure fitting at the block.(a trick I learned from my crop duster friend who is always asking "what if" In his case, a failed line would mean a fire, not good news in the air)
Thanks for your reply
Randy

i had the same problem with the mini hei. but i caught mine before i had problems. the problem is when there making them. there not making the shaft long enought !!! in mine i took the o-ring of and used a thin paper gasket and that seemed to take care of the problem.
when i reinstalled my mini hei i used a screw driver to trun the pump to aline with the shaft on the hei to get it to fall into place right. when the motor truns over the cam will pull the grear on the disturbter shaft down. when you restall the disturbter us a small pieace of clay on the bottom of the gear to make shure the gear is bottoming out in the oil pump.
one more area to look at is the oil pump ! was the oil pump installed right. was the oil pump locked in with bolt ?

Dear Randy;

Next time spin the pump till it reads on the guage and watch while running too.

I've never seen/heard of the pins siezing either, especially in 10 sec etc. Something else went wrong there.

The Dist. shaft should go into the pump a 1/2 inch. Check the HEI against a stock one to be sure they are exactly the same lenght too.

Also; How tight is the bolt that centers the pump??

John caught the question I was going to ask. When I use a stock oil pump I do not tighten the centering bolt tight. I let the oil pump "float" a small amount. This is on GMC's.

This can also make the HEI not drop in low enough if you are not doing something with the stock flange. I have machined them of and made my own clamp which allowed me to lower the HEI into the pump. On the one which have the pined "extention" I have welded additional material on the the length and heat treated it. None of those have ever failed...Good Luck

Thanks guys for all the input! After spending the day tearing down and scrutinizing every last detail, I've come to the conclusion that the pump was turning and even if by chance it wasn't for the ten seconds this engine ran, it didn't cause the piston pin failure. Number 2 and number 5 pins were both galled terribly in the pin boss one of them so bad I broke the piston pressing the pin out. Also the bottom of the skirt on that one was galled due the the terrific side load due to the seized pin. All the others looked fine. The pins are not lubed by the pump anyway so it couldn't have caused the problem. My only explanation is that either I didn't lube the pins enough, or they were not fitted right. Anyway new pistons are enroute and I'm further educated in the school of hard knocks.

Randy

Dear PB;

Those pins should slide right through at room temp. They 'press' into the rod. Put a little STP on them but keep it off the rings/cylinders.

"bench check" that pump and just put the 'centering' bolt (pointed end) in till it touches & back 1/4 turn & lock the nut.

The rest you know.

Good luck.

Sounds like the piston pins were fitted into cold pistons,a tight fit,and the piston pin hole became broached,siezing the pin before the start up.Many builders warm the pistons before fitting them to the rods so the pin fits easily.Of course,the piston pin bores may have been machined improperly in the first place,something to check out.

Here's the interesting thing guys, I slid all those pins in the pistons when I assembled the rods to them. All seemed good at that point. I'm beginning to suspect it was my own fault. I ususally wipe or blow everything off with laquer thinner or avgas to get it good and clean before starting on anything, possibly I didn't get it lubed up good before I slid them into the bores?

Randy

PB;

That would do it (dry) pins.

Tony is right too, if your working in a "really cold" shop. Usually 70F +/- is okay but they MUST be lubed.

There many types of 'assembly' lube for this. The main thing is that you use just SAE 30 oil on the pistons/rings for them to 'seat' properly.

I used STP (bearings etc) when I was doing it as; it insured lubrication till ran a bit. I would use cleaning solvent/kerosine as they have oil in them for cleaning. Laquer thinner/gas are dangerous & clean to good (as demonstrated).

EVERY Mechanic has learned (something) the "hard way" & why they call it; "the school of hard knocks".

Doing it twice has another name. :p

I'm not that familiar with a 261/235 on their pin fits. I use Prolong assembly lube on the pins. The stock GMC rod has a lubrication oil thru the rod to lubricate the pin on the rod. Most after market rods do not do this and pins are only lubed from the oil ring land which has a passage. (Arias)

Many machine shops are not as familiar with what is known as a "palm fit" which is described in the GMC ovarhaul books for the rod to pin clearance. When using smaller pins I direct them to make the clearance in the rod bushings so you can push the pin thru with your palm. I have never lost a rod at the pin in over 30 years of LSR racing.

The after market rods also get oil from the "splash" of the oil from the side clearance of the rod. Scrapers and side catching pans take some of this away.

This probably doesn't mean much for a stock style engine but pin clearance and lubrication pay a big part in longevity and not looking at your rods thru a hole in the block...Good Luck

Randy,

How were the rods held when the torque was applied to the pin clamp bolt on the small end of the rod? I have heard that the rod can be bent or twisted if the rod is just clamped in a vise. I slip a drift of the proper diameter through the pin and clamp the drift in a vise, and then apply the torque to the bolt. This puts a minimal load in the rod. I recall that I read about this method in a Hot Rod magazine back in the early fifties. The shop manual is a little vague on how to do it correctly. Were the rods checked for alignment as described in the shop manual?

However, if two of the pins were frozen after only ten seconds of running, it is not obvious that alignment was a problem. If the piston was warm when the pin was installed and assembled, and the engine was cold when the startup was attempted, the piston could have contracted enough to sieze the pin, especially if there was insuffient lubrication during assembly. A temperature drop of 50F will cause the pin hole diameter in the aluminum piston to decrease about 0.0006", while the diameter of the steel pin will only decrease by 0.0003". this would produce interference if the "warm" assembly clearence was less 0.0003". The shop manual calls for a "slip fit", which is looser than a palm fit.

Shop Manual

I will be starting up a recently rebuilt 261 in a few weeks, so this is of extreme interest.

Hoyt, You touched on an interesting subject, one I asked myself while trying to figure this whole episode out: the torsional force you put on the rod while tightening the pin clamp bolt. I'm with you on this, I definitely think you should run something through the pin and hold it while torqueing the bolt.
The temperature variation you all brought up would not apply in this case as everything in my shop has been a pretty constant temp during the whole assembly period and for start up, probably around 60F.

Thanks guys for all the valuable input. I really appreciate this website cause most of the guys are just here to offer some down to earth help and not out to prove a point. Keep up the good work. I never thought I'd see the day I enjoyed working on old six-bangers but it has been fun. All my friends think I've gone off the deep end for not building the VEE things like 99% of the rest of the world does. To each his own! Sorry for the long post.

Randy

Even tho I spoke of GMC rods, it was a standard hop up to use GMC rods in 235's and 61's. Not knowing the length of a Chev rod the use of a GMC is a natural especially if you are having pistons made. You no longer need to worry about the upper end bolt which has to be a weak point...Good Luck

HI guys,
Well after the dry piston pin fiasco, I"m ready to pre lube the 261 again prior to start up. Question: with the oil filter off, turning the pump slowly, I get oil out of both holes. I know the front one comes right off the oil pump but with no filter, why would I get oil out of the back one. If both are pressurized while running, how can oil pass through the filter?
Randy

Dear Randy;

One is comming from the pump & the other may be via the crank. The larger volume/pressure overwehlms that when running.

With the filter installed, spin the pump till there's a 30# reading on your guage. Then (distributor in) spin the engine (plugs out) till there's a reading to be sure etc.

Filling the filter first, helps too.

Good luck.