I've never rebuilt a Ford engine ....: Grassroots Motorsports forum: Grassroots Motorsports Magazine

Subscribe get a full year for only $23.95 Sample Free Test Drive—no strings attached

July 12, 2011 1:15 p.m. 914Driver SuperDork

..however, they're all just nuts & bolts, right?

My friend is helping his 17 year old built a 351 engine for a 1971 Mustang. He asked me about installing the pistons because they seem tight on the crank. By his description, the crank doesn't spin as freely as I would like to see, but with each piston & rod installation it gets worse. He has to use a breaker. He's lubing it with Lucas synthetic assembly lube.

The cylinders have been bored .010 over and honed, new rings, bearings etc. and the crank has been polished. I asked if he used Plasti-Gage to see the tolerance between cap and journal and he said no. The machine shop that did the work and line bored the crank and cam, said everything was fine.

Tight tolerance, incorrect thrust bearing?

Dan
July 12, 2011 1:20 p.m. Javelin SuperDork

Disassemble immediately! Some clearance is definitely incorrect. The last Ford that I saw do that was actually rings that were too large/not enough gap.

He needs to check tolerances with the plasti-gage. Measure, measure, measure!
July 12, 2011 1:28 p.m. 914Driver SuperDork

racinginc215 wrote:

make sure rods are in the right holes.

8 rods, 8 different lengths?
July 12, 2011 1:32 p.m. 914Driver SuperDork

I just talked to John, he said the crank was tight as soon as you torqued the caps down.

Plasti-Gage!!!
July 12, 2011 1:50 p.m. fasted58 HalfDork

If the crank has never been cut and is in spec the correct brg would be STD and should be stamped on back side of brg half.
July 12, 2011 2:00 p.m. ClemSparks SuperDork

You've probably already thought of this, but I'll throw it out for posterity:

Make sure the rod bearing is staying clear of the fillet on the crank. I put some rods in with the non-clearance side of the bearing buried against the fillet on the crank. It got real tight real quick.

Clem
July 12, 2011 3:35 p.m. mad_machine SuperDork

I definatly second (or third, fourth, or fifth) the crank bearings being wrong
July 12, 2011 3:49 p.m. egnorant Dork

Piston drag? It will get harder to turn with each set of pistons added to the crank.

How tight is too tight? I really couldn't say, but a worn 390 with no heads that I worked on recently still required a bar and a bit of grunt to turn the crank.

Bruce

P.S. When in doubt, recheck your clearances.
July 12, 2011 6:03 p.m. iceracer SuperDork

The crank should turn freely with out the rods installed. Some thing definitely is wrong. As a number of people have said.
July 12, 2011 11:11 p.m. Streetwiseguy Dork

Main caps in the right spots, not backwards? Pistons upside down? Oil rings not compressed properly, folded over? Normal drag with the rear seal in place?
July 13, 2011 3:51 p.m. jimbbski Reader

I agree with all ideas already mentioned but on the engines that I built there was enough drag that I did need a breaker bar to turn over the engine. What with the rings, rod bearings, and mains you can build up quite of bit of drag!
July 13, 2011 4:06 p.m. fasted58 HalfDork

Some manuals provide a max torque for turning over the rotating assembly at the crank w/ new brgs, pistons and rings. Over the max torque you have trouble.
July 13, 2011 7:53 p.m. Curmudgeon SuperDork

When a crank is in the block with the caps torqued, you should be able to turn it by hand. Once the rods and pistons are installed, the only drag should be the rings. I heard a max torque of 20 foot pounds for a V8 somewhere, about as much as the average 6mm thread bolt will take before risking breakage.

I helped a guy build a hipo 302 a few years back, when we got the pistons/rods back from the machine shop we discovered 4 were on backwards. So no machine shops are NOT infallible!

Once the recip assembly (crank/rods/pistons) is in place, you should be able to move each rod side to side a slight amount with your fingers. If it won't move, investigate. It's so easy to put a rod cap on backwards or even worse... I helped a guy with a 400 Pontiac many years ago, when he took it apart he just took the caps off the rods and chucked them in a box. No markings etc. We spent a whole afternoon swapping caps with rods and test fitting them on the crank one at a time to see if they bound up. Talk about a pain in the ass.
July 13, 2011 8:17 p.m. fasted58 HalfDork

In reply to Curmudgeon:

Just talking about that at my buddys engine machine shop this afternoon... guys bringing in a box of loose, unmarked rod n main caps. Number punches are cheap, mark rod and main caps while installed.. EZ, saves a lotta headaches.

Plus, he just got back a crank for an antique tractor engine that that was cut 0.020, #6 was only cut 0.015. E36 M3 happens.
July 14, 2011 8:44 a.m. 914Driver SuperDork

Update:

John had his son take it all apart and noticed the Haynes-Chilton book on the bench. "What's the book say?"

"Well, I got this sheet off the Internet ...."

Read the book, don't just look at the pictures and skim read, KNOW it.

The thrust bearing was mislocated. After proper reassembly the crank spun like a top.

Last night the son put the pistons in, after four it wouldn't turn anymore.

See those maks on top of the piston, do you know what they are?

"Yeah, that's where you squirt oil, right?"

What's the book say?

Oops, they're facing the wrong way.

We've all been 17, we've all been exposed to new experiences. He's coming along....

Dan
July 14, 2011 6:58 p.m. mad_machine SuperDork

that is one way to teach them:)
July 15, 2011 9:11 a.m. Rusted_Busted_Spit Dork

I think thats the best way to learn. when I drive my Spit into my future FILs garage I knew crap about working on cars. After 2 weeks of late night with him I had a real good start.
July 15, 2011 3:17 p.m. 4eyes HalfDork

Most machine shops are staffed with Chevy guys. They work on Ford, Dodge, and them furrin' engines with contempt. Check E V E R Y T H I N G

I could tell you stories that would curl your toenails.