(I also posted this threat on the FE forum but any hambers info is welcome) I found out my 5 out off 8 pistons have cracks in theme some are small but one piston is cracked from down by the skirt all the way up to the bottom ring. See photo's. also, in 3 cylinders the upper ring is broken. What caused this piston failure? The book says the cracks are due to piston to bore clearance.... Other info: '64 390 Merc Super Marauder 9.2 to 1 odo reads 65000 (165000?) Thanks, Ramon
detonation - preignition can and will cause piston cracking like this. Maybe caused by too much advance, poor grade of gas, water is gas...etc
The motor did run very well. I asume that with to much preignition the engine would not run that nice. The gas i'm running here in Holland is good up to 10.5. I sure hope it's not the piston to bore clearance, don't feel like spending a lot euro's on the cylinder boring.
x3. It can still be running great with too much lead in on the ignition and if the pipes are a little loud you wouldn't notice. Also what kind of pistons?
I did the timing adjustment "by ear". Since my timing pointer and balancer didn't match... So it could be the timing (sure hope so)... Pistons are bone stock, '64 ford.
Looks like expansion cracks, too tight a fit. Was it redone at some time? Cracks like that usually show up in a lot less than 65000 miles. The scored skirts are additional evidence of too little clearance. BTW, A Super Marauder should have a 427 in it.
I've got to agree with the detonation/preignition as well. The broken top rings also suggests it. Also not unusual to find this in a stock engine with high mileage. What kind of cylinder wall wear do you have. If it's bad you will need to bore anyway. I sure would'nt put a new set of pistons in with worn cylinder walls. The rebore shouldn't cost any more than the pistons.
Looks to me like that engine sat idle for a while....then was started and run. Stock Cast pistons.......can't expect too much. Mark
i pulled apart a 70k ho305 chevy motor that had some blow by. Motor ran good just a bit of smoke on start up. 7 out of 8 pistons were cracked, 20 psi on 3 cylinders. Cracked all the way across the face and down the skirts. Cast sucks!
It is very typical expecially in these motor to see cracked pistons when skirt clearance become excesssive. Basically the piston doesnt get close enuf to the wall to get rid of the heat. poor gas quality and igniton timing contribute as well. I think I have seen more cracked FE pistons then any other engine in my 45 years swinging wrenches. I dont mean hundreds either but of all the cracked pistons I have seen that is the most number that were FEs. Often after a no rebore rebuild too. In fact just a few days ago i posted something about that in another vien. When we did budget 300 ford sixes for racing (hi on desire low on cash) we used to hunt for FE guys with cracked pistons as we could usually get 6 good ones out of a set , bore the 300 to 4.050" Pin size is the same and weight is exact to the gram. Higher compression. This car in this picture has a set of six from such a disaster. The guy we got them from did a no rebore rebuild (390 Bronco.) but put in new pistons for some unknown reason and cracked a couple. The block was worn not the pistons per say. After he rebored and fixed the clearance problem it was fine. We got them for $50. They were about 3 weeks old. That was about 1991 and I happen to know where they are today (still good BTW>) I dye checked the ones we bought and they were still good. Don
Excessive piston to bore clearance gets my vote. Looks like the engine is also running without an air cleaner judging by the score marks on the pistons.
The book is correct, EXCESSIVE piston to wall clearance. Cast pistons are designed to be set up and run with much tighter P-T-W clearance than a Forged piston. One reason is just by the metalurgy of a casting, they are not designed to sustain rocking and side loads impacts for lack of better terms. Ever see the metal strips cast inside of a cast piston? Ever drop a cast crank on the floor, usually end up with 3 little cranks. Very cold in the Netherlands too, start a very cold engine with cast pistons, before it reaches temp, and maybe race it up a bit, result an easily cracked piston skirt. BDM
I would tend to agree with Tedd on this one. Too much skirt clearance. Detonation will crack between the rings and knock the top of the piston out. Just pulled apart a 300 six that had the ring lands cracked and broken top rings, the old guy that owns it pulls a 32' travel trailer over Questa grade wide open in second gear on a regular basis. He must turn up the radio when the engine is crying out for relief.
Yep and if you turn the piston over you will see the steel strut that is cast into the piston. Crack is usually right were the steel and the aluminum intersect. The steel strut is the only thing that's holding it together. Pretty normal on a Ford >>>>.
THe Cardinal shipping guy here has dropped three for my pals machine shop when they come back from the grinder. He caught him on the last one and opened it before he left. two piece crank! The guy didnt seem to care. they no longer use him. Don
I didn't say it couldn't be done just that you would need to drop it pretty hard, those delivery guys can get pretty rough. I've had them break bell housings, trans cases and cylinder heads, they never seem to care and wont pay up even if you but extra insurance.
For balancing flywheels, flexplates, couplers, and pressure plates we had a real nice inline 6 Chevy crank that we would use on the balancer. The in line 6 cylinder being neutral balance. Combine that with a " new " guy, one drop to the floor, and we now we have 3- two cylinder chevy cranks,
Its just old and time for a good rebuild there is excessive clearance, also the piston design is quite bad if you notice the crack in the piston will run up to the edge of the oil return slot located in the oil ring groove that is a cast in groove and a weak point for tracking. A better design piston will be holes machined in the groove for oil return. Also remember after a fresh cylinder bore, to turn the engine over while on the stand and with a die grinder and sand disc to put a small radius on the bottom of the cylinder to get that evil sharp edge off and will minimize the scoring on the skirts. Alot of people forget to do this usually a machine shop will not, that sharp edge will score the hell out of the piston and scrape the oil off the skirts. Note oil return holes
I was surprised it broke that easy myself. It was a Poncho crank i saw but he said he had two others which is why he was watching the guy. Probably depends a lot too how they hit. The insurance thing was a nightmare. He found a work around but I dont think i could have done that. Had to fudge the story a bit and bank on the idea that the driver would never tell his supervisor about it. Anyway Enuf about that. Back to the cracked pistons. Don
To the O/P, you mentioned the issues of Euros being not in abundance. You need pistons anyway, now the forged are much more expensive BUT, if you have a GOOD machinist, you MIGHT very well get by with a hone on the cylinders and not a bore. Only the machinist can tell you. If the bores are relatively striaght, round, and not too much taper, ALL 3 are important, you might be able to save them with just a hone. Lets say the new FORGED pistons spec a .004" piston to wall, can you run them at say .007", absolutely. Guy's this is not to start a pissing match, because it gets done all the time, and on race engines everywhere. I personally freshened up a 565 once all out race engine, pistons were CUSTOM DOMED JE's, meaning not off the JE shelf. These pistons were close to $1000, and required 3 weeks to machine if I wanted a set .005" over. Long story short, the customer signed off of all liability to me, and they were run at .011" - .012" piston to wall. The engine finished all the races without failure. Mind you the bores were finished to plus or minus .0001" for taper, and out of round. BDM
I'd check the bores, if ok, scratch em up with a ball hone, throw a set of cast moly rings in it on some cheap slugs and run the hell out of it.
It IS 46 yrs old guys. If it's not too loose I'd agree with lippy on this one. Watch the ring gap also.
Yeah guys, I know, not the best way...... But with no timing pointer and no numbers what so ever on the balancer it's the best I could do. And it was running great
The Jalopy Journal
