pistons seizing in block, 170 cid Ford, long post

aribert

Well-known member
First time to post, though I have lurked off and on for several years - mostly on the Ozz engine list.

I have had this problem twice now - engine begins to seize shortly after being rebuilt.

Rebuilt my Ford 170 (250K miles on engine and not the first time that I've rebuilt it); 0.040 over on bore, crank ground, rods reconditioned, Clifford Cam, head: milled approx 0.060 (47cc combustion chamber size), largest intake and exhaust valves from 250 cid, port divider...., rotating parts dynamically balanced. My Falcon was undergoing its qtr million mile renovation and so the engine saw lots of idling time before the car was complete enough to drive on the street. First 150 miles of driving on surface streets - stop & go - prior to freeway use. At 190 total miles of driving, while on the freeway, the engine began to loose power and sound rough (as if the timing had slipped - my initial diagosis as I was slowing down to exit the freeway). By the time I shut it down it was clattereing like a spun rod bearing. Tear down showed serious galling of the piston to block in 3 cylinders. Initial wear appears to have started over the width of the piston skirts. The consensus amoungst those that I discussed/showed the damaged parts to was that the prolonged idling at break-in was the culprit.

Replaced block with '65 170, block bored 0.020, new Silvo-lite (sp) pistons, reused all other dynamic parts & head from the '61 engine. Broke the new enigne in by the book. At 290 miles the second engine began to loose power. I got this one shut down a bit sooner and the damage was not as severe but still some of the pistons had significant wear. One bore had grooves about 0.015 deep, two other bores had the cross hatching worn away but no grooves.


Now I have aquired a '66 200. After pissing away over $2000 on the first two engines, I am simplying reringing, new bearings & timing chain - all tolerances are near the high (loose) limit. I don't want this problem again and I certainly do not want to pull an engine out of my very nicely painted engine compartment for the 3rd time!

I have yet to figure out the cause of the failures. Major parts shared between the two engines: head, crank, rods, cam. I am down to one possible cause but I find it doubltfull - I'm refraining from posting that speculation until you have given it some thought and hopefully responded. Thanks for reading this long post - speculation gladly accepted.
 
Personally, I don't think the idling thing was the problem. But a few of thoughts...

(1) (the obvious one) piston/bore clearance was tighter than piston maker's specification. Was the final hone dimension confirmed?
(2) Bad machining- any possibility that the bores were bored/honed with a taper? Or bored out of square to the crank?
(3) Bent rods? Were the pin holes checked for square against the crank holes? But this one usually trashes bearings, too.
(4) Rings- Were the ring gaps checked for proper tolerance in both the top and bottom of the bore? Were the rings checked for proper clearance in the ring grooves? Were the ring grooves the proper depth for the rings? Were the oil ring pieces assembled/installed correctly?
(5) Any possibility of overheating?

Other less likely possibilities come to mind but these are the big ones...
 
Other things to check:

  • Rings installed upside down

    Rings have insufficient end gap

    Rods installed backward. Only a problem if the rods had oiling holes. They should face the thrust side of the bore.
But If the pistons were siezing the culprit is probably insufficient piston to bore clearance. For cast pistions, it should be about .002" (don't have my manual here with me)
 
Thanks for the replys. So far, I think that I had checked everything prior to assy of both engines.

I checked end gap of rings in the bores, both top and bottom of bore. I checked bore dia with a telescoping gage and mic. I did this several times to minimize error on the gage but I suspect that I could easily have .0005 error using that set up. FWIW, I know the second block was bored with out the main caps installed. THe two blocks were bored out at diffferent shops (first shop I have used for about 5 or 6 previous (other brand engines) block boring and time wise about 4 years apart between the first '61 170 rebuild (bored 0.040 over) and its failure and subsequent rebuild of the '65 block bored 0.020 over (car was down for a 2 year renovation that ended up taking 8 years).

Rings were installed per ring mfg notes / markings.

I checked rod orientation at tear down and all rods had the oil squirt hole correct to the front of piston notch.

Bent rod: the old 170 engine (prior to rebuild) had a visibly bent rod and I suffered for 125K miles with an intense driveline vibration that I could never find (my back/butt would get numb after half an hour driving at freeway speeds, BTW the old rod brg on the bent rod showed no unusual wear for a 125K engine!)

Ring groove depth appears to be correct on the pistons but I would need Silvo-lite's (sp) dwg to confirm. Have there been any issues with a bad batch of pistons from Silvo-lite? I do not remember the mfg of the pistons on the first engine but they look identical (casting features on the underside of the piston) to the Silvo-lites used on the second engine.

I do not think the engine over heated. I am limited to the stock temp gage but it appeared normal. As the engine was starting to seize, the temp started to rise but it did not peg the gage nor begin to boil over before I got the engine shut down. For fear of hot spots, I did not bother to attempt to have the first block rebored to .060.

If the pistons are not at fault, one other common item between both engines is the head (and I am planning on reusing the head - a lot of effort went into smoothing out the transitions between the log and the inlet runners). My goal in milling the head was to get at a low 9.x to 1 CR. I never heard any pre-ignition detonation/pingin sounds nor was there any sign of piston top errosion, and I am familier with pre-ingition as I have a Triumph 6 cyl that I bumped the CR up a bit too much to run on 87 octane. Is it possible that the local temp on the pison tops was too high, causing the pistons to grow excessively and start wearing into the bore? I am rapidly running out of speculative theories. Also I was still running the stock carb as jetted. I did a couple of plug readings and everything looked good (and since I did not hear any pinging I did not consider opening up the jets). Eventually, I intend to use a Weber 32/36 DGV carb but want to get everything else settled in prior to doing that.
 
MustangSix":2m7bgn06 said:
Other things to check:

  • Rings installed upside down

    Rings have insufficient end gap

    Rods installed backward. Only a problem if the rods had oiling holes. They should face the thrust side of the bore.
But If the pistons were siezing the culprit is probably insufficient piston to bore clearance. For cast pistions, it should be about .002" (don't have my manual here with me)

My Haynes manual for my '80 Stang says 0.0013" - 0.0021"
 
At its most basic level, any bearing failure is from a failure to lubricate. It may fail to lubricate for many reasons, such as throwing a handful of sand in the bearing, which no one would expect to give proper lubrication. And a piston/cylinder is really just a reciprocating bearing surface. In my business (Saw filing) we run thin kerf circular saws with babbit guides at over 4000 rpm in some of our edgers. About the worst thing you can do to them besides turning off the lube is to run the clearances too tight. I just have to think that's what happened to your pistons, too little clearance for your particular combination. Depending on the manufacturer, the co-efficient of expansion can vary quite a bit on piston materials, so even if it was set up "by the book" it wasn't enough. I always check mine with a feeler guage just to be sure.
Lazy JW
 
How does the oil get to the piston skirts? Could a lack of oiling between block and piston cause excessive heat, therefore galling? :?
 
8)

On my 2.3L there is a small hole drilled in the long part of the rod cap. It is at an angle so that when the holes line up the oil pressure squirts a bit of oil on the thrust side of the block. And if it doesnt have one you can do one. My dads '75 Pinto 2.3L didnt have one and he and my grandfather modified all the rods so they all squirted oil on the cylinder walls.

I also really like the idea of dry film lube on the piston skirts.
 
Howdy Aribert and All:

What a great mystery. Thanks for the great detailed description of your situation.

I'm wondering about bore distortion on torqueing the head down. Ideally, it would be best to bore and hone any thin wall cast block with a torque plate and main bearing caps in place. Torque plates for our engines are rare. Both boring and milling the head lessen the structural integrety (stiffness) of the components. If the torqueing process were done in a hurried, once and for all, fashion, or head bolts or hole were not well prepared and lubed, any of these things could add to a distortion problem.

If cylinder wall distortion was part of these two cases, the tightest areas would be on the upper end of the bores and nearest the head bolts. The cylinder wall would distort in a four leaf clover pattern with waisting pinched in adjacent to the head bolts. Heat build up would quickly move to the thrust side (greates presure)and to the pin/skirt (least cooling) areas. Once heat build up starts it is very difficult to identify it's origin. The piston/cylinder that seized is probably too far gone to analyze the origin of the problem, so check the others, paticularly adjacent cylinders and pistons.

Another consideration is that you were one of the unluckiest engine rebuilders in the world by finding two blocks that were cast with some degree of core shift during the molding process. Take a look into the water pump recess of the roasted blocks to see how well the mold lines line up. This is a very rare problem on later blocks, but more likely on early ones.

Please look over the wasted block for damage nearest the top and nearest the head bolt corners. I'm most curious.

Adios, David
 
Just some info,

Benson's machine in Sants Ana, CA has a 200 torqe plate for boring blocks.

Todd
 
Ya'll are scaring me!!!!

seriously... I am getting more nervous reading this post.
 
Stop worrying, Jimbo.

I've never used a torque plate on a 200. No machine shop here has one and it would cost too much to make one.

It would be nice, but it's not critical unless you are blueprinting the engine and won't cause the thing to sieze up as long as you are within spec on the final bore.

Another thing that occured to me was that this might be a carb problem. If the carb is somehow flooding the engine, it could cause washdown and the pistons would experience accelerated wear. I've seen that happen on several engines.
 
I am not freaking or anything... but still this sounds bad... sorry to hear 'bout that....
 
THanks for the replys. If the carb was flooding shouldn't it be noticeable on a plug reading or as a soot cloud out the exhaust when accelerating? There was a (very) little carbon on the piston tops, I assumed it was from the assembly lube frying and with only 290 miles on the engine that it had not burned off completely. Carb was kitted at the rebuild and this is the same carb that has been on the engine for atleast the last 130K miles (car has been in the family since '65). One of my thoughts is that I was running a bit too lean (hot) combined with the higher CR that was causing the pistons to expand too much. Mind you I watched the temp gage and did not notice that the engine was too hot nor did it ping on acceleration nor was there any visible errosion on the piston tops that would imply pre-ignition.

Dennis S. I looked into the water jacket via the water pump both of the damaged blocks and did not see any mismatch in the cores - not that I actually was able to see any core parting lines in either water jacket. Other than the stripe damage menioned below, I saw no unusual wear that would indicate that the bores were not round due to disortion.

I looked at the 2nd engnie parts again last night (car is in my workshop garage about 10 miles from home). Because I was able to recognise the problem sooner on the second engine, I was able to shut it down a bit earlier and there is less damage. On most of the bores there is a burnished/polished stripe the width of the piston skirt (3/4 in.). BY burnished I mean that the surface is exceptionaly smooth, the honeing cross hatching is eitther gone are almost completely gone and the stripe is very shiney (sp). On the #6 piston there was a pair of damaged (galling) stripes (about 0.010 -0.015 deep vertical scratches) on either side of the burnished stripe. so that the total width of the 3 stripes was about 2 in. The wrist pin in the #6 piston is frozen in place from heat distortion on the piston and there is significant surface damage to the piston. The remaining 5 pistons have slight wear / polishing of the machined surface on the skirts that is slightly wider that the skirt tip. THe wrist pins rotate freely in these pistons. THe first failed engine had 3 seriously damaged bores/pistons.
 
Thanks for the post. I would tend to agree with scuffing as the culprit but I checked the rod bearing hole relative to the oil squirt hole in the rod that squirts oil to the underside of the piston and onto the bore wall. All rod bearing shells were correctly installed and the passage way was completely clear in all the rods. I had also run a round bristle brush thru every oil galley in both the block and the crank prior to assembly of the second engine. For the (now) third engine, I intend to prime the oil galleys from a bucket suspended under the engine, while turning the crank, prior to installing the oil pan, so that I can see oil coming out everywhere. The only common internal parts to the previous failed engines will be the head (and carb).

For the third engine I will reuse the original pistons/rods and crank and will have a very loose engine as the critical tolerances are at the high limit.
 
It's possible that a carb with a high float setting or a leaky needle could dribble fuel when the engine is off, yet still run well enough to burn off any excess deposits after start up. A leaking fuel injector will exhibit the same symptoms.
 
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