scuffed pistons, starting over

[highstumpr]

Anyone have a failure from piston scuffing with 4.2 rods using 677p pistons in their stroker? I should have my KB944s tomorrow, going with 4.0 rods this time.

[John]

How about a little more info. How many miles were on those pistons before the problems showed up. 677's and 4.2 rods have been used several times in different builds. Pic's would be great. If you could CC the KB pistons before you build, we would really be interested in the results/measurements.
Thanks
John

[highstumpr]

I will get cc and pin height measurements of new pistons in next day or two, as well as any measurements I can from the failure. What I know now is: #1 I should have done all the research myself last year so I'd know more about what I have now, my fault. 4.2 crank, 4.2 rods,677p, surfaced head now 56cc, they gave me the wrong intake gasket to port match my 92 intake so had to open head port to match, I don't know deck height, or quench, scr around 9.8/1 they said, (yea, I'm involved this time!) ,crane 753941 dcr anyone? milled taper out of tb, 24# injectors, borla header, no cat, 2.5 exhaust,amsoil bypass filter 456 gears,32 in. tires, 2700-3300 rpm on freeway.

This is in a mj hauling my tools to logging jobs, 5200 lbs loaded, sea level to 6000 ft in any month.
First build ,cam nose hole covered by wrong washer, no oil to timing gear.At about 7000 miles, timing chain broke at speed on freeway, tried to restart a lot before I finally noticed rotor not turning. Builder changed timing set, cleaned teeth out of pan. I thought we should start over, his dime his call. Started up with dead cyl. Pulled head put in one new valve. By the way it ran great no pinging on 91, 17 to 18 mpg. 2000 miles later thrust bearing went and took crank with it. Still his dime,(lots of 0s) replaced everything but the cam including lifters checked out the head, was ok. The pistons were scuffed then and I thought well yea, sure lots of crap to swim through. So ,all new except cam. Started hearing an odd noise at start up around 12000 miles didn't last past warm up. Got worse but sounded more like belt or pulley noise, finally ran it without the belt and it wasn't that, so it's torn down again. My cubic dollars this time. Oh and the cam first lobe is now just starting to go. Total miles on cam 37-38000, pistons<30000. Yes I did break it in at 2000 for 20+ min. always have used Delo 400 15-40.

[dwg86]

Where the pistons scuffed on the thrust side only? Did the rod bearings have notches in them? If the pistons where only scuffed on the thrust side, it could be caused by the short rods. (but the short rods worked in the original 258 engine and the 258 lasted a long time) If the rod bearing didn't have notches in them maybe that contributed to the scuffed piston and cam failure by not lubing the cylinder and cam. Just a thought.

[John]

Indeed, if the builder used the bearings for the older design, could have contributed to the series of events.
John

[highstumpr]

Thanks for the input. What do I need to look for on the bearings. I Thought the notch located the bearing and keeps it from spinning?

[dwg86]

Yes there is a knotch that locates the bearing. There is also a small half round groove on each half of the rod bearings. This allows oil out of the bearing.around the rod bolt, and out a small hole on one the side of the rod to splash lubricate the cylinder and camshaft. Some new bearings don't have this groove. I don't know why.
When I start on my stroker, I will make these knotches if the new bearings don't have them.
Also make sure the piston is installed on the connecting rod correctly so that the oil will lubricate the cam and cylinder (Hole on rod on the same side as the cam).

[John]

You might want to read this from the FAQ section, viewtopic.php?f=27&t=53
John

[highstumpr]

I went and looked at my old bearings, they are not grooved. The Federal Mogul z63310CPA bearings listed in the FAQ are not grooved either. The builder said no one uses that in any motors any more, they oil from out of the sides of the bearing. Anyone know of a grooved bearing for this. I remember a post in one of the cam threads talking about the oil sling, squirt, hole and path around the bolt. I'll go read that again. Scuffed badly on thrust side slightly on other side. They are saying the piston is coming to far out of the bore at BDC, rocking and wiping the oil off.

[dwg86]

I think you will have to notch them yourself. I understand that some oil will come out around the sides of the bearings, but I, personally, would rather have the notched bearings to help lube the cylinders and cam. You might loose a little hp because of windage(probably not even enough to measure), but the added oil, I think, is more important for longevity.
Cast pistons run a pretty tight bore, so I don't know how much they will "rock" in the bores. The 258 engine used the same crank and rod set up that you are using, and where known to be a durable engine, and last a long time. The 2 pistons that I found that are made for the 258 have a compression distance of 1.633 and 1.581, so that pretty much matches the 4.0 piston that is used in the low budget 4.6 stroker(1.581, 1.585, and 1.592). So I don't see a problem with the pistons coming out of the cylinders at BDC. I have a set of 258 pistons that I took off of the rods that I have. I am going to match them up to a 4.0 piston if the local autozone or advance auto parts has one in stock. It might not be till later this week.

[highstumpr]

Does any one have the cyl. length for the two blocks? They didn't have a 4.2 at the shop to look at. I was wondering if at BDC the piston pin would be in the bore farther in the 4.2 block than the same crank/ rod in the 4.0 block. I'd like to see a picture of the (is it a hole or groove like the main) that I need to make.

[dwg86]

Its a hole.

[Flash]

I have been told that the cylinder or deck hight was just a little bit longer on the 258 then the 4.0L.

don't have any Deck number for the 258 but the 4.0L spec is in the "FAQ" section above.

Have you read the "KB944 Pistons" Thread?
Since your starting over, might be an option that you didn't have before.

Flash

[highstumpr]

They thought the 4.2 had a deck height that was higher, right. So that gives that piston more pin height, more stable in the bore at BDC? I have been reading the KB 944 thread and am going with those pistons this time. They may have gotten them today after I left. I don't have my 4.0 rods anymore so will get those and then get the #s we've all been waiting for.

[dwg86]

Where are you getting the KB's from. I just went to summitracing.com and entered uem-kb944030 in thier search. It came up with set of 8 pistons for $917.00!!!!!!! Something is wrong because it should be 6 piston set. If thats right, 917.00 divided by 8 equals 114.00 per piston. That would be $684.00 for a set of 6. I read someone got them 450.00... Where???