When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
This isn't for my 928, it is on an 88 jeep Cherokee of my sons.
Just did an engine rebuild and started noticing a clattering noise.
This group has the most informative people of any list I have been on, so I'm hoping to not be to off topic and get some pointers as to what is causing this.
We pulled the head hoping to find a bad lifter. This is what we saw.
This is the worst of the cylinders.
The engine has about 150 miles on it now.
I am starting to suspect the machine shop work or the supplied parts, Pistons.. may be a problem. The cylinders were bored .040 over. They say they measured all the bores and the Pistons for proper clearance.
I'm no expert, but the first thing I would check is the ring gap. The major scoring looks like the top ring might have bound up from a too-small gap. But that's just a guess, looking forward to how this develops.
I checked the ring gaps, .015 was what I measured and that was within the spec.
Thanks though, I am looking for anything that I may have done wrong as well as of course things that don't point to it being my fault.
I also checked that the rings did not protrude from the piston grooves.
Unless a newly rebuilt engine is more prone to scoring with overheating, I have probably changed the coolant in this vehicle 10 - 15 times over the years and never had an over heating issue.
The cylinders, after 276,000 miles looked better than this, after 150 miles. We did the rebuild because the oil pressure had dropped way off due to crankshaft bearing clearances.
Right now, I wish I had just slapped in a new set of bearings and put it back together.
The Shop mentioned overheating. We watched the head temps very closely. I had thermo-couples on the head. The head never got above ~197.
Temp gauge never showed hot.
I am also questioning the piston to cylinder wall clearance. The shop verified the pistons matched the bore for clearance.
We were very careful of overheating and monitored the head temp closely. Filled system and ran to thermostat opening. Let it cool and added coolant until at proper level. Started it up and coolant level was good, temp good started the break-in procedure.
150 miles in started noticing the clattering and started investigating.
Ken, did you put the pistons back in or did the shop do it for you? The wear is in an odd place for anything other than skirt wear. That usually happens when there isn't enough clearance or the piston got big from overheating.
The second option is that the pistons are in backwards, so the wrist pin and any connecting rod offset is wrong. That makes a sound called piston slap, a sound that changes as load changes.
Regardless, the pistons need to come out. Once you get them out you'll see immediately where the scuffs are and the condition of the rings. You'll also have the opportunity to measure the pistons and the holes to verify basic clearances.
The pistons all have front marked on them with the offset towards the right side.
They were all put in with the arrow pointing forward.
There is wear on the piston skirts corresponding to the cylinder wear.
The rings look good. There is even some wear on the piston above the rings. In line with the skirts. The wear is only on the sides. It is not on the front or rear of the cylinders.
There is obvious skirt wear.
We were watching head temps very carefully, We never saw a temp above 197 except near the exhaust ports. There the temp was around 218. Near the intake ports the temps were around 208. The other side of the head, the temp was around 195.
I really doubt overheating. But I am looking for likely causes.
The spec for bore to piston clearance is;
Piston-to-bore clearance.
Desired. 0.0013 to 0.0015 inch.
Allowable. 0.0008 to 0.0015 inch.
I told the shop that I did not check the piston to bore clearance and they indicated that they did before I picked up the block and pistons.
Looks to be a cast iron block. The specs for the bore to piston clearance seems very small. If I had bored that engine I would definitely not go smaller than the upper limit of the specs (.0015"). What pistons were installed? If aftermarket pistons not made of low expansion aluminum alloy were installed, the clearance need to be increased.
Åke
Last edited by Strosek Ultra; 02-20-2017 at 05:47 AM.
The installed pistons were after market Sealed Power.
They list the minimum spec as .001, the shop did the measurements and installed the core plugs and oil galley plugs.
The shop cleaned the bores and lightly oiled them ready for piston install.
So I wiped them down and then oiled the cylinders as part of the piston install.
I did check that the pistons moved freely on the wrist pins. No binding.
I called Federal-Mogul and they said it was caused by either a;
1 - Dirty build, the shop confirmed they washed the bores down with hot soapy water.
2 - Tolerance to tight, I don't have the right bore gauges to check, and it may be to late with the wear right now. Maybe I need to buy a bore gauge set. Any recommendations?
3 - Bore out of round, again the shop measured and I done have a accurate enough tool.
4 - Running to rich and fuel washing down the cylinders. It didn't feel like it was running rich. O2 and computer controlled, also did not smell rich at all. I don't think it is this.
I am starting to think about removing a variable or two and going to a different shop and getting some bore gauges and doing my own verification of clean cylinders.
02-19-2017, 08:10 PM
What causes cylinder scoring
