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| Piston scuffed the cylinder https://slantsix.org/forum/viewtopic.php?t=68742 |
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| Author: | Sacandaga [ Tue Sep 01, 2026 7:52 pm ] |
| Post subject: | Piston scuffed the cylinder |
Hello all i have an 85 truck slant six. I didnt know anything about this engine so i tore it down to inspect. I discovered the cylinders still show the cross-hatch. Very little if any ring ridge. Rod bearings look excellent, I havent inspected the crank bearings yet. The problems i have found is that the cam lobes on number 6 are pitted, no rust. The rest of the cam looks great. Pitting is so deep on 6 that im not going to use the cam. The next is the number 6 cylinder and piston. The number 6 cylinder is scuffed vertically in several places, not very deep, just marks on the cylinder walls. The sides of the number 6 piston is scuffed as you can see from the pictures and theres a small section where the piston is missing some material above the top ring. The top of the piston looks normal. When i first started tearing down the engine i pulled the head off and was looking in the cylinders to see if the pistons were centered in the bores. All of the pistons were nicely centered and had approximately the same distance between the piston and the cylinder, except for number 6 of course. Number 6 had no gap between the piston and the cylinder on the side that was missing the material and a larger than normal gap on the opposite side. I plan on putting in a new or used cam and a used piston/rod assembly and run the engine. But what happened to the cam and number 6 piston? https://postimage.me/image/1000003997.SNt8z https://postimage.me/image/1000003993.SNt15 https://postimage.me/image/1000003992.SN6Ax https://postimage.me/image/1000003998.SN6D6 |
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| Author: | mcnoople [ Wed Sep 02, 2026 9:09 am ] |
| Post subject: | Re: Piston scuffed the cylinder |
do you have any pictures of the bore? I have seen an engine run with cylinders that were rougher than 40 grit sandpaper. It was very noisy. The story on that engine was that it was an aluminum v6 (acura j37) with NO cylinder liners/sleeve. The engine was designed with aluminum cylinder walls. Those are decently reliable engines except the one I mention ate all the ceramic and electrode from a failed iridium spark plug. After the tear down the customer just wanted a piston and that is what he got....new piston in a bore that was impossibly badly worn. The wear in your picture wouldn't worry me if the bore itself is still in good condition. You want to check the bore for taper and whether it is actually round. This requires some measuring tools and there youtube videos on how to do it. If the bore is decent I would find another piston for that hole and run it. I didn't actually watch this video I am linking, but the channel has a past history of decent content so I link it as an example only. https://www.youtube.com/watch?v=1vejKSxzGC8 |
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| Author: | Jase [ Wed Sep 02, 2026 5:19 pm ] |
| Post subject: | Re: Piston scuffed the cylinder |
Regarding the camshaft. Likely that it can be reground! The BENEFIT and reason to do this is purely for the wellbeing of the Oil pump drive gear. Putting a new or different cam in the engine puts the oil pump drive gear at risk of accelerated wear, and then you have no oil pressure.. sometimes in very short order. It happens quickly, and in my opinion not worth the risk.. and you get more lift and slightly better performance as a side benefit... From this perspective the original camshaft and original oil pump drive gear might be the most valuable parts on the whole engine.. Because everything else is easier to replace or repair. |
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| Author: | Killer6 [ Wed Sep 02, 2026 7:25 pm ] |
| Post subject: | Re: Piston scuffed the cylinder |
Quote:
Hello all i have an 85 truck slant six. I didnt know anything about this engine so i tore it down to inspect. I discovered the cylinders still show the cross-hatch, no unusual wear. Very little if any ring ridge. Rod bearings look excellent, I havent inspected the crank bearings yet. The problems i have found is that the cam lobes on number 6 are badly pitted, no rust. The rest of the cam looks great. Pitting is so deep on 6 that im not going to use the cam. The next is the number 6 cylinder and piston. The number 6 cylinder is scuffed vertically in several places, not very deep, just marks on the cylinder walls. The sides of the number 6 piston is scuffed as you can see from the pictures and theres a small section where the piston is missing some material above the top ring. The top of the piston looks normal.
The piston overheated pretty good, the rings are seized/pinched, question is....why? Rings possibly carbon seized and caused it, or cyl.6 ran hot for some reason,....head gasket in good shape?......holes at the front of the block closed as they should be?.......if not #6 may have starved for enough cooling.
When i first started tearing down the engine i pulled the head off and was looking in the cylinders to see if the pistons were centered in the bores. All of the pistons were nicely centered and had approximately the same distance between the piston and the cylinder, except for number 6 of course. Number 6 had no gap between the piston and the cylinder on the side that was missing the material and a larger than normal gap on the opposite side. I plan on putting in a new or used cam and a used piston/rod assembly and run the engine. But what happened to the cam and number 6 piston? https://postimage.me/image/1000003997.SNt8z https://postimage.me/image/1000003993.SNt15 https://postimage.me/image/1000003992.SN6Ax https://postimage.me/image/1000003998.SN6D6 |
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| Author: | Sacandaga [ Fri Sep 04, 2026 8:39 am ] |
| Post subject: | Re: Piston scuffed the cylinder |
How much would a cam/lifter regrind cost? Nothing radical just a max torque build. Its going in an 81 w150 stepside with an np435. I actually thought about replacing the oil pump as well and putting in a high volume unit, if i can find one. Cam pictures. First link starts at number 1. Last link ends at number 6. https://postimage.me/image/1000004074.SThiC https://postimage.me/image/1000004075.STh0c https://postimage.me/image/1000004076.STh1u https://postimage.me/image/1000004077.STh8Z I oiled cylinders 1-5 and cleaned number 6 to get some pictures. I will probably end up honing number 6. I couldnt feel any of the vertical lines with my finger but some were just barely able to catch a nail. Also cylinders 1-5 about 1.5" - 2" down into the bores from the deck, they all had the same wear mark. Not enough to catch a nail on. See the first link. Link two shows number 6 cylinder and some of the missing material from the piston that had transferred and stuck to the top of the bore. Its hard to capture the lines in number 6 because of the reflection. https://postimage.me/image/1000004052.STSwq https://postimage.me/image/1000004054.STSbD https://postimage.me/image/1000004057.STSc1 https://postimage.me/image/1000004061.STLGX https://postimage.me/image/1000004062.STLOK https://postimage.me/image/1000004063.STLZI I do agree that it was likely overheated. When i took the pan off it had maybe 2 quarts of oil in it and the smell reminded me of hot electronics. |
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| Author: | mcnoople [ Fri Sep 04, 2026 10:51 am ] |
| Post subject: | Re: Piston scuffed the cylinder |
google "oregon cam grinding" and give them a call for a regrind price. They are known to the community and will help with choosing specs. |
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| Author: | Dart270 [ Fri Sep 04, 2026 10:55 am ] |
| Post subject: | Re: Piston scuffed the cylinder |
If your oil pump is making good pressure, do not touch it and reuse it as is. New pumps have unknown gear quality and they can fail and shred your engine. Oregon cams can do a regrind for about $125 plus shipping the cam core to and from them. Great folks. I can recommend a good grind, and likely their "RDP" grind is best (2106R, IIRC?). Lou |
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