One bad cylinder - what to do

Hi all ! _ _ _ What to Do. Hmmm

Dal (D1947CJ2A) commented on Larry's kubota build thread about having a Dauntless V-6 with one bad cylinder, and had asked what to do with his engine.
I didn't want to comment to Dal on Larry's thread "because" !

   Because, I have difficulty leaving "one-liners", so I opted to start a discussion on "what to do" to Refurbish Dals engine:

   This did start as a PM to Dal, and then figured you guy's would have some interesting input.

   Below is my Suggestion -

Dal,
   I was just reading your comment on Larry's Kubota thread.

   I am not an 'expert' but, I did grow up in an engine machine shop as a kid.
My dad was part owner for 20-years. I have spent a lifetime "Refurbishing" engines as a hobby. Upon graduating high school in 1969, I went to the local jr college, and my dad went to work for GM as a parts-man for the next 20-years.
Therefore, I had the best mechanics in town at my disposal because dad knew every mechanic in town, and so did I. (the Chevy dealer had 9-line-mechs).

   Because you cannot afford a diesel-swap, what I would suggest is you go talk to 3 engine builders ( if available ). Ask them if they would recommend replacing just the one piston @ .010 over the already .030, or if they would recommend replacing all 4-pistons, which is more-money in their pocket.
   I say 3-engine builders, because some of them are pretty proud of their work, and may not be very informative. You are looking for someone who will take the time to work with you, and offer "alternatives" to your build.
Remember - it is your money being distributed, and you want to be happy.
Don't be upset when one builder is short on conversation, and tells you that he will only do a "complete-engine-rebuild". Sounds just like that fancy-dressed Real-Estate agent who wants your money, but doesn't want to work with you, "because" he is just Too-Busy selling high priced homes rather than low-budget homes of your affordability. Get the Picture !! Go with your Gut.

   Call around to a few of the piston vendors to see if they can give you a weight of the pistons they sell. If that data is available, then you can compare that to one of yours. I would get a .040 piston that is slightly heavier than your .030 pistons, and match the weight of the new piston to the existing ones.

   In all reality, the engine won't know the difference because all it is, is just an air-compressor that ignites fuel for power to the wheels.
Think about THIS: how many engines have the same compression in all cylinders ? Really, we hope they are all consistent, but we know that won't happen.
Your engine won't know the Difference either. While you have the engine tore down, I would suggest giving the valve-train a tune-up too, with a valve seat grind and possible valve-facing and lapping.

   We are "always" on a budget, and I see new sets of pistons for $100 here and there. So, in the long run, compare costs of 1-new piston, vs the cost of a new matching set and boring all 4-cylinders.

   Otto made some mention of boring and using Buick 350 pistons too. You might send Otto a PM to see what he suggests as a Fix. Or, he may chime in here to give us all his ideas which may be worth while to consider.

   Looking at this situation, if you were to replace one piston at .040, if the cylinder will clean up at that, you'd probably have to buy a Set of piston rings just to get rings for the one new .040 piston.

   Here is what I would do first before anything. The rust in the cylinder may just look-bad, but may clean-up better than you'd think. I have a 3-sided file that I have ground the point to a smooth taper. This becomes a rust scraper.
Carefully scrap the rust off the cylinder wall to inspect closely.
( all scraping must be perpendicular to the bore, not vertical scraping ).
I have found over the years that a cylinder hone is marginal at best, and it just hits the high-spots in a non-uniform manner. That's my opinion. Other folks may disagree, because we all have different techniques that work for us.

   Upon scraping all of the Rust off the cylinder wall, you then take 50-grit Emery-Cloth and tediously polish the cylinder walls to a shiny finish.
   ( I do this in a cross-hatch manner just like a Glaze-Breaking procedure ).

   Now get some 5-power hobbyist magnifier glasses ( I have 7-power ) and take a Close-Looksy at the condition of the walls to see if you have Pocking or shallow rust pockets or swayles. This is when you decide if you are happy with the clean up or if you think the cylinder surface is in need of an over-bore.
   At this point, you may try using a good cylinder hone and give it a go to see if it will clean up further. If you wind up honing it and you have increased the piston to wall clearance by .001 or .002, Who Cares ! right !
It is your engine, and I guarantee it will run fine with a little looser tolerances.
   We have to remember that Grandpa's Willys that has been knocking for the last 30-years was still dependable when tore down. Upon tear-down, we found the crank journal on #3 cylinder had worn completely through the bearing babbit material and through the steel backing on the bearing too. And it was still running and getting Grandpa around when disassembled. We sometimes become way too concerned about Bearing or Piston clearances.   my 2-cents.

   One thing about the File-scraper:   it cannot have a sharp point which can gouge the cast iron, so you want the point-end to be slightly rounded for no-gouging of the cast.   No, the file won't ruin your cylinder, and you are scraping off the heavy rust rather than sanding it off.
Another good scraping tool believe it or not, is the back-side of a hack-saw blade. these make good scrapers because they are hardened-steel and hold an edge real well for stubborn rust-scraping. If the going gets tough, you just use the edge with the teeth. Try it sometime, it Works !! real good.
   If you get a gram-scale, you could actually balance the weight of a new piston to the old one by grinding off excess material from around the piston pin boss. I am just injecting ideas to get the engine refurbished to useable condition without breaking-the-bank with a "full-rebuild."

   Remember, this is a Budget-Refurb and not a Total-Rebuild !

   Len (greaser007)