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Questions On Rebuilding A Turbo Block.

Discussion in 'Jeepster Commando and Commando Tech' started by Henry Nachtsheim, Nov 6, 2019.

  1. Nov 6, 2019
    Henry Nachtsheim

    Henry Nachtsheim New Member

    Mar 1, 2019
    I'm rebuilding a 231 for my jeepster, The tech #s show my block turns out to be a "turbo block" early 80s, to get compression up, using flat top pistons I can only find .60 over. My very able mechanic was questioning boring more than .30 over until we discovered the turbo aspect. My question's are; anyone know where i can get .30 over flat tops, or what's the feeling about boring the block to .60 over? Whats the difference in the turbo block than the standard 231 block? Should I stick with my 225 fly wheel? And where can I get a rebuilt odd fire crank? The jeepster is mostly used for running around the island I live on, not over 55' or creeping around the Glades at slower speeds.
  2. Nov 7, 2019

    Dauntless1971 Member

    Bend, OR
    Oct 22, 2004
    It would be interesting to see what the casting numbers of your odd fire turbo block, heads and crankshaft. My understanding is some early turbo engines used the same block as the N/A engines. I figure if you are building a even fire engine, just supply your machinist with the odd fire flywheel and have it balanced with the rest of the parts. Years ago I had a small block Chevy engine built and used flat tops pistons. I have regretted for many years trying to get more horsepower by raising the compression. As mentioned in your other post TA Perforce may be your only choice for a quality piston. Bay Burton may also have something, though it might still be a dished piston since it is designed for use with a turbo.
  3. Nov 9, 2019

    Keys5a Sponsor

    Florida Keys
    Jan 23, 2014
    If I recall from your other post, this turbo block 231 came out of a Jeepster parts chassis? I thought you said it was an odd-fire? The main difference between an odd and even fire is the crankshaft its self. The odd-fire rods share the same journal on the crank. The even-fire crank has a "split-pin" rod journal where each rod has a separate offset on the same journal.
    What crank do your have? The early 80s turbo Regal block was an even-fire engine. The 231 odd-fire engines were only used from '75-'77, and they are essentially "bored-out" 225s, with some improvements.
    You should be able to rebuild your 231 with all the stock parts. Often, the crank is fine to reuse with only a minor polishing. Is your 231 block worn so much that it needs a rebore? Does your engine, in fact, have the deep dished low compression pistons used with the turbo, or are they the shallow dish pistons? The 231 shares the same bore diameter with other Buick engines, but using V8 pistons would require machining to account for the offset of the split-pin 231 journal. There was also a 3.0 liter Buick V6 thay shares the same bore, and has the split-pin crank, only shorter stroke. I have heard of using these pistons in a 3.8, but I don't know the pin height. You should be able to just rebuild your 231 with the same parts as any mid-80s Buick 231 out of a naturally asperated Regal. For your purposes, your not trying to build a high-performance engine.
    As far as the flywheel, what did the "parts" engine/chassis have you are trying to use? You could have the machinist re-balance your 225 flywheel, but the Jeep odd-fire part was very heavy (and designed to dampen the odd-fire pulses) compared to the passenger car 231 flywheel, so it is not an ideal candidate, this is all assuming you have a manual transmission. Many Jeepsters came with a TH400 automatic, simpifying the flywheel delema.
    Lots of questions!
    Dauntless1971 likes this.
  4. Apr 25, 2020

    Lockman My " Rosie" 2020 Sponsor 2019 Sponsor

    White City, NY 14617
    Dec 4, 2018
    To my knowledge , there were not any NA 231's after 1983 ? Try this site , but be careful.... these guy's are Purist's . :
    Turbo Buick Forum | Buick Grand National | T-Type | Turbo T
    Here's some info from an expert :

    " On vs Off center
    Stage 1 vs Stage 2

    Lots of confusion here with a lot of this so I am going make a post about the differences.

    First off any Stage block was a Buick Motorsports block built for racing and the afternarket they were not put in any production vehicles and there are MANY variations of these blocks which makes it really confusing to follow.

    Stage 1 vs Stage 2

    Stage 1 and Stage 2 blocks are the SAME blocks just machined differently with different main caps. Stage 1 blocks came with 2 both mains 8 head bolts and oil pump pick up in the stock location. There are said to suffer from core shift more commonly than S2 blocks and the theory is that these blocks were rejected S2 castings sold as aftermarket replacements. S1 blocks can be machined for S2 four bolt main caps and easily drilled for 14 head bolts. I've owned a few S1 over the years and some of them can be nice blocks but I have also heard of people having a lot of issues with them.

    The S2 off center blocks come with 4 bolt main caps and 14 bolt heads and the oil pump pick up is in the front of the block and not in the middle like a stock motor due to the four bolt main caps.

    BMS made both a 3.8 and a 4.1 S1 and S2 blocks in off-center. These blocks are very desirable for turbo buick owners because they literally drop in with everything bolting up with minimal fabrication. They are also very hard to find in decent shape. A lot of them have been run really hard, damaged then repaired and some are just plain used up. They produced on center blocks in much greater quantity up through the late 90's while the off centers were last produced in the 80's. I only bought the 4.1 off center last year because in 30+ years of racing these cars I never owned a nice one and the one I bought is mint.

    Off vs On Center.
    The V6 in a turbobuick has one bank of cylinder off set 1/8 of an inch making it "off center" of the crank pin. The connecting rod is also offset to compensate for this to one side. To make an on-center block work you need an on center intake since one side of the offcenter is offset and you have to mill the front covers or shim the crank pulley to make them fit with the factory accessories and align correctly.

    On-Center: At some point in the mid 80's Buick Motorsport decided to center the one bank of cylinders making an "on-center" block since they were being used heavily in racing. I believe it is the passenger side that is offset on an off center. I dont believe there was ever a 3.8 bore on-center block and all on center blocks were Stage 2. That's not to say there isnt one out there somewhere as a freak Buick experiment."
    Last edited: Apr 26, 2020
  5. Apr 26, 2020

    Lockman My " Rosie" 2020 Sponsor 2019 Sponsor

    White City, NY 14617
    Dec 4, 2018
    This may help identify the Block ? :

    Attached Files:

  6. Apr 27, 2020

    timgr Jeepin' Nerd 2020 Sponsor 2019 Sponsor

    Medford Mass USA
    Aug 10, 2003
    What's the bore measurement now?

    Assuming these blocks are conventional gray iron USA blocks. This allows two rebuilds typically, one at 30 and a second at 60. If you have any doubts, have the block sonic checked and measure the wall thickness. That said, if the block has never been bored, you are throwing away some material by skipping 30 and going direct to 60. Your machinist should be up on this, but maybe things are different on an island. Ft. Myers isn't very far ... maybe check with local car clubs or online forums for other places to take it?

    I go to RockAuto and find Sealed Power 30-over pistons for both a '77 odd-fire 231 Skylark and an '82 even-fire Regal, both normally aspirated and less than $20 each. If you want compression higher than what the factory provided, you may need to get custom pistons - not difficult, but more expensive. There may be high-compression off-the-shelf pistons available from someplace like TA Performance.
    Last edited: Apr 27, 2020
  7. May 1, 2020

    fhoehle Sponsor

    Harford Township, PA
    Apr 11, 2012
    Call TA performance, they will have the pistons you want, most likely. Very knowledgeable and very helpful. I really enjoyed dealing with them for a number of my V6 parts. I bought Silvolite pistons for my 225 from Summit though, I think. They are .030 over, found in pretty much any speed shop. I hear 231 has many more choices in pistons but TA will have the lowdown. If it's a trail and driver Jeep, don't get crazy about compression, nobody wants to buy premium all the time. Lol
    Last edited: May 1, 2020

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