Long Rod 300 Build

Discussion in 'Small Block Tech' started by Duffey, Mar 6, 2018.

  1. Duffey

    Duffey Well-Known Member

    Well, I picked up another complete 300 so I find myself rich in parts and have decided that stroking to 349 will incur a large and unneeded cost given my application. I am using the stock crank with late 350 rods on my 300 build. Silv-O-Lite HC3156 are 3.953 bore and would end up .008 below deck at the blueprint height. Plus, the rods only need honed .005 to fit the pins and cr is around 9.5 with the dish.

    Obviously this is geared toward a more street friendly engine with minimal cost. In my mind the advantages are a better, lighter piston with a better spring pack; better rod ratio; and stronger rods.
    Cast 300 replacement pistons are $360 from Summit, and the pistons I chose are $150 for a set of 6.

    I have looked high and low for info regarding oiling mods for the SBB, and really only found drilling out the oil pickup passage and front cover. I read some great articles on BBBs, but what really carries over?

    Also, I realize bearing clearances are crucial. It looks like one of my cranks will only need a polish, so I'm assuming just picking up standard bearings will be the way to go? Or do you really need to get oversize bearings and grind the crank to proper clearance?

    The reman 350 rods are on their way, and my plan is to finish the oiling mods on both blocks before taking them to the shop. That way if the first one doesn't check out they can move right on to the second. Thanks for the help!
  2. alec296

    alec296 i need another buick

    You may be fine with stock size Bearings. And summit does have a .001 bearing. Lists as good for Buick and Pontiac.
  3. 300sbb_overkill

    300sbb_overkill WWG1WGA. MAGA

    Make sure you sonic test the block to make sure you can bore that much out of your block!

    Standard bore size on a sbb 300 is 3.750", you're talking about doing a .203" over bore to use those pistons!

    You might want to slow down with buying parts right now and focus on a bit more research before you dive in.

    If you're interested PM me, I could give you a few tips on what parts that will work for your 300 build.
  4. Duffey

    Duffey Well-Known Member

    Oh goodness, good catch! I was thinking 3.795! Well, maybe a long rod 349 will be what I end up with after all.
  5. Duffey

    Duffey Well-Known Member

    1751H to the rescue! Its a thousandth shorter, a .905 pin, AND its the correct diameter (3.800). I remember Chris had to bush his 350 rods on his 349 build, and I believe his pistons were press pin. I thought you couldn't press a pin into a bushing?
  6. philbquick

    philbquick Founders Club Member

    Wouldn't forged GN pistons work if you went with a .050 over bore?
  7. Jim Nichols

    Jim Nichols Well-Known Member

    It is not a normal bushing. Steel tube pressed interference fit to the rod. Rod end chamfered and tube ends pressed to chamfer. Basically a spacer instead of bushing. It was my idea, but I don't know his mechanics specs on the fit.
    8ad-f85 likes this.
  8. Duffey

    Duffey Well-Known Member

    The forged GNs would work but, you know, $$$.

    Oh ok Jim. It looks like I might be able to set up the pistons like normal floating pins and use Teflon button retainers for the pins, but I need to do some more reading. If the steel bushing works it seems like it would be a better way to go though.
  9. 8ad-f85

    8ad-f85 Well-Known Member

    I hope I haven't skimmed past something obvious...but 305 or 283 forged pistons?
    The similar diameter import offerings aren't cheap either.
  10. Jim Nichols

    Jim Nichols Well-Known Member

    I like the 305 pistons. I think there was a Buick V6 one also. Ford 2.3 SOHC is 3.78 bore. What compression height are you looking for?
    Last edited: Mar 7, 2018
  11. Duffey

    Duffey Well-Known Member

    1.458 is the room I have (300 crank with 350 rod), and I would like to maintain proper squish. I realize the Buick heads are an “open chamber” design but it definitely has quench pads (albeit small ones). Plus I remember reading something about excess clearance causing carbon buildup or something? The 1751H is nearly perfect except for the wrist pin situation. From a cost standpoint it may be cheaper to have the pistons honed for a larger wrist pin—come to think of it, could my old 300 pins be reused? After be checked out of course?
  12. Jim Nichols

    Jim Nichols Well-Known Member

    I think when you started your other thread there was a Buick 3.8 V6 piston that was close. I mentioned it instead of the Holden one. That pin is the same as the V8. Are you in Australia? The 305 with 1.54 pin height I looked at using modified 6.25 Chevy rods.
  13. Duffey

    Duffey Well-Known Member

    Nope, I’m in the US. The only other pistons I really looked into were another Holden piston and the Olds for the 349. If Silv-O-Lite could just set up the piston for the .9450 pins and include them with a set of 6+2 that would be really nice, but for some reason I doubt a company that large is going to cater to an individual request like that.

    Well, I just got off of the phone with one of their techs. He said they could supply a set of 8 with a larger pin, but they will not hone the pistons. He also strongly discouraged me from trying to hone the pistons and said that the steel bushing approach shouldn’t pose any problems.
    Last edited: Mar 7, 2018
  14. 300sbb_overkill

    300sbb_overkill WWG1WGA. MAGA

    Where did you find 6.250" sbc rods for 2" rod journals? As far as the longest sbc rod I could find was only 6.125" for a 2" rod journal size.

    What size wrist pin hole is in the Holden pistons? And do you have a link for those you can post?(thanks)

    If they are .927" then you would NOT want to hone that much out, would be better to bore or drill most of it, leave around .004" to hone to size.

    An 15/16"(.9375") drill would get you close to .940" that would only leave you with .0035"(you want around .001" slip fit in the piston) to hone out IF the drill doesn't cut oversize?

    OR you could get an 15/16" hand reamer to open up the hole to get it close enough to hone;


    If it IS a .927" hole, that should be close enough to hand ream it to 15/16" to have it honed to size. Shouldn't be to bad to hand ream that much with aluminum. Make sure to use some sort of thin oil when you ream them, cutting oil would be best but if you have WD-40 on hand that would work just fine.

    If the hole size is .927", then only .019" or .0095" per side would need to be removed, that small amount shouldn't effect the structural strength of the piston, very minimal at most.

    If in you want to go to the .945" pin size, get the 15/16" reamer AND a 24mm hand reamer as well;


    With the 2 hand reamers you can get the hole size within .001" to hone out. .945" = 24.003mm which would be .0011" under where the clearance would need to be, so very easily honed for the proper clearance.
  15. Duffey

    Duffey Well-Known Member

    So the pin for the piston is .905 and the rods should be .940 right? I would post a link but Summit doesn't list any of the info, so you have to search the part number in the Silv-O-Lite catalog.

    The tech wasn't worried about the structural integrity, so much as the difficulty in getting the proper clearance.
  16. 300sbb_overkill

    300sbb_overkill WWG1WGA. MAGA

    There is really no advantage to running a 1.88:1 rod ratio in a sbb 300 that will only see less than 6,000 RPM.

    If you were building an engine that would see 7,500 + RPM then the extra rod ratio could be helpful. The factory shorter ratio is a bit more low RPM friendly, gives a bit faster piston speed to help fill cylinder on the down stroke.
    8ad-f85 likes this.
  17. 300sbb_overkill

    300sbb_overkill WWG1WGA. MAGA

    In that case you'll need one more reamer, probably a 23.5mm would get you to where the 15/16" will work;


    Or you could get 3 or 4 metric reamers from the above listing that will be around .015" over what the size is and over what it is reamed too. In other words you want to go up in size as close to .015" increments as possible, with less being better.

    To convert mm to inch simply divide the millimeter number by 25.4 which is equal to 1". For example, 23.5mm / 25.4 = .92519"
  18. Jim Nichols

    Jim Nichols Well-Known Member

    Derek, There were a few about 4 years ago. Probably not available any more.
    300sbb_overkill likes this.
  19. Duffey

    Duffey Well-Known Member

    Yeah the rod ratio is a pretty minor benefit given how good the factory ratio is. I look as the benefits of my current plan primarily as increasing longevity--less rotating mass to batter bearings, thinner rings that will seal better/longer, more durable rods, less piston side loading, etc. Though, if I get the heads ported they could support 6500rpm, maybe more, but that really isn't planned. Who knows, even all these added up might still equate to a negligible increase in benefit.

    I wonder at what point the cost of reamers outweighs that of just getting the rods bushed? It seemed like reaming the pistons would be really straightforward but like I said the tech heavily advised against it, and that's when I was suggesting having a machine shop take care of it.

    The 340 I was going to get the crank from will require me pulling the whole engine, but maybe the effort and $400 of machine work will still be the way to go. My main reason for trying to avoid it was cost, but it with bushing rods, etc. anyway that gap is closing rather quickly...
    8ad-f85 likes this.
  20. 300sbb_overkill

    300sbb_overkill WWG1WGA. MAGA

    "the tech heavily advised against it"

    The tech heavily advised against HONING the wristpins that much larger, as I would heavily suggest NOT even attempting to do.

    Seeing how the hole is .905" you could probably drill to a closer size to just buy 1 reamer to get it there the rest of the way. I would NOT recommend trying to drill them out with a hand drill though! Would need to be done on at least a drill press clamped to an angle plate setup with a wristpin in a V-block and the hole indicated on center and then locked down to the table.

    Switching to the sbb cap screw rods will add around 150 + grams more weight per rod than what the 300 rods weigh, so whatever weight savings from the pistons you get, you're adding that much or more to the rods.

    If you get the heads ported for more RPM, the factory cast iron cap screw rods will handle as much HP as you can throw at them N/A as long as you don't spin them much more than 6,000 RPM. A set of the new sbb 350 Molnar rods would handle the RPM, not so much the factory ones though.

    There is no really "cheap" way around it unless you can find an off the shelf piston that would work with a set of nascar take out rods.Which would be very hard to do because of the small pin size most of them have. You might get lucky and find a set of 6.200'' rods that have the sbc .927" pin size in them to either increase the size or re-bush smaller.

    The price of those rods aren't the issue, they can be bought for pennies on the dollar of what they cost new, its the cost to make them fit on the crank. There are 2 different sizes they come in, for either a 1.850" rod journal or a 1.889" rod journal. These will handle as high as 10,000 RPM so rod strength with these are WAY better than any factory rods you can buy, even with them being used!

    So you would have a plus or minus .070" with the 1.850" or plus or minus .050" with the 1.889" size by adding or subtracting half of the extra or removed stroke.(with the 1.850" rods you can gain or remove as much as .140" stroke and with the 1.889" you can gain or remove as much as .100" of stroke) Half of the stroke because for example the .140" extra or less would be .070" at TDC and an extra or less .070" @ BDC giving an additional .140" of total additional or removed stroke.

    It doesn't even need to be the full amount, you can reduce or add anywhere up to the .140" or .100" amount if that helps you find an off the shelf piston that will work. Just keep in mind that you will only move the piston up or down half of the added or removed stroke.
    Last edited: Mar 7, 2018
    Harlockssx likes this.

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