807 pistons and rods
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Thread: 807 pistons and rods

  1. #1
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    Default 807 pistons and rods

    I know this subject have been discussed here before. But I have a question that I can't say I have found the answer to. I apologize if some of my words are not correct.

    I have a set of rods from a 807-10 engine. These has the piston pin pressed in the small end of the rod. I bought a set of new pistons. These has a floating pin and if I don't remember wrong the pin was 1mm bigger in diameter. I was in contact with an company to get them to make a bigger hole in the rod and fit piston pin bushes. They could make me a set of new bushes. Do anybody know what the thickness of these bushes originally was? And will the rods handle the bigger hole in them?

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    1000+ Posts geckoeng's Avatar
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    I would not recommend boring the small end, they are not that strong in standard form.

    But the pistons supplied are incorrect if the pin is bigger. Are they pistons from another engine ???

    Ray
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    COL
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    The pistons that you are after are for the R17TL and what you have are for the R17TS and also the R12G not sure of the engine designations for the R17TS and R12G.
    Regards Col

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    Yes, it is correct that my engine is a 17TL and the pistons are for 17TS/12G. I bought a 1596 kit from Mecaparts with liners and cast pistons. Had a hope of using the rods I have but I maybe have to get hold of a set of correct rods.

    I saw someone in here did this modification, but without the bushes. But that is propably a bad solution?

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    1000+ Posts Frans's Avatar
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    Quote Originally Posted by R8RX View Post
    I saw someone in here did this modification, but without the bushes. But that is propably a bad solution?
    Maybe this is me. I have many times and in many competition engines had the small end reamed out to accept the piston pin on a floating size. That means you don't need to do the extra big size to accommodate a bush. All needed is a oil hole at the top of the rod that is reamed a little to form a type of countersink like hole for lubrication. The piston pin becomes floating so I hope you have circlips or teflon stops on the piston to keep the pin from sliding against the sleeve.

    It has never failed me yet but maybe others on AF had problems with this method??

    Regards, Frans.
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    Quote Originally Posted by Frans View Post
    Maybe this is me. I have many times and in many competition engines had the small end reamed out to accept the piston pin on a floating size. That means you don't need to do the extra big size to accommodate a bush. All needed is a oil hole at the top of the rod that is reamed a little to form a type of countersink like hole for lubrication. The piston pin becomes floating so I hope you have circlips or teflon stops on the piston to keep the pin from sliding against the sleeve.

    It has never failed me yet but maybe others on AF had problems with this method??

    Regards, Frans.
    Thank you for your answer Frans. So no problem with the bigger hole? The engine is going to be used as a race engine. But is only "medium" tuned, not a full race engine. Do you make the hole at exactly the pin size or just above? Circlips for each piston followed in the kit. What do you use to make the hole bigger?

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    1000+ Posts Frans's Avatar
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    The bigger hole in this case will only be increased by 1 mm. I a bush is made the hole will be increased by about 2.5 mm. That could be to big for the rod size. I am not familiar with those rods but I think Col and Ray can confirm and maybe agree with a 1 mm increase.

    I send the rods in to an engineering shop to have it done in a machine I don't think I will do it by myself because the dimensions are too critical. I'm not sure what the oversize clearance of the hole will be but testing it with a bit of oil should give you the same feel when you move it sideways over the pin. It should move freely but with no apparent looseness or play.

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    Quote Originally Posted by Frans View Post
    The bigger hole in this case will only be increased by 1 mm. I a bush is made the hole will be increased by about 2.5 mm. That could be to big for the rod size. I am not familiar with those rods but I think Col and Ray can confirm and maybe agree with a 1 mm increase.

    I send the rods in to an engineering shop to have it done in a machine I don't think I will do it by myself because the dimensions are too critical. I'm not sure what the oversize clearance of the hole will be but testing it with a bit of oil should give you the same feel when you move it sideways over the pin. It should move freely but with no apparent looseness or play.

    Frans.
    Thank you, I have a dialog with a company regarding other things i need to get machined, so as you say, it is better if they can do it.

    What diameter do the oil hole on the top of the rod need to be?

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    1000+ Posts Frans's Avatar
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    I've always made them 2.5mm and then countersink it with bigger drill about 6 or 7 mm to create a funnel assisting the oil to collect on top and flow into the rod and pin.

    Frans.
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    I know they will not be easy to find, but my first choice would be to find a
    set of R12/17 gordini connecting rods. No risk of failure as they are much sturdier
    than the TL rods and an exact fit without any modifications.

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    Quote Originally Posted by Frans View Post
    I've always made them 2.5mm and then countersink it with bigger drill about 6 or 7 mm to create a funnel assisting the oil to collect on top and flow into the rod and pin.

    Frans.
    Thank you very much

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    Quote Originally Posted by Steve K View Post
    I know they will not be easy to find, but my first choice would be to find a
    set of R12/17 gordini connecting rods. No risk of failure as they are much sturdier
    than the TL rods and an exact fit without any modifications.
    I am fully aware of this. But as you say availability could be an issue. But I will see what I can find

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    1000+ Posts geckoeng's Avatar
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    What is the diameter of your piston pin on the new pistons ??

    Ray
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    If I remember correctly they are 21mm in diameter. Can measure both new and old pin tomorrow night.

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    I think I definitely need to measure the pins again after reading a thread about different rods and pin sizes on these engines. Most of the pins are 21mm, but only the 12G/17TS rods have a floating pin.

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    Pretty sure eBay had the rods you require listed new including arp bolts for under $400 delivered. Don’t know the quality. Has anybody used these?

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    1000+ Posts alan moore's Avatar
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    I have set of the MaxSpeeding R12G rods I will be fitting in a few weeks. They were $365 or so landed, and as best as I can measure are correct with good tolerances. I know a number of people that have these in Japanese turbo machines running significant boost without problem over some years. Not a lot more expensive than getting your original rods sized and having the small ends machined out.
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    Quote Originally Posted by alan moore View Post
    I have set of the MaxSpeeding R12G rods I will be fitting in a few weeks. They were $365 or so landed, and as best as I can measure are correct with good tolerances. I know a number of people that have these in Japanese turbo machines running significant boost without problem over some years. Not a lot more expensive than getting your original rods sized and having the small ends machined out.
    https://www.maxpeedingrods.com/Renau...am-Conrod.html

    With 7% discount to.

    They look great as well.
    Regards Col

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    Sounds like a good endorsement Alan. I’d been thinking about buying a set for a while. Maybe I should while they’re available.

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    Managed to measure the pins before work. Old pin 20mm, new pin 21mm.

    Yes, those rods seems to be an option I need to consider. The price I got for making new bushes and to fit these was about 500usd. So not much to think about really.

    Haven't got the cost for just making the hole in the rod bigger.

  21. #21
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    Quote Originally Posted by alan moore View Post
    I have set of the MaxSpeeding R12G rods I will be fitting in a few weeks. They were $365 or so landed, and as best as I can measure are correct with good tolerances. I know a number of people that have these in Japanese turbo machines running significant boost without problem over some years. Not a lot more expensive than getting your original rods sized and having the small ends machined out.
    For NOT750?
    JohnW

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    Quote Originally Posted by JohnW View Post
    For NOT750?
    Yes, with a new camshaft idea, and fuel injection eventually.
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    I'm as ever interested in the camshaft matter!

    Good luck with it and see you in Inverell, if not en route in Rob's R10!
    JohnW

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