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Thread: flywheel bolts maybe too long

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    flywheel bolts maybe too long

    My engine is now completely rebuilt but I haven't mounted the flywheel yet. I used the uprated rear oil seal conversion sold by bpnw (the one that doesn't require grinding the scoll) but I fear I'm going to have a problem with the flywheel bolts being too long. The new seal has an extruded ring around the shaft that the old seal didn't have and after measuring the bolts it seems they will hit that ring.
    I could maybe just add a washer to the old bolts to get the clearance but one disappeared leaving me with only three and are no longer available. The new bolts being sold are the same 7/8" length measured from under the head and no washers are to be used with them. Since these bolts are kind of a special breed, I'm stuck in a dilemma as to how to proceed.
    So my question is, has anyone used the modified seal and experienced this bolt issue? if so, how did you work around it? What bolts did you use etc..?

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    Re: flywheel bolts maybe too long

    I'd just grind away the excess length. Go slow, and maybe add a little water mist from time to time, so you don't get the remainder of the bolt hot enough to change the temper.
    Randall
    56 TR3 TS13571L once and future daily driver
    71 Stag LE1473L waiting engine rebuild
    71-72-73 Stag LE2013LBW waiting OD gearbox rebuild

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    Re: flywheel bolts maybe too long

    I have done this three times. The bolts are absolutely too long, it will destroy the seal immediately. I just grind the end off the bolt in the bench grinder. I dry fit the flywheel to the crank before i install the crank in the engine to check but generally, grind off a full thread. You can carefully shine a flashlight into the gap and see if it touches.

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    Re: flywheel bolts maybe too long

    I have found that the UNF Bolts are available at Lowes and Ace Hardware in the special bolt section. Take a bolt with you to check the thread pitch and length.

    Not at home so I can't check the size.

    David

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    Re: flywheel bolts maybe too long

    I would be very cautious about using a regular fine thread bolt in this application regardless of the strength.

    Look closely at the bolts you have. The correct flywheel bolts have a tapered portion on the body just under the head. The purpose of this taper is to securely position the flywheel due to the interference between the bolt and hole in the flywheel. It is essentially a type of locking mechanism.

    A regular fine thread bolt does not have this taper. There will be clearance between the body of the bolt and the hole in the flywheel. The flywheel will then be held in position only due to the dowel pin and friction due to the clamp load of the bolt.

    That might be sufficient to keep things together but why take a chance.

    If you want to confirm this just put one of the old bolts into a hole in the flywheel and then put a regular bolt of the same thread into the next hole. Try to move the correct bolt sideways in the hole when pushing down on it lightly. Do the same with the regular bolt.

    There is one trick I use when cutting or grinding a thread fastener shorter. I install a nut and turn it beyond the place where I will cut off or grind. Then I can turn the nut off to remove any burr or distortion of the threads at the "new" end of the fastener. Makes it a lot easier to start the new threads.

    I also agree with the advice to grind slowly and control the heat going into the bolt with some water. Those are heat treated bolts. Overheating can affect the strength.

    Rusty

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    Re: flywheel bolts maybe too long

    More great info from this site. I think all the bolts I used were in the flywheel when I took the motor down but who knows what the POs did with it. I will check my bolts when I get home.

    Thanks Rusty

    David

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    Re: flywheel bolts maybe too long

    I see what you are referring to. The bolt does not show up in the hardware catalog as a standard type bolt.

    RimmerBros have the later bolt in stock. The old number is 102065 according to my parts book. RimmerBros suggest using 138527 instead. Self locking. You would probable still have to cut it down.

    David

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    Re: flywheel bolts maybe too long

    Hi David,

    I expect that whatever you buy you will need to shorten them to prevent interference with the seal.

    My friend used the high tech ARP bolts ($8.19@ vs. $3.49@ at Moss) in his TR4A. I could never figure out what advantage they offered especially in a stock engine.

    The clamp load between the flywheel and crank hub is determined by the torque you apply, not the strength of the bolt. And remember that all bolts of the same size stretch at the same rate based on load. The difference is the amount of stretch the bolt can withstand before it fails.

    I agree that the higher strength bolt will withstand more tightening torque. The limitation in this case is what the threads in the crank hub can withstand. So unless you are doing something to increase the capability of the threads in the crank, you cannot apply more load.

    In a properly designed and assemble joint there is no relative motion between the parts. So the bolts are never loaded in shear, only tension. Unless of course you are designing a shear bolt application which is a whole different set of problems!

    Rusty

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    Re: flywheel bolts maybe too long

    When rebuilding all my engines I always go back together with the ARP products where possible.
    More expensive- no doubt. If you've ever seen what happens to a flywheel at 6K you know what I'm talking about.
    Harry

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    Re: flywheel bolts maybe too long

    Thanks Fellas, I really appreciate the input!
    Since I'm only anticipating having to do this once with this engine, I think I'll forego cheap on this phase, play it safe and use the ARP bolts. The torque specs I have say 42 to 46 Lbs for flywheel to crankshaft.. whadya think..sound about right?

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    Re: flywheel bolts maybe too long

    I don't remember; but believe ARP will give you the torque for the bolts with
    the package.
    Harry

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    Re: flywheel bolts maybe too long

    My suggestion is that unless ARP is willing to guarantee that the threads in the crank flange will take a higher load you need to use the factory torque spec.

    The result is that you have the same clamp load with ARP bolts as the factory bolts.

    One advantage of the ARP bolts is that if things do become loose it takes more load to shear them. So you might be able to keep the flywheel in place long enough to get things slowed down.

    Remember that once any bolt is loose there is no clamp load nor any resistance to the bolt backing out.

    Rusty

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    Re: flywheel bolts maybe too long

    I'm a bit confused and worried now. My TR4 motor has Christian Marx rear seal with the original flywheel bolts.
    I'm going to start it next week, should I have shortened the bolts?
    The engine turns freely using a screwdriver on the fan extension.

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    Re: flywheel bolts maybe too long

    Quote Originally Posted by jimstr4 View Post
    I'm a bit confused and worried now. My TR4 motor has Christian Marx rear seal with the original flywheel bolts.
    I'm going to start it next week, should I have shortened the bolts?
    The engine turns freely using a screwdriver on the fan extension.
    There is enough manufacturing tolerance involved that you may be OK, especially if you installed the lock tabs as original. But turning freely now is no guarantee that the bolts aren't sticking out enough to rub on and damage the Viton seal, especially when the crank gets shoved forward by the clutch.

    And if that part of the instructions was ignored, I would be wondering what other parts got missed as well.

    Randall
    56 TR3 TS13571L once and future daily driver
    71 Stag LE1473L waiting engine rebuild
    71-72-73 Stag LE2013LBW waiting OD gearbox rebuild

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    Re: flywheel bolts maybe too long

    I will be taking the gearbox out and shortening the bolts by about 1\8". Great that I read this post and thankyou to all for the information.

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    Re: flywheel bolts maybe too long

    Unforetunately I had the old instructions which made no mention of the seal sticking out and having to shorten the bolts.

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