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Thread: One for Stewwie.

  1. #1

    One for Stewwie.

    Hi Stew, your mailbox is full so I'll ask a question here:

    The SR has developed a nasty deep vibration so I'm going to rebuild the bottom end.
    Who do you you use for crank rebuilds/balancing and do you use the Carrillo rods or the ones Carl gets made?

    davy
    Adding power makes you faster in the straights.... adding lightness makes you faster everywhere: Colin Chapman

    There is a quintessential elegance to riding a single cylinder machine: OCR

  2. #2
    Yes, might be worthwhile for sure...check the end of the crank for movement by hand...might be the mains.

    But I guess if you use the excuse of pulling it down to replace things...I usually do......then a new rod and big end might be in order.

    I find that without re-balancing the Carrillo can result in unwanted vibration...I have a couple and they all do the same thing...never bothered to re-balance the crank...although maybe I should have.

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    It'd be a pain for you to replace everything and not be happy due to a different sort of vibe...

    I'd been told 60% as a balance figure (by a crank guy in Sydney) but like all things it probably works best over a 'certain' RPM range which may not suit you in the end (heh, heh...bit of a pun there.. ).

    You'll need to modify the oil scraper on the cases to fit the Carrillo big end clearance too.

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    If the ones Carl sells are lighter then that probably better...although a new standard one is pretty good too.

    For racing I'd life the standard rod to a season...that's purely my thinking on the matter...I've seen them fail at the little end after a few seasons of hard racing and it makes a big mess!

    For the road however...in a performance engine likely the brand new standard one is fine for a long time.

    I did use a guy here to do mine, but probably not anymore...maybe Serco in Brisbane...I use them for re-bores now too.

    Hope that mess assists...

    SR
    Last edited by stewross; 06-07-2017 at 07:51 AM.
    ...'Any unnecessary items on the bike, that it doesn't really need, shouldn't be there!'. (Café racers creed). SR..

  3. #3
    Thanks Stew.

    Not sure what the issue is for sure. Motor ran fine until today, backed off to take an S bend at about 140k, re-applied the power and this horrible deep vibration started.
    Ran it home 12k at 90kph no problem but it really gets bad again at around half throttle.
    Piston is good, no smoke with lots of power and the piston top and plug look perfect.
    Not a lot of things to make that sort of vibe so as it runs 17/40 gearing not a lot of revs being used so right now I'm discounting a piston problem especially as there is no noise to give it away so I'm thinking big end.
    Can't feel any main bearing movement at the flywheel end.
    Clutch feels fine and adjustment hasn't changed so probably not the drum come loose either.
    I didn't put this motor together so not sure what I'll find in there, all I know is it's got a 90mm piston and a Tighe 323 cam and I've added a full flow stainless exhaust and a VM38 with a long velocity stack.
    All mounting bolts are tight as a drum, sprockets secure and chain as new.

    davy
    Last edited by Old Cafe Racer; 06-07-2017 at 09:04 AM.
    Adding power makes you faster in the straights.... adding lightness makes you faster everywhere: Colin Chapman

    There is a quintessential elegance to riding a single cylinder machine: OCR

  4. #4
    Senior Member gcrank1's Avatar
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    With it full cold pull the spark plug so you dont have to fight any compression and pick whichever way you want to be able to rotate the engine. Roll it down to BDC and take a mechanics stethoscope to the lower end and roll it back and forth, if the bottom has gone you should be able to hear it as it takes up the clearance changing direction. Do the same at TDC; Ive found I hear it better at the BDC.
    A lighter clank can be the wrist pin so listen at about where it should be sitting on the jug when at BDC and TDC.
    '81 Yamaha SR500 Caff Racer
    '09 Suzuki TU250X 'The Silent Red Fellow'
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    In all things maintain your uprightness lest the road reach up and smite thee

  5. #5
    Quote Originally Posted by gcrank1 View Post
    With it full cold pull the spark plug so you dont have to fight any compression and pick whichever way you want to be able to rotate the engine. Roll it down to BDC and take a mechanics stethoscope to the lower end and roll it back and forth, if the bottom has gone you should be able to hear it as it takes up the clearance changing direction. Do the same at TDC; Ive found I hear it better at the BDC.
    A lighter clank can be the wrist pin so listen at about where it should be sitting on the jug when at BDC and TDC.
    No noise but there is definitely some lost motion at tdc when rocking the flywheel so time to strip it for a look.

    davy
    Adding power makes you faster in the straights.... adding lightness makes you faster everywhere: Colin Chapman

    There is a quintessential elegance to riding a single cylinder machine: OCR

  6. #6
    Ah well, you always wanted to know what was in there anyway...

    Ensure you clean out the dirt trap in the crank as well.

    SR
    ...'Any unnecessary items on the bike, that it doesn't really need, shouldn't be there!'. (Café racers creed). SR..

  7. #7
    Quote Originally Posted by stewross View Post
    Ah well, you always wanted to know what was in there anyway...

    Ensure you clean out the dirt trap in the crank as well.

    SR
    True Stew as a couple of things I saw on the outside gave me little confidence in the bloke who screwed this motor together for the previous owner.
    Just a pity it didn't last another week as I'm just about to reassemble my old Daytona motor and I don't want two motors in bits at the same time...
    Guess I'll just have to ride the 853 or the Mito to the Ashton on Sunday.
    Adding power makes you faster in the straights.... adding lightness makes you faster everywhere: Colin Chapman

    There is a quintessential elegance to riding a single cylinder machine: OCR

  8. #8

    Not the bottom end :)

    Well, every picture tells a story.

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    Adding power makes you faster in the straights.... adding lightness makes you faster everywhere: Colin Chapman

    There is a quintessential elegance to riding a single cylinder machine: OCR

  9. #9
    that's, umm, interesting!
    1978 SR500E 2U8

    Confused about your frame number?
    http://xt500.free.fr/technique/numerosr.html

  10. #10
    Guess this means I'm chasing a replacement cylinder now then.. any leads?

    davy
    Adding power makes you faster in the straights.... adding lightness makes you faster everywhere: Colin Chapman

    There is a quintessential elegance to riding a single cylinder machine: OCR

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