Fixing what’s not broke…

Discussion in 'Mech Tech' started by mcswiggs, Nov 11, 2022.

  1. even with valves you’ll lap a ridge into the new valve . Depends when cutting seats if you use a stone or cutter style as to how good a job it makes . My biggest fault being an engineer is I get a bit too anal about some things and I have to re grind the old valves to do the initial lapping then just the final tickle with the new valves .
     
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  2. mcswiggs

    mcswiggs Supporter

    Thanks @lhu1281 and @77 Westy.

    By lapping I meant putting some grinding paste on the end of the cylinder and giving it a bit of a twirl on the head, rather than anything more technical. Sounds like this is worth doing…?
     
  3. Zed

    Zed Gradually getting grumpier

    Sounds like a way of introducing grinding paste for no good reason... except maybe a quick whizz might show up any high spots.
    To be extreme, imagine you had a match head sized high spot on the cylinder. You grind and what happens? If you do complete circles you grind a trough into the head but you still have you high blob on the hard steel.
     
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  4. mcswiggs

    mcswiggs Supporter

    Beautiful way of describing it @Zed . Hadn’t really thought the difference in hardness in the two surfaces - so I think the grinding paste will stay in the pot. Cheers!
     
    Last edited: Mar 26, 2023
  5. Zed

    Zed Gradually getting grumpier

    Grinding valves is different because they do turn in operation. But the same applies. If you have a high spot on one, turning it repeatedly on the other might get rid. I had a valve seat in a new head where you could see the cutter had chattered. It was minuscule you you could see it. My god that took hours. I don't think you make much impression or do much harm with grinding paste but it can show up oddities much like engineers blue. Really, it's the machining. If everything is parallel it'll be fine.

    Just my opinion of course.
     
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  6. mcswiggs

    mcswiggs Supporter

    Uh oh - problem time.

    So, my mate from Munich has turned up with a stash of cylinder base shims from CSP so I’ve been able to restart the rebuild. But I’ve hit a problem.

    I assembled No 1 piston/cylinder and popped it on the engine with the new seal just to double check the deck height. What I’m getting is a miss-match on the deck height measurement from one side of the piston to the other (i.e. measuring along the line of the pin). There’s a discrepancy of about 0.5mm, which is a lot!

    So, I’ve checked the geometry of the new pistons and cylinders and they are all good within 0.01mm. And I’ve put a steel rule over the faces of the cylinder seats on the case and tried to get a feeler gauge underneath - the 0.02mm one is the smallest one I’ve got and that’s too big, so that’s all good.

    So then I used two pins to mount the piston on the con rod - with the ends of the pins sticking out I can measure the alignment of the piston to the cylinder seat on the case - and there’s a big fat 0.5mm difference at the two extremities - have a look at the photos to see what I mean….

    39ADA65F-CE83-41F7-B478-B54F2568D561.jpeg 55FB373F-1F0F-422C-93C1-C70583C86A08.jpeg

    Seems to me that the con rod is bent - are there any other realistic possibilities?

    This is particularly annoying because the machine shop was supposed to have checked and straightened all the rods.

    I can’t see why I can’t whip out the con rod without having to split the case again - could anyone put me right if I’ve got this wrong?

    Just going to check the rest of the rods now…. Cheers…
     
  7. Zed

    Zed Gradually getting grumpier

    That's... unfortunate.
    Yes you can whip out conrods without splitting the case.
     
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  8. 77 Westy

    77 Westy Supporter

    Turn the rod 180deg and check the pin again and measure the pin height in the piston one side to the other.

    If you need a set of rods (with the oil spray mod) I happen to have them on the shelf and I’ll be coming to the UK in a couple of weeks. :D
     
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  9. mcswiggs

    mcswiggs Supporter

    Good idea! Just to confirm, you mean undo and remove the con rod and pop it back in effectively upside down and repeat the measurement.
    Thanks for the offer of con rods very much appreciated - I’m hoping that after I’ve had words with the machine shop I won’t need to take you up on it!
     
  10. 77 Westy

    77 Westy Supporter

    Yes, it will indicate if the rod is bent if the pin 'gap' moves from one side to the other.
     
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  11. mcswiggs

    mcswiggs Supporter

    Got it thanks. Running out of time now so will be Wednesday before I can carry on.
     
  12. mcswiggs

    mcswiggs Supporter

    Well that confirms it, with the rod on the other way round the gap shifts to the other end with it - bent rod. There's about 0.2mm different in length from the pin bearing to the big end bearing from one sideto the other. 640AE3FF-2F84-4FF5-B753-8B47BC4E2396.jpeg
    I’ve checked No2 cylinder and that’s not as bad but not good enough.
    I was under the impression (from reading Wilson) that it’s possible to straighten rods, is that the case?
     
    Last edited: Mar 29, 2023
  13. 77 Westy

    77 Westy Supporter

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  14. mcswiggs

    mcswiggs Supporter

    Thanks Geoff. Spoke to the workshop who did the work on the rods and crank - the guy can't understand how the rods can be out but he hasn't got the means to straighten them so not really worth the two hour round trip to prove a point.

    I've contacted Reconditioning Experts and am expecting an automated quote (why can't they just give a phone number like firms used to??) and see what they say. There are one or two others on the web who offer a straightening service so I'll scout around a bit. Cheers for your advice once more.
     
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  15. you’d be able to tell if it’s bent fairly simply with a straight edge . They may have just reamed the small ends on the wonk. If they are bent they just use a arbor or hydraulic press to straighten then new small ends and ream /bore square
     
    Last edited: Mar 29, 2023
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  16. mcswiggs

    mcswiggs Supporter

    Steve - yes you’re right. I’ve measured every which way and I don’t think the rod is bent, it’s the bush that’s on the cock. Another rod is straight and ok, another half as much cocked and the last straight but too long. The guy from the machine shop is avoiding me but I’ll pay him a visit tomorrow!
     
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  17. Take Big Barry with you. He'll soon see sense :thumbsup:

    Little ends reamed on the cock far more likely than bent rods, I'd think.
     
    Last edited: Mar 30, 2023
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  18. Chrisd

    Chrisd Supporter

    If you need help or moral support just shout.
     
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  19. Once he sees Big Geoff's tattoos, he'll soon see the error of his ways :eek:
     
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  20. Well that’s bad but not the end of the world . One of the reasons I do everything myself . These days they would be CNC milled within microns of each other
     
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