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Burning Oil….Glazed Bores?

Home Forums Main Forum Burning Oil….Glazed Bores?

This topic contains 4 replies, has 3 voices, and was last updated by  Tony Smith 3 months, 1 week ago.

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  • #5586

    Tony Smith
    Participant

    Hello Gents,

    Does anyone have any ideas on the following problem. I’ve pulled my R3 Mk1 down after 500 miles since a re-bore as it was burning oil (1/2 a litre in 300km) (and a centre cylinder barrel pillar bolt had stripped) and all I can see that might explain it is the bores look shiny to me. There is some hone marks still to be seen. Not that I’m that experienced but I did note that the original hone marks seemed quite fine/light, at least as compared to what I recall from the past.

    There are significant carbon deposits on the pistons/head. The RH cylinder would smoke a little after a down hill run. The only other thing noted was the RH exhaust guide was a little out of spec and there was possibly some oil dripping out that exhaust flange.

    The oil pump is NOS and appears to be returning fine, tank levels are normal so I wouldn’t think the sump would be overfilling. The crank case breathing couldn’t be a issue. So I can’t see what might be forcing oil up pass the rings. I used a Penrite oil 20W60 as a lot of people in Australia seems to be doing which has 1000 ppm of Zinc if I recall. I wasn’t overly gentle when running the bike in, I gave it some short bursts of heavy throttle soon after getting out of the driveway.

    I have measured up the pistons and bores now and there appears to be around 2 to 3 thou clearance which would take another horn but before doing that I was wondering if anyone had any ideas as to why this might have happened. Obviously I am reluctant to reassemble without understanding why this oil issue occurred in the first place.

    Regards Tony

  • #5587

    David Smith
    Participant

    Tony

    The bores at that mileage should show good cross hatched honing marks, excess oil in the combustion chamber will lead to glazing. From your description it sounds as though you may have diagnosed the problem on one cylinder, but check all the guides, a worn guide on one cylinder doesn’t affect the other two, measure the valve stems and guide bore, or get someone to do it for you. I presume the rings were fitted correctly and were decent quality, but to be on the safe side fit new ones after honing, and fit them dry, oil the piston skirt lightly and no lubricant of any type on the rings or bores, they will bed in much better. Have a look at the dowels between the head and barrels, make sure they are not sitting proud and holding the head off slightly and allowing oil to seep past the gasket into the bores. One other thing that is possible, if everything else checks out ok, has the bottom end been apart? If the shells are badly worn excessive oil can overwhelm the rings and get into the combustion chamber, I’ve seen a perfectly good head and barrels affected this way, but as I said check everything else out first.

    Dave

    • #5589

      Tony Smith
      Participant

      Thanks David & Keith for taking the time to reply, Re the exhaust guide intuitively I wouldn’t have thought a lot of oil would have been lost here, there was 8 thou movement in one axis (it was a little oval) when checking by hand with a run-out dial gauge. Yes I will check all guides and valve stems. I believe “current practice” is to fit valve seals to the inlets only although one could fit guides with seal grooves to the exhaust as well.

      The pistons were new Hepolites (NOS about 15 or 20 years old). The rings are what I call “standard”, just rectangular section, and the oil ring has the “spring” running behind the double lipped oil ring. I assembled the gaps 120 deg offset. But I will look into a new set as a safety.

      I will re-check the dowels, there was no oil leaks on the top end, at least from the outside. The head had a 0.010″ facing before assembly, and rightly or wrongly, I put 3-Bond on the “paper” head gasket. I checked head bolt tension 3 times and re-tightened and did the tappets in those early miles.

      The bottom end was reground with new shells, pressures are good, running 30 to 40 PSI when warmed up so I doubt if this is an issue.

      Keith, re the carburation, I have been having troubles I must admit. But not with float levels too high but too low. I fitted new stay-up floats but spent more than a day trying to adjust them (which one would think should be simple) and couldn’t get them above their minim range setting as per the Amal write-up. I will have another go before re-assembly. I had made up a small supply tank with a little bit of head and tried to do them with the bowels off and on. But on the last pull down the LH and  middle cylinders looked to be burning quite lean so more work to do. The following comments apply to those low float levels so may need to redo things if I get them raised.

      The carby “process” started with bad running (rich) at ideal and small openings. I didn’t run much large openings early but they seemed OK. I found the needles were up one notch and I put them in the middle and re-tuned the pilots plus ran some vacuum gauges to trip the slide heights and from an outside point of view the bikes now ran well. There were no detected “vacuum” leaks, and all jetting is per standard although there seems to be a number of cutaways quoted by AMAL, mine are 3.5.

      So I’m not sure why the engine seems to be running on the lean side other the float heights. I guess runs in the countryside would be mostly around 1/3 throttle so maybe the cutaways are a bit steep but I guess I must get the floats set higher first.

      Thanks again. There certainly plenty of fun to be had with triples that’s for sure.  I’d welcome any other suggestions you may have. Regards Tony

    • #5590

      Tony Smith
      Participant

      I should have said 30 or 40 PSI at Idle

  • #5588

    Keith berry
    Participant

    hi, Tony as well i would check the float heights, as i found on my t150t if they are too high,it washes the oil off the bores and leads it to burn oil, I adjusted mine over the winter and,it now runs fairly clean,this is backed up by my wing man on runs out lol

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