Piston to Valve Clearance-Solid Lifters
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  1. #1
    1000+ Posts pgti6's Avatar
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    Default Piston to Valve Clearance-Solid Lifters

    Can anyone confirm the accepted piston to valve clearance when solid lifters are used in an XU9J4 engine?

    I understand that hydraulics need around 0.80" inlet & 0.100" exhaust clearance, but mechanical lifters can run closer tolerances as valve float is eliminated. Would it be advisable to use 0.060" inlet & 0.080" exhaust as a minimum?

    Thanks

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  2. #2
    1000+ Posts alan moore's Avatar
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    Actually valve float is not eliminated,( ie the springs may still not control the valve movement) and I would still want to run 80 thou min inlet and exhaust. It might be nice to know how far you can move the cams before encroaching upon this measurement.

    As soon as you fit adjustable pulleys on you will want to adjust them to see if you can get better characteristics out of the motor, so it would be nice to know how far you can move them before bad things happen.
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  3. #3
    Fellow Frogger! racing405's Avatar
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    I have just travelled this path too. I would definitely not go less clearance than recommended, in fact, I have set mine up with a little over the recommended 0.20mm = about 8 thou or 0.008". I have actually set mine up with 0.010" (ten thou) which works out to be more or less 0.25mm. I do not know how rapidly the valve clearance will change, but I would prefer to have a little extra room to start out with.

    I actually have a spare set of solid lifters if you are looking for a set, they are Cat Cams CC003s.

    In the absence of better advice, I would not go under the 0.20mm recommendation for valve clearance when setting up your solid lifters.

    Cheers.

  4. #4
    1000+ Posts pgti6's Avatar
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    Thanks both Alan & Ben for your replies.

    Alan I have measured the piston to valve clearance at TDC when I built the engine & have adjustable cam gears which allowed me to swing the cam timing around when the engine was tuned. I know I'm entering the 'danger zone' and cannot advance the inlet cam any further.

    Since making the decision to use mechanical lifters, it will also require new cams as the grinds are different to those used with the std hydraulics, so the info I was after is what the minimum piston to valve clearance at TDC that I can safely use. I realise that the distance approx. 6 degrees either side of TDC will be even less as the piston is momentarily stationary while the valves are still opening/closing.

    Ben I think you're referring to 'lash'? This info should be supplied by the cam manufacturer as 0.008", 0.010" or 0.012", etc clearance with a separate figure for inlet and a usually wider one for exhaust.

    Thanks for the offer of the Cat Cams lifters, but I already have a set of Arrow titanium ones.

    Jeff
    405 Mi16 2.2 litre race car up for sale soon. For details contact me on 0438 106 430.

    Lap times- Sandown 1 27.9
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    Previous Frenchies-
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  5. #5
    Fellow Frogger! racing405's Avatar
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    Your'e quite right, I am referring to valve to lifter clearance or "lash". Upon reading your post a second time, your question and the figures you included makes a lot more sense.

    With the Wossner pistons I am putting in the new engine, the valve to piston clearance will bottom out at over 0.100" at standard timing as the valve pockets in the pistons are slightly larger and deeper than the originals. Significant measurement for those pistons will be piston dome to head clarance on the standard head gasket. My block and liners have not been decked.

    Cheers.

  6. #6
    1000+ Posts PeterT's Avatar
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    I still wouldn't go under 0.080"/0.100" even with solids @ TDC, this figure will reduce by approx. 0.010" at the closest point either side of TDC. So in reality, you're talking 0.070"/0.090". I "think" that's ok for that size valve/spring mass. Remember that the 0.080" figure is generally taken as acceptable for large V8 valves.

    In regards to valve clearance, 0.010" is fine for the inlet, but the exhaust should not be less than 0.012" otherwise you'll start riding valves and burning them out.

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  7. #7
    1000+ Posts pgti6's Avatar
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    Thanks Peter, that confirms Alan's view too. I'll have the piston valve reliefs/head gasket thickness adjusted (to maintain or increase the CR) to suit the new cams.

    Jeff
    405 Mi16 2.2 litre race car up for sale soon. For details contact me on 0438 106 430.

    Lap times- Sandown 1 27.9
    Phillip Island 1 53.8

    Previous Frenchies-
    1988 205 Gti
    1998 306 GTi6
    1997 306 N5 sedan
    1996 306 N3 XT hatch
    1976 Renault R16TS manual in Avocado
    1976 Renault R16TS manual in Trak Yellow
    1975 Renault 5 Guernsey, Channel Islands
    1972 Renault 4 Guernsey, Channel Islands

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