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  1. #1

    Join Date
    Mar 2011
    New Zealand

    How Much Damage ?

    i've been tracking downa lack of acceleration and reduction in top end on my 98 XPL 951.

    Found the issue of cracked exhaust near the manifold. I've pulled the plugs and the RAVE valves to get a look at the pistons.

    Piston crowns are really clean, as are the plugs and the RAVE s so presuming steam has been washing the carbon and the oil off. Pistons sides from what i can see look pretty good.

    Compression is down to 120 psi (was 135psi after a full rebuild two seasons ago). Probably put 7 tanks of gas through it while it was leaking.

    Question is - what other damage could the water/steam have done and at what compression do you decide to do the top end.

    I've never seen 150 psi even straight after new pistons and a rebore.



  2. #2

    Join Date
    May 2007
    A tell tale sign of a water entering the cylinders from the exhaust manifold is the pisser doesn't flow continuously and is hotter than usual. I have had a head gasket leak for a few weeks and the top of the piston was completely gone about 40 mm around the circumference of the piston.The rings where still in place just floating by themselves until the rings rejoined the piston. You could place your little finger between the piston and the ring it was that big.
    When you pull the cylinders off have a look at the bottom end for any discoloring of the rods and make sure the crank bearings are smooth and quiet.

    I always use OEM gaskets now for peace of mind and I have never had problems with them.Some aftermarket head gaskets just dont provide a lasting seal.

    135 psi is about right for a stock 951 to blow, besides 951s dont need a lot of compression to give good torque .

    Compression usually comes up to max after 5-10 hrs .

    Get the exhaust fixed and use a new OEM Manifold/Exhaust gasket and bolt it on without the carbys on as you can get an even spread of torque on the bolts and Nut under the pipe.

  3. #3
    dan87951's Avatar
    Join Date
    Apr 2010
    Lansing, MI
    Over time the exhaust bolts become loose so its good to double check torque and use thread lock on them. There is a lot of vibration with these engines.

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