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  • #1

    951 exhaust bolts loose

    My '98 GTX has a 14 month old sbt engine in it that has run great, until now. It suddenly (over about 2 or 3 hours of use) started really bogging at low speeds, but then would hold a strong high rpm range. So I thought maybe plugs are fouled, so I changed them. It ran better, but something wasn't right. So this time when I got the seat off I looked carefully and noticed the loose exhaust bolts. The middle top one was actually out. I thought I followed all directions during reassembly, I thought I even rechecked them after a couple hours. The ski has about 15 hours on the new short block. I assume this isn't as easy as putting the bolt back in and re-torquing the bolts. My main concern is could any damage have been done to the engine?
    Thanks!
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  • #2
    Re: 951 exhaust bolts loose

    Which exhaust bolts are you talking about?
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    • #3
      Re: 951 exhaust bolts loose

      The bolts that hold the tuned pipe head flange to the exhaust manifold (three bolts one nut). When I took off the boot this morning I could see a loose chunk of gasket where the missing bolt was and some water stains. So I fogged the engine well. I followed all instructions as far as torque and loc-tite goes. But I read in one of the threads about using a copper exhaust gasket spray product. I used permatex ultra copper high temp. silicone gasket maker #101BR during reassembly. Also, is it practicle to take the pipe out with the carbs on?

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      • #4
        Re: 951 exhaust bolts loose

        First, if you used Loctite on the threads, you probably just did not get full torque on the bolts & nut. How did you tighten the nut?

        Second, the RTV you used is not the correct product, and will leak. The specified copper gasket treatment is a thin spray on product, not a silicone. Silicone should not be used anywhere on an engine.

        You need a new gasket set, and I highly suggest using the correct treatment, and making sure you properly torque all the fastners: http://www.sbtontheweb.com/Merchant2...gory_Code=51-1
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        • #5
          Re: 951 exhaust bolts loose

          I got the exhaust boot kit when I reassembled. I thought I got new bolts with loctite and fairly confident I had the torque right. I tighten the nut with the special wrench I also bought.
          Could it have been caused if something else was bad, engine mount etc.?
          Big mistake on the silicone, maybe that caused it. So at this point, is it just a reassembly and everything should be fine or could I have done some damage here?

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          • #6
            Re: 951 exhaust bolts loose

            Do a compression test. If you see a significant drop on one or both cylinders, you may need repairs/new engine. If that looks good, your running problems may have just been the exhaust leak.

            Did you use a torque wrench? I don't understand what you mean by 'fairly sure'. Even torque is critical on joints like this. If you did them all by hand, it's almost certain that they are either not to correct torque, or uneven, which will cause them to back out.
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            • #7
              Re: 951 exhaust bolts loose

              Yes I used a torque wrench. But "fairly confident" means I think I did it right, but somethings wrong so maybe I didn't! lol

              Anyway, on the compression test, can I do it on a cold engine? In other words, before I start to work on it?

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              • #8
                Re: 951 exhaust bolts loose

                Yes, you can do a compression test at any time - cold or hot only makes a psi or two difference.
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                • #9
                  Re: 951 exhaust bolts loose

                  Well, the compression test showed 130 psi mag and 120psi pto. So a couple of questions. If this is a fairly recent failure, I would think (hope) that the bottom end is "ok", and my fogging may have stopped the rust from setting in. If so, what needs to be done to the top end? In your experience what usually happens in these cases? I know I can't know for sure until I rip it apart, but I would appreciate an educated guess.

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                  • #10
                    Re: 951 exhaust bolts loose

                    Yes I would expect the bottom end to be ok, but you need to tear it down to make sure. You may be able to get away with a new top-end kit and hone the cylinders, but again, you'll need to tear it down first to know.
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                    • #11
                      Re: 951 exhaust bolts loose

                      I finally got back to this project. Pulled the head/cylinders off. I will need a new top end kit. Scoring on pistons and cylinders etc. From what I can see in the crankcase, I see no rust. The bearings on the connecting rod are all shiny. Now the question is do I need to split the crankcase to investigate further? Assuming I stop disassembly here, looks like I need the top end kit and the installation gasket kit. Anything else? The piston has a "1.00" stamped on the top, so I assume I will need the 1.5mm kit. Thanks again for your help.

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                      • #12
                        Re: 951 exhaust bolts loose

                        Yes you need to tear it dfon completely and hold the crank for inspection. If you need to bore further and want to do it yourself, yes you would need 1.5mm. We also offer a complete bolt-on top-end cylinder exchange kit too.
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                        We try to answer each question quickly and accurately.
                        Please do not use Private Messaging for Tech Support, use the forums.

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                        • #13
                          Re: 951 exhaust bolts loose

                          The only thing with the crank is the last 2 bearings on the pto end. They have the slightest of imperfection when spinning. All my gearhead buddies say all say it's fine and to reassemble. This goes against my gut, as 2 times taking this engine out is enough. So the determining factor is, how easy is it to replace just the last two bearings? I don't see them offered in your e-store, but I assume you sell them. How much? Also, as far as reassembly of the crankcase, what sealant do you recommend and how do I get the old gasket sealant off the plastic parts that are on the crank? I hope to order all parts today and get together next weekend, just in time for Labor Day, so I can then put away for the winter!

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                          • #14
                            Re: 951 exhaust bolts loose

                            Use parts cleaner and a gasket scraper to clean off the sealer. Use THreebond 1211 to reseal.

                            No we do not sell bearings - it takes a crank rebuilder to assemble crank parts - we only sell them complete. I do not advise using a crank with questionable condition bearings.
                            SBT Tech Support is here to help with your problems.
                            We try to answer each question quickly and accurately.
                            Please do not use Private Messaging for Tech Support, use the forums.

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                            • #15
                              Re: 951 exhaust bolts loose

                              I noticed during assembly that there is a discrepancy in your instructions. On the full "Engine Removal/Installation" instruction document it states in step 3.5 to torque the Allen Bolts to 18 ft. lbs and the Nut to 13ft lbs when attaching the Exhaust pipe. But on your instruction sheet that comes with your 951 gasket kit with pick-up envelope, it states to torque bolts to 35 ft. lbs and nut to 27lbs. Big difference.

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