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Lost comp. on cyl. #4

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  • #31
    valve burning as pictured is most commonly caused by it not turning in the guide. The valve retention system, springs, collet, keeper and spring seat are designed to give a slight turn to the valve so that it comes down in a different spot on the seat. Looks like yours quit turning. Might also be, as Ken suggested, be very thin from being turned down too many times, but wonder with only 70K miles why that would have been done.
    :whistle:

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    • #32
      WOW, look how the burned valve is not centered over the seat. It's right on the edge where it burned through. I would suspect the valve guide is very worn and the valve is wobbling around, not closing true to the center of the seat, or the valve is slightly bent.




      EDIT: The entire exhaust valve head looks too small or the seat is too large. Compare this one from my friend's 73 after the stock valves were re-ground.









      Greg

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      • #33
        The carbon on #5 is very thick and centered under the valves (which are off center slightly toward the plug side of the cylinder). The other pistons have a light, even carbon cover. This tells me #5 has excessive oil leaking past one or more of the valve guides.

        My .02













        Greg

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        • #34
          I compared the head to others and it looks like it has the hardened exhaust seat on the bad valve. That's why it looks big. Still, doesn't that valve head look a smaller diameter than it should?

          Greg

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          • #35
            I see the difference Greg! And yes, the seats were exchanged for hardened ones back in 2009.

            The head was dropped-off at the shop this morning. Told the machinist to take everything off and check everything and anything he suggests should be done to it. He'll clean it and take it apart and call me on Monday with the results. I'll keep everyone posted.

            Also, I have decided to put the head on once it's finished. I still have until mid May of driving season left! :woohoo:

            Thanks again for everyone's responses,
            Robert
            3rd owner 1969 White/Blk TR6 Project Car with factory wire wheels and O/D. Owned since 2018

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            • #36
              Just chiming in but I agree with Greg about the oil seepage through the valves. I understand what your mechanic was talking about but the compression test result of 120 psi across this cylinder and the others would indicate that engine wear is normal and not excessive at this time. If rings and honing were needed wouldn't the compression test show lower pressures?
              1976 TR6 originally white now Porsche Voodoo Blue
              Frame off resto started May 2015
              Tshirts and TA boxes replaced
              Diff braced and reinforced
              Engine and head rebuilt
              Header and Intake ported
              SS exhaust
              Floors repaired, new metal at rear bumper mounting points
              New Rockers
              AAW wiring - GM alternator
              Complete suspension and brake rebuild, poly bushings

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              • #37
                Head came back from the shop and it looks much better now. :lol:



                I'll be assembling everything back today. Hoping it will be ready for Saturday's show !
                3rd owner 1969 White/Blk TR6 Project Car with factory wire wheels and O/D. Owned since 2018

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                • #38
                  I also inspected the tappets. This engine has received what I consider to be great maintenance. It's 73K miles now and Ialways used the ZDDP additive from the Roadster Factory in every oil change. I used Castrol GTX 20/50 with NAPA's Gold oil filter and changed it at the beginning of the driving season and at the end before summer storage. Averaging a total of 2,500 mile per year, I consider this good maintenance. I swiched to Valvoline VR1 20/50 about 3 years ago.
                  Unless the original owner,who drove the car for only 47K miles in 32 years didn't know about the ZDDP issue, I would like to know what else can be attributed to the awful condition of the tappets.



                  I checked the lobes and only one had a small amount of pitting from what I could see from above.
                  I guess that at 73K it is tired enough to give it a nice overhaul before the TRials...
                  Cheers,
                  Robert
                  3rd owner 1969 White/Blk TR6 Project Car with factory wire wheels and O/D. Owned since 2018

                  Comment


                  • #39
                    I see you have the car called 'original survivor'...but you also have quite a few modifications which kind of contradicts that classification.
                    With that in mind, has the cam, the tappets, the rocker arm ratio or the valve springs been changed from the original components ?
                    I ask because given reasonable care since new and based on what I've seen in high mileage engines, I don't believe original tappets would have looked like that.
                    Driving a 1973 TR6
                    Doing ZS carb repairs
                    email kencorsaw"at"aol.com

                    Comment


                    • #40
                      It makes you wonder what kind of process is going on to take random chunks like that out a lifter. When you visualize a flat part running against a spinning part, a bench grinder comes to mind and we all know what that wear looks like. On some lifters the wear patten looks relatively smooth without the pitting, more closely consistent with the bench grinding analogy.

                      Anyone know why some lifers pit and some wear evenly in the same engine?

                      Greg

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                      • #41
                        Spalling, typically happens to the softer of the two faces that interface, and greatly accelerates once the surface hardening that is (or should be) applied during manufacture wears through. Also, tappets are free to rotate in their bores, some more so than others, hence why the effect can appear across the face.

                        One of the best articles I read on the subject was written by Barney Gaylord, aka The MGA Guru. He visited our car-club a couple of years back, as he and his son were driving their MGA around the country.

                        MGA Guru - Spalling Article

                        Be sure to click the green "Forward" arrow at the bottom of the article - it goes on for several pages
                        Keith, Huntsville AL, 1971 CC66559U
                        10.0:1 CR gasflowed head | Weber DCOEs | CP "150hp" Cam | Good Parts Ram-Air induction | Distibutor by Advanced | Lightened flywheel | Phoenix SS Exhaust System | HVDA 5-Speed | Good Parts R200B Diff and CV axles | Good Parts suspension and anti-roll bars | Willwood Calipers and Vented Rotors | Good Parts Dual Brake Master Cylinder | Konig Rewinds | Boyd 15 gal tank | Miata Seats and Mr Mikes covers | Carl Visser dash | Mohair hood | Gas-strut bonnet and boot lift kits

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                        • #42


                          Head had the exhaust valves replaced along with the guides. Everything else was fine, including the seats. Also a new set of tappets.
                          No definite explanation as to why the valve burnt in the first place. Many variables to determine the one specific.
                          Car is running fine. Two more fuel tanks before re-torquing and adjusting valve clearance from suggested 0.012" to the 0.01".

                          Thanks for all the input!
                          Robert
                          3rd owner 1969 White/Blk TR6 Project Car with factory wire wheels and O/D. Owned since 2018

                          Comment


                          • #43
                            I see you have the car called 'original survivor'...but you also have quite a few modifications which kind of contradicts that classification.
                            With that in mind, has the cam, the tappets, the rocker arm ratio or the valve springs been changed from the original components ?
                            I ask because given reasonable care since new and based on what I've seen in high mileage engines, I don't believe original tappets would have looked like that.
                            PB,
                            The engine is stock. Modifications are centered in the suspension, brakes, and diff. only. Albeit, I modified my 6-Pack signature... B)
                            Robert
                            3rd owner 1969 White/Blk TR6 Project Car with factory wire wheels and O/D. Owned since 2018

                            Comment


                            • #44
                              Robert
                              break those new lifters in,run your motor at 2500 rpms, for 20 minutes and varie the rpm as well in the 20 minutes

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                              • #45
                                Hmm, thanks for the tip Phil, but too late for that. I've already driven the car 200 miles. I did put a big gunk of Moly assembly lube between lobes and bottom lifter, between inside of lifter and push rod, and between push rod and rocker. Plus I haven't revved it past 3,500. :blink:
                                Thanks!
                                Robert
                                3rd owner 1969 White/Blk TR6 Project Car with factory wire wheels and O/D. Owned since 2018

                                Comment

                                Lost comp. on cyl. #4

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