Compression & Ignition Question

Discussion in 'Street/strip 400/430/455' started by Johny Bee O, Jan 29, 2011.

  1. Robs455

    Robs455 Well-Known Member

    Yes there are with the black coating.
    The machineguy bore and honed the cylinders. He used his special machine. Cylinder 3 is scratched with verticals strips, the same are one the piston. This scratched area is widen by 0.4mm 0.015" and is in under/middle of the cylinder. Now i need to know whats the correct cylinder diameter, i guess it has to less space..

    Thanks

    Robert
     
  2. RG67BEAST

    RG67BEAST Platinum Level Contributor

    Looks like too tight piston to wall clearance to me. Spec is .0025" but .003" will do. With those pistons each should be measured .500" from the bottom of the skirt. Not perpendicular to the pin like cast pistons as the skirts on these l2353's are wider at the bottom.
    I don't know why you would have a crooked valve. Is the valve head bent and not seating? If so you likely had a mechanical mishap.
    The correct cylinder diam is 4.342" for a .030" over 455. The clearance is built into the piston. The machinist should have already known this and measured the pistons ahead of time.
    Ray
     
    Last edited: Dec 1, 2011
  3. Gary Bohannon

    Gary Bohannon Well-Known Member

    DETONATION is a possibility.

    Fel Pro gaskets are good safety devices. They will blow before the engine blows.
    So, a blown Fel Pro and piston wall scratches could indicate too much pressure and heat.
    1. Make sure you're not leaning out and never go full power at more than 180 degrees eng temp.
    2. Make sure your cranking compression is below 200 psi or that your dynamic compression is 8.0 or less

    Do this before you spend more $$$.
    Get an air/fuel meter and also check fuel flow/pressure and maximum mechanical timming.
     
  4. DaWildcat

    DaWildcat Platinum Level Contributor

    My thoughts as well. Could explain both the gasket issues (both banks!) and excessive side loading/rocking of the piston skirts. If so, I'd be concerned about the health of the main and rod bearings too.

    Devon
     
  5. Robs455

    Robs455 Well-Known Member

    Should i hear a detonation? water was 185F @ dynorun. Detonation can be a cause. The waterpasses on the gasket are small. But there are many reason for these blown gasket. I mean the area from the 3(4) Cylinder is very small to the middle of the engine...
    First i would to try is verifying the correct piston to wall clearance. Ray thanks for your advice, can you tell me how i messure the true piston to wall clearance? Im a little confused, its hear me like the piston have not overall the same diameter? So i should measure it 0.05" from ground of the skirt? :Do No:
     
  6. 71stagegs

    71stagegs bpg member #1417

  7. DaWildcat

    DaWildcat Platinum Level Contributor


    Piston skirt diameter is measured at 90 to the pin in this location:

    [​IMG]

    And no, you won't always hear detonation. We're not suggesting it is the only root cause of your problem, only that it should be considered.

    Devon
     
  8. 462 Chevelle

    462 Chevelle 462 chevelle

    like devon said. a good inspection of the rod bearings may or may not confirm detonation if it is only on the messed up cylinders. was it ever running lean?
     
  9. pmuller9

    pmuller9 Well-Known Member

    Robert initially measured the intake valve to piston clearance as .078"
    which is under the recommended .100" clearance.

    This led us to beleive the cam was possibly advanced too far.

    Robert, I would still like to see the 1.27mm lobe lift timing numbers for intake and exhaust opening and closing before you take the cam out.

    Robert reported a cranking compression of 12 to 13 BAR which puts it under 200 psi which made us figure the cam position was OK.
    I believe these readings were taken after the first dyno pull so they could be low.
    However if the cam is advanced alot that can also contribute to detonation.

    The initial dyno pull was done with a total advance of 35 degrees and backed down to 30 on the next pull.

    There where problems with the first carburator, it was running rich with a Lambda reading of 0.7 or 10.3 a/f ratio
    It was only a 750 cfm so it was decided to change to an 870
    but you could here the compression leaking past the head gaskets at an idle at that point which would indicate the damage had already been done.
    The new carb ran better with a Lambda reading of .85 or 12.5 a/f ratio

    Robert, you mentioned problems with the valves. Is it the intake or exhaust valves that look bent?

    Paul
     
    Last edited: Dec 3, 2011
  10. RG67BEAST

    RG67BEAST Platinum Level Contributor

    Rob I only read your rant on post 159. I was in a hurry and did't eneven notice the head gasket blow out. Upon reading other posts and looking at the pictures I agree with others you had a severe detonation problem.

    The first order of business is tear the engine down and wash it out even the crank passages. Like you are doing brain surgery. Clean Clean Clean.
    Keep the lifters in proper order of their lifter bores. For the center pistons look for any abnormal wear. If the rings on the center bores are glazed and excessively sharp on the bottom compared to the others new rings are required. Look at all the rod bearings. For sure you will have to redegree the cam for all it's opening and closing points. There was a pressure issue happening. First disassemble and we can go step by step from there. Don't get discouraged.
    Ray
     
  11. Robs455

    Robs455 Well-Known Member

    Paul the .078" was with a wrong degreed cam. I degreed the cam intake @ 114 and exhaust 122. It is an intake valve. The engine is complete disassembled, i will make pictures from the bearings.

    After 3 Pulls and no changing in AFR with the 750 i tried it with the orginal 850cfm. But hes condition was worst not seal...
    The engine was running 10 Seconds with a very lean 1.3 Lambda (2000rpm 50lb/ft). After that we use the 870.
    The engine made pull after pull more pressure in the crankkase till the last pull 3800 RPM wheres the headgasket complete was gone and a big steam like a steam locomotive. After that we shout down the engine and my heart was broken! Since this day i dont like dynos!

    Robert
     
  12. pmuller9

    pmuller9 Well-Known Member

    Robert

    How thick does the head gasket measure?

    Paul
     
    Last edited: Dec 1, 2011
  13. Robs455

    Robs455 Well-Known Member

    Its a standart Felpro 0.40 and on the TA Page is the max CR 10.5:1 . Could they blow off from my CR? and after that the pistons gets slapped to the wall, because the leak in the head?
     
  14. RG67BEAST

    RG67BEAST Platinum Level Contributor

  15. Robs455

    Robs455 Well-Known Member

    Here is a Link with pictures from the engine and rodbearings. Thanks for your advice:idea2:
     
  16. pmuller9

    pmuller9 Well-Known Member

    Robert

    Do all the rod bearings look like picture #2
    Does the rod cap half of the bearing also look like picture #2

    Are any of the piston rings broken?
    Are any of the top piston rings pinched in the groove?

    You can see in pictures 10 and 11 where the intake valve hit the piston edge
    You may need to notch the pistons to give more clearance

    The chipped piston edge in pictures 12, 13 and 14 may have happened if there was detonation going on.

    Cam lobes look good

    Have you had the chance to check piston to cylinder wall clearances?

    Paul
     
  17. Robs455

    Robs455 Well-Known Member

    Update:

    The rod caps bearings annd other bearings looks like them from picture 2. Why?

    No Ring is broken or pinched in his groove. But there should be a problem, watch on the picture.

    The worst cylinder has a diameter difference from .0015" . The machineguy is back from USA and recommend a rehoning only. Because this are big pistons and the not slap so fast like smallers...

    Today i compared a scratched piston with one with less scratchers. The massiv scratched piston has a diameter from 110.19mm vs. 110.17mm, bore was or is 110.28mm - 110.30mm.
     

    Attached Files:

  18. pmuller9

    pmuller9 Well-Known Member

     
    Last edited: Dec 7, 2011
  19. pmuller9

    pmuller9 Well-Known Member

    The reason I asked for the 1.27mm (.050") and the 0.15mm (.006") lobe lift readings for both the intake and exhaust lobes on the cam
    was to determine the actual dynamic compression ratio and the valve overlap. It was not just for the cam position.

    That was back in post #74 and post #97

    I still would like those readings

    Paul
     
  20. Robs455

    Robs455 Well-Known Member

    Were the rods re sized after installing new rod bolts? U mean measure the roundness of rods-bearing and correct size?
    I push the rod-bolts with a hammer in and torque with the factory numbers.

    Paul, how torque your head-bolts right? with oil and 100lb/ft? i use arp bolts.
    And, what u would do in my situation? Now my engine make me sick... i would like throw it in to the trash..

    The machineshopman recommend me a rehoning only. Because these are big pistons and they not slap so fast like smallers. Only the area from the middle to the bottom is 0.0015" wider than the top. what u think about it?

    For me is the next step to pickup a large paper and measure all piston and cylinders down,middle,top. I hope these numbers bring me more light in the dark...


    Thanks for your adive :gp:
     

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