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1G Very low compression - no start

Posted by 91tsiawdtalon4g63, Oct 11, 2018

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  1. 91tsiawdtalon4g63

    91tsiawdtalon4g63 Proven Member

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    1990 gsx, 0 mile only idle time 6 bolt block I bought from a reputable seller in the community. 6 bolt cylinder head, new topline lifters (bled before installed), kelford 272s, oem valves that were lapped in by myself and my friend. Brand new gsc beehive valve springs and retainers. Brand new 9627pt felpro head gasket with L19 studs torqued to 115ft/lbs, brand new timing belt pulleys tensioner etc.

    We fully assemble the entire build and drop it into the car. We gap brand new plugs and toss them in and hit the key. It cranks but doesn't fire up so we wait a little then it finally fires up for 5 seconds then dies out and won't even try to fire again. So we pull the head thinking bent valves but all the valves are 100% good, then we think maybe timing belt slipped but everything lines up and belt is 100% good. We run a compression test and get 40-75-40-100 (1-2-3-4). It's a fresh block so rings aren't seated yet but we have zero idea what is wrong that the car won't even attempt to fire. My friend and I have spent 2 straight weeks mulling and replacing parts that we would even suspect to be the issue yet absolutely nothing has changed anything.

    We did a poor man's leak down test and it is coming from the oil galleries in the head to indicate rings but they're not seated so I'd assume that they should leak right now. The pistons are wossner with eagle rods. Unknown on specs from the rings as it was built prior to me owing it. Cylinder walls look excellent.

    I asked the seller of the block his opinion on this and he says that it sounds like valvetrain. So before we swap all the goodies to a different head, Any input would be great to solve this huge PITA
     

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  2. motomattx

    motomattx Proven Member

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    Sounds like pinched rings or something of the like, even brand new engines should develop plenty of compression to start and run, it might be a LITTLE low, but nothing like that. Have you tried a different compression tester? how are you doing the test? wide open throttle and crank it until the needle quits moving is the proper way, also make sure the tester has a schrader valve installed in it or it wont read right.
     

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  3. 91tsiawdtalon4g63

    91tsiawdtalon4g63 Proven Member

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    Tried 2, an advance auto one and a harbor freight. Both read the same :/

    Yes wot crank til the needle stops and yes on the valve.

    Dropping a cap full of oil raised the compression but still wouldn't get it to fire.

    Is there any way to check for a pinched ring without a complete disassembly? Not really wanting to tear it back apart with a track rental coming up in about 16 days...
     

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  4. donniekak

    donniekak DSM Wiseman

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    I’d have the head checked. You should be able to hit 40psi without rings on the pistons.
     

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  5. 91tsiawdtalon4g63

    91tsiawdtalon4g63 Proven Member

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    My buddy and I lapped in the valves and used a straight edge to make sure it isn't completely mukked up. Could it be possible that a valve got bent but doesn't show any signs of it being bent?
     

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  6. arrowhead

    arrowhead Proven Member

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    Valves not valve.
    what were you trying to see with the straight edge?
     

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  7. 91tsiawdtalon4g63

    91tsiawdtalon4g63 Proven Member

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    Straight edge to see head straightness on the gasket side.
     

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  8. amsrn13

    amsrn13 Freelancer

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    Something is wrong with the shortblock. The fact that the rings arent “seated” is irrelevant, my new built engine made 150 on the dot on each cylinder with 0 run time. You probably should of pulled the pistons out to verify the piston to wall clearance and ring gaps. At the end of the day unless you see it with your own eyes .....its not guaranteed
     

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  9. donniekak

    donniekak DSM Wiseman

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    I’ve seen cylinders with melted pistons make 40psi. I’m not saying his shortblock is fine, but that for compression that low you have a valve or timing issue.


    It’s also very possible that the lifters are hanging valves open. I’ve seen people do that a lot installing lifters wrong.

    Before tearing anything apart a leakdown test should be done. That will tell you exactly what the issue is.
     

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  10. 91tsiawdtalon4g63

    91tsiawdtalon4g63 Proven Member

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    I blew 3 pistons apart and I drove the car almost 13 miles afterwards and the numbers were close to 40...

    Bled them til they were squishy, never soaked them in oil, took the toplines straight from the box and bled then installed them

    Neither of us have a true leak down tester but filling the cylinders with air from the compression tester setup, all the air is coming through the oil galleries with the valve cover off. We actuated each valve to see if they would maintain the same sounds or not and upon opening each valve the air changed pitch and the air went with the each valve we opened whether intake or exhaust.
     

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  11. 91tsiawdtalon4g63

    91tsiawdtalon4g63 Proven Member

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    I have talked with the seller of the block and he says that the block is healthy and brought a weird question into the equation. He says that he has seen kelford cams installed backwards (ie. Intake where exhaust should be and vice versa). This is the first kelfords i've ever had and I'm pretty sure that they install one way (cas on intake) but is their anyway to install the cams wrong?

    They were torqued in and in the proper way. I'm just baffled really.

    Not saying you aren't correct in the least. I'm just trying for it not to be the shortblock LOL I know whenever we added a cap of oil to each cylinder the compression rose but being dished pistons that would be obvious that the numbers would increase.
     
    Last edited by a moderator: Oct 24, 2018

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  12. amsrn13

    amsrn13 Freelancer

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    The only piece of the engine you are relatively certain about is the head. You had the head apart, lapped the valves and installed a new headgasket. That why im leaning towards a block issue. Those compression numbers are also very random. You could drop the pan and take a look at the rods, check for play?
     

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  13. pauleyman

    pauleyman DSM Wiseman

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    Valve train. Run a leakdown. All else fails pull the cams and do a leakdown. You will know for sure at that point. Yiu can build a leakdown tester if you don't have one.
     

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  14. Vegas smith

    Vegas smith Proven Member

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    It's 2018. Get on amazon and get a leakdown tester for $30 to your door tomorrow :)
     

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  15. donniekak

    donniekak DSM Wiseman

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    I have kelford 272’s in my car and had to open up the lsa about 10* to get over 15 in/hg at idle.

    I wouldn’t doubt if you had a combination of issues. Pull the rockers (or cams) and do a real leakdown. You’re going to have a good amount leak past the rings because they’re new, but I’d also pull the manifolds so you can check how much is getting past the valves.
     

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  16. 91tsiawdtalon4g63

    91tsiawdtalon4g63 Proven Member

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    My buddy and I are going to put another head on the car today to rule out anything resulting in head issues then I will respond back here. Thank you all very much for all the info given
     

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  17. 91tsiawdtalon4g63

    91tsiawdtalon4g63 Proven Member

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    Replaced the head completely with a great condition head and the compression actually became worse on all 4 cylinders. Zero bent valves, everything 100% so the short block is the issue.
     

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  18. motomattx

    motomattx Proven Member

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    Yup.
     

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  19. 91tsiawdtalon4g63

    91tsiawdtalon4g63 Proven Member

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    You were the first to call it. I just had some hopes that it wouldn't be :(
     

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  20. pauleyman

    pauleyman DSM Wiseman

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    I'm gonna go on a limb here....did you make sure the crank plate isnt on backwards? You eliminated the head/cams but to have such low compression just doesnt seem likely unless something isnt lined up.
     

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  21. tametalon92

    tametalon92 Supporting VIP

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    Sounds like bad head gasket surfaces or effed rings.
    I don't see why the compression test results would get worse (granted, don't know how much worse) from the head swap unless the gasket is leaking across cylinders or something got messed up on install.

    What was the block surface like, what gasket used, etc? Not saying the short block isn't the issue, but can't hurt to check the whole picture.
     

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  22. 10's or bust

    10's or bust Proven Member

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    Willing to bet you any amount of money that the ring gaps are out of spec and or the piston to cylinder walls clearances are not within spec.At this level of disassembly it doesn't take that much longer to inspect these clearances and this could be done with even with the block inside of car.
    8
     
  23. motomattx

    motomattx Proven Member

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    Someone could have installed standard rings or pistons on a bored block, who knows... Are you certain that the exhaust isnt plugged up in any way?
     

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  24. donniekak

    donniekak DSM Wiseman

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    ^^^^^^^^
     

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  25. motomattx

    motomattx Proven Member

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    Could be^^^ I would think there would be bent valves at some point though.
     

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