Help w/577 Carb Motor
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Ok here is the story: 577 motors with Big Brodie heads w/ 1050 carb Crane Hi-6m Box with MSD Dist. Crane Roller Cam#139661 with morel lifters. Timing set at 14 base and 34 total, all in at 3000rpm’s. Port motor runs strong with no problems what so ever turning a 28P B1 prop. Starboard motor ran great and the only problem was a crack around the head bolt boss close to cyl#6. Ran 15 hours this way… with the only problem was water leaking from the crack into bilge.
Removed head to have crack fixed and machine shop found 2 springs on #8 broken. Did valve job and replaced 2 broken springs. All other springs measured fine. Put head back on and new problem developed. Idles fine and runs good until put under load. At 3000 rpm’s backfire thru intake…OK I think valves too tight…readjust valves… gets worse when hot. Readjust again….same problem. Also motor will only make 4400-4500rpm WOT. Before both motors ran 5200RPM’s.
Ok here is what I have done: Switched Carbs, coil, Ing Box, Coil wire, and new Fuel Pumps. Fuel pressure is 9psi at idle and around 5psi WOT both motors. Oh I have adjusted the valves so many different ways I can do it in my sleep. Just did a compression test and all cyls are 170 to 175 on all cyls. On Port motor they are 175 to 185 Bought a leakdown tester and I don’t know if the readings are correct or not but it shows 30-35 % loss and all cyls on both motors, so I don’t think this is correct. I am going to try a different leak down tester.
So as you can see this all started when the 1 head was R&R. The Port motor still runs strong…Any help and advice..would be greatly apprenticed.
Removed head to have crack fixed and machine shop found 2 springs on #8 broken. Did valve job and replaced 2 broken springs. All other springs measured fine. Put head back on and new problem developed. Idles fine and runs good until put under load. At 3000 rpm’s backfire thru intake…OK I think valves too tight…readjust valves… gets worse when hot. Readjust again….same problem. Also motor will only make 4400-4500rpm WOT. Before both motors ran 5200RPM’s.
Ok here is what I have done: Switched Carbs, coil, Ing Box, Coil wire, and new Fuel Pumps. Fuel pressure is 9psi at idle and around 5psi WOT both motors. Oh I have adjusted the valves so many different ways I can do it in my sleep. Just did a compression test and all cyls are 170 to 175 on all cyls. On Port motor they are 175 to 185 Bought a leakdown tester and I don’t know if the readings are correct or not but it shows 30-35 % loss and all cyls on both motors, so I don’t think this is correct. I am going to try a different leak down tester.
So as you can see this all started when the 1 head was R&R. The Port motor still runs strong…Any help and advice..would be greatly apprenticed.
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I would spend an hour or so with a dial indicator and check your cam lobes if you had some broken springs a lifter may have been "floating" and the impact may have flattened a lobe just an idea............. (you should be able to do this w/out pulling the cam)
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Originally Posted by rumblfish1966
I would spend an hour or so with a dial indicator and check your cam lobes if you had some broken springs a lifter may have been "floating" and the impact may have flattened a lobe just an idea............. (you should be able to do this w/out pulling the cam)
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I think i found the problem....I went back to square 1 and started checking everything. I decided to start with the cylinder #8 that had the broken valve springs. I found the lifter on #8 Intake collapsed. When checking with a dial indicator it open fine but there is no movement or spring action from inside the lifter... I think I finally find the Gremlin.
Anyone have a pair of Morel lifters they want to part with.
Anyone have a pair of Morel lifters they want to part with.
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I had the same problem with the Comp Cam's top of the line hydraulic roller lifters....colapsed plunger/spring inside the lifter. I was fortunate enough that it didn't do any further damage to anything else in the engine. Replaced both engines with Morel lifters. A nice feature about the Morels is that they can be totally rebuilt for about $200.
What kind of valve springs are you using? Have you ever tried any of the Isky brand tool valve springs?
What kind of valve springs are you using? Have you ever tried any of the Isky brand tool valve springs?
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Well that did not fix my problem. Man I was so sure it would...next step... Would having the wrong seat pressure also cause b/f under load. I'm thinking the machine shop that repaired the head did not set the springs correctly.... am i off base...
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Maybe you have a slightly bent intake valve due to the prior weak springs. Popping out of the intake makes this a good guess. You should be able to remove the intake valve spring without removing the head. Do that and spin the valve checking for a tight spot.
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Bingo...took head off, took it to a head shop and intake valve was bent...If weather holds up this week I will test this weekend..thanks for all the info.
Hope this thread helps someone in the future...