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Old 03-22-2011, 02:41 PM
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454 rebuild, showing no compression

ok, looks like ther stuff hit the fan. I did a short rebuild on bbc, honed, new pistons, rings, cam, lifters, tchain, seals, gaskets and comes time to do first run in and its showing no compression (bouncing from 0 to about 40, but not holding). I didn't trust my old compression guage so i tried my older one, then bought a new one, all with same results. checked ring end gap, ok. checked valve adjustment, ok.

the rings are cast iron, cam is a mild rv cam (think its under 480 lift) hydrolic, springs are stock, rockers are stock, valves were within spec for play at the guides. The engine is a 1978 peanut port.

I backed off the rockers so there was plenty of play but still opened the valve, but still no compression.

any suggestions would be great.

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Old 03-22-2011, 04:25 PM
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Timing chain could be off. You need correct valve timing to make compression. Bring the piston up to tdc and watch the valve movement as you rotate the engine from there.

1 Intake should open as the piston starts down and should close when it is at the bottom

2 both valves should remain closed for compression stroke and power stroke

3 exhaust should open at the bottom and stay open as the piston rises. If one of the valves is opening on compression stroke it could cause what you are experiencing.
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Old 03-22-2011, 05:49 PM
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checked this two times and the valve timing is on. I'm gonna check it again tomorrow but if timing is on and rings are right what else could be causing?
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Old 03-22-2011, 06:05 PM
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This is really wild . The only two places that I know of where compression can leak off is pistons and valves . I assume that you staggered the ring end gaps .
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Old 03-22-2011, 07:09 PM
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second guessing Rat that dont Run

Got me puzzled, Had one once with very slow spinning starter that wound up showing low psi, but that was solved after correct ground was fixed, here come the tuff questions, Is it Std bore?? I know one fellow who swore his engine was and wound up with .020 pistons in the bores....with an .030 overbore,
Okay second scenario, lets play Columbo... at least us old timers... What caused the early demise of this Rat originally? Overheated, etc...
My suggestion shoot some 40w oil into each cylinder you can get to, hopefully hit them all, then get a compression reading or even better see if it starts...
Last one I can recall we were working in the really hot miami sun and wound up getting pushrods mixed help from too many helpers, but thats an really ugly story.... please keep us posted
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Old 03-22-2011, 07:12 PM
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But wait theres more....

Quote:
Originally Posted by Invstr396
Got me puzzled, Had one once with very slow spinning starter that wound up showing low psi, but that was solved after correct ground was fixed, here come the tuff questions, Is it Std bore?? I know one fellow who swore his engine was and wound up with .020 pistons in the bores....with an .030 overbore,
Okay second scenario, lets play Columbo... at least us old timers... What caused the early demise of this Rat originally? Overheated, etc...
My suggestion shoot some 40w oil into each cylinder you can get to, hopefully hit them all, then get a compression reading or even better see if it starts...
Last one I can recall we were working in the really hot miami sun and wound up getting pushrods mixed help from too many helpers, but thats an really ugly story.... please keep us posted
Sleeve
IS this guy spinning over with no spitting and backfiring? My guess is timing is way out and compression is there just going up the valve, check harmonic balancer did not slip on the outer ring and give you a false TDC... yeah that one bit me too!
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Old 03-22-2011, 09:33 PM
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Quote:
Originally Posted by theccrider
...its showing no compression (bouncing from 0 to about 40, but not holding).
Real good chance the timing set is incorrectly installed or you got a very badly ground camshaft. If the timing set has multiple keyways, be sure the marks are properly lined up. This is assuming the valve adjustment is positively not too tight, and the pistons and rings fit the cylinders as they should.

Ignition timing will not affect the compression gauge reading- the distributor can be laying on the bench and the compression readings would be the same as if the distributor were installed.
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Old 03-23-2011, 02:25 AM
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ring gaps are spaced correctly, ordered the pistons after pulling the old, they were standard. did the dry and wet test with no change on two cylinders. I got the engine about 18 yrs ago (I think Columbo was still on) and never fired it. don't know why I got it so cheap, but when I pulled it apart it had one bad (cracked) piston on the ring lands at the wrist pin. the timing chain is a comp unit dr lined up dot to dot, and the cam is from comp.

I'm gunna see if the cam timing is off today.
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Old 03-23-2011, 02:45 AM
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Are the heads torqued down? Are you sure the valves aren't rusty/stuck in their guides?
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Old 03-23-2011, 02:55 AM
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Quote:
Originally Posted by theccrider
the timing chain is a comp unit dr lined up dot to dot, and the cam is from comp.
Dot to dot? as in cam gear dot at 6 o'clock and cranck gear dot at 12 o'clock?
Tell me you didn't do that and drop the dist. in thinking it was at TDC.

On second thought, that would only matter if you tried to fire it up. sorry.
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Old 03-23-2011, 03:27 AM
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heads are torqued and heads were gone through. valves were free and clear with minmal play at guides. gaskets are fel pro and three stepped the torque sequence.
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Old 03-23-2011, 05:27 AM
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lost compression

i would start with a leak down test first before tearing that thing apart.check one cyl. at a time,make shure valves are closed and conect air pressure into spark plug hole and see if you can hear for air leak at exhaust or intake and crankcase this will rule out valve and ring leaks.
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Old 03-23-2011, 05:53 AM
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- 180* off on "timing" the chain (crank turns 2x for ever 1x of camshaft)
or
- valves not seating - adjustment, camshaft, lifters, pushrods
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Old 03-23-2011, 08:02 AM
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X2

Quote:
Originally Posted by Irelands child
- 180* off on "timing" the chain (crank turns 2x for ever 1x of camshaft)
or
- valves not seating - adjustment, camshaft, lifters, pushrods
X2 I second the motion, Try to get the damper at TDC and then check rockers on cylinder #1 to see relationship between #1 intake and #1 exhaust, my guess is you are 180 out at the cam/crank gear
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Old 03-23-2011, 09:06 AM
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Quote:
Originally Posted by theccrider
ok, looks like ther stuff hit the fan. I did a short rebuild on bbc, honed, new pistons, rings, cam, lifters, tchain, seals, gaskets and comes time to do first run in and its showing no compression (bouncing from 0 to about 40, but not holding). I didn't trust my old compression guage so i tried my older one, then bought a new one, all with same results. checked ring end gap, ok. checked valve adjustment, ok.

the rings are cast iron, cam is a mild rv cam (think its under 480 lift) hydrolic, springs are stock, rockers are stock, valves were within spec for play at the guides. The engine is a 1978 peanut port.

I backed off the rockers so there was plenty of play but still opened the valve, but still no compression.

any suggestions would be great.
Assuming all is good with the rebuild, are you doing a compression test because it wouldn't start? Somethings I would have to consider is, did you do a pre oiling of the engine? Did you use hydraulic lifters that haven't been totally filled with oil yet? and, are you doing the compression test properly as in removing all plugs, blocking the carb WO, and using a good battery for optimum cranking speed? Someone on this thread I believe has hit it on the head and we need to figure out exactly what it is as all suggestions have been pretty well valid on what can be wrong. You need to go back to square one and figure out whats going on after you clear your head and get over the frustration. I can only compare it to drawing a bead on a trophy buck with a muzzle loader only to hear a click when you pull the trigger. Don't blame the gun, right?
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