james h
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| posted on 20/10/17 at 06:10 PM |
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Turning an engine over by hand - how freely should it turn?
As above!
I've taken the heads off the V8 in my '98 LS400, to diagnose a knocking/tapping sound (suspected bent valve due to hydrolocking from a
heavily leaking injector).
Both heads are off - I'd have thought the crank would turn consistently and freely - but no!
As cylinders 1 & 6 reach TDC (at the same time), it becomes very stiff to turn over. Is this normal for a V8?
Cheers!
James
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gary gsx
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| posted on 20/10/17 at 07:24 PM |
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Seems weird to bend a valve in that way did it lock solid? May of bent a rod.
Gary
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daviep
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| posted on 20/10/17 at 07:30 PM |
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Not familiar with this particular engine, is there a balancer or anything else driven from the crank that might affect rotation?
On a side note never heard of a valve bending due to hydraulicing, far more likely to bend a rod, have you checked that all pistons are coming up to
the same height? also look for unusual marks on the bore.
Cheers
Davie
“A truly great library contains something in it to offend everyone.”
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james h
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| posted on 20/10/17 at 07:47 PM |
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Just the harmonic balancer on the front, the belt is off. It's an auto, something in the transmission maybe?
My first job tomorrow in daylight is to check properly the bores and piston heights - a quick inspection shows it to be ok.
I'm thinking valves because the compression is about half what it should be on the cylinder which had the leaky injector (the compression test
wasn't done by me mind). Surely a slightly bent rod wouldn't cause such a massive drop in compression? Though I'm willing to be
educated on this topic!
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theconrodkid
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| posted on 20/10/17 at 07:55 PM |
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could be a bent rod, see if there is any height difference when pistons are at tdc
who cares who wins
pass the pork pies
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froggy
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| posted on 20/10/17 at 10:35 PM |
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Rods bend on these post 94 engines , I’ve done one on my turbo 1uz bending it until the underside of the piston hit the crank web
[IMG]http://i144.photobucket.com/albums/r187/froggy_0[IMG]
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rusty nuts
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| posted on 21/10/17 at 06:51 AM |
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If the injector was leaking to the point the cylinder suffered from a hydraulic lock it will more likely to have suffered bore wash than bend a valve.
Bore wash will cause wear to Pistons, rings and bore causing lost compression .Quick test for bent valve is to lay the head flat with both suspect
valves closed and fill the chamber with liquid( degreaser, petrol etc) then check the ports for signs of leakage.
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froggy
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| posted on 21/10/17 at 07:33 AM |
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I bent the rod until the piston hit the crank and it was only a couple of mm down in the bore at tdc
[IMG]http://i144.photobucket.com/albums/r187/froggy_0[IMG]
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perksy
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| posted on 21/10/17 at 11:46 AM |
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As above, Bent Rod ?
Saw this on a Subaru Imprezza once
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Sam_68
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| posted on 21/10/17 at 11:54 AM |
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quote:
Originally posted by james h
Both heads are off...
quote:
Originally posted by james h
I'm thinking valves ...
I'm confused... 
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ian locostzx9rc2
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| posted on 21/10/17 at 12:00 PM |
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It still could be something to do with the transmission?
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james h
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| posted on 21/10/17 at 12:52 PM |
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quote:
Originally posted by rusty nuts
If the injector was leaking to the point the cylinder suffered from a hydraulic lock it will more likely to have suffered bore wash than bend a valve.
Bore wash will cause wear to Pistons, rings and bore causing lost compression .Quick test for bent valve is to lay the head flat with both suspect
valves closed and fill the chamber with liquid( degreaser, petrol etc) then check the ports for signs of leakage.
I'll give this a go, thanks
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james h
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| posted on 21/10/17 at 12:55 PM |
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quote:
Originally posted by Sam_68
quote:
Originally posted by james h
Both heads are off...
quote:
Originally posted by james h
I'm thinking valves ...
I'm confused...
I took the heads off to send to a local engine specialist, (not sent just yet) to check over. I am not too confident on being able to spot a slightly
unseated valve. Although the technique mentioned before sounds useful.
My thinking being, if it's a damaged valve the heads will have to come off anyway, and if the rod is bent, the engine is buggered anyway.
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james h
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| posted on 21/10/17 at 04:08 PM |
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And the winner is.... Froggy!
Cylinder 8, TDC:
 
Cyl 8 TDC
Cylinder 7 (the one with the leaky injector), TDC:
 
Cyl 7 TDC
Time for a nice V8 coffee table.
The resistance turning the engine over was at Bdc for cyl 7. Clearly exactly the same happened to my engine, as it did to Froggy's. Bummer.
[Edited on 21/10/17 by james h]
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froggy
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| posted on 21/10/17 at 05:02 PM |
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I’ve got plenty of spare rods if you want one . It won’t have done any damage . I slapped a rod in mine and it’s fine and mines turboed
[IMG]http://i144.photobucket.com/albums/r187/froggy_0[IMG]
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mackei23b
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| posted on 21/10/17 at 05:48 PM |
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A big end bearing can give the same effect.
To check the big end when you rotate the crank and the piston stops moving for a period (almost like a flat spot) at the top this would indicate a big
end. Just to rule that one out....you did mention some knocking....
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froggy
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| posted on 21/10/17 at 05:59 PM |
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Knocking will be the underside of the piston scuffing the crank web .
In n/a form it’s pretty tough to damage a 1uz unless it’s got no oil in
[IMG]http://i144.photobucket.com/albums/r187/froggy_0[IMG]
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mackei23b
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| posted on 21/10/17 at 06:56 PM |
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Thanks, that would certainly explain the tight spot as well....
quote:
Originally posted by froggy
Knocking will be the underside of the piston scuffing the crank web .
In n/a form it’s pretty tough to damage a 1uz unless it’s got no oil in
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james h
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| posted on 22/10/17 at 02:10 PM |
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quote:
Originally posted by froggy
I’ve got plenty of spare rods if you want one . It won’t have done any damage . I slapped a rod in mine and it’s fine and mines turboed
I may very well be sending you a u2u soon! Thanks, that would be brilliant.
I have a limited mount of time I can put in to change the rods myself, but it might not take too long to get the engine out the car as it is now.
Whether or not I'm brave enough to attempt the whole job myself, I'll have to see!
Cheers
James
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froggy
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| posted on 22/10/17 at 02:32 PM |
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Pretty straight forward job . Just need to check the old head bolts for any aluminium from the block threads and clean them with a tap and airline
before building . Gasket sets and bolts are cheaper to have shipped from America than here as they’re hard to find anything non genuine
[IMG]http://i144.photobucket.com/albums/r187/froggy_0[IMG]
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coyoteboy
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| posted on 22/10/17 at 06:54 PM |
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Going back to the original question - I can't turn my V8 over by hand, even with the plugs out I need a wrench and a good 20lbft. My 3SGTE turns
over a bit easier, but that's not surprising as it has 4 fewer cyls with 1/2 the ring friction.
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daviep
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| posted on 22/10/17 at 07:53 PM |
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quote:
Originally posted by coyoteboy
Going back to the original question - I can't turn my V8 over by hand, even with the plugs out I need a wrench and a good 20lbft. My 3SGTE turns
over a bit easier, but that's not surprising as it has 4 fewer cyls with 1/2 the ring friction.
The cam(s) will make it lumpy even with plugs out, OP has the heads off so no cam effect so should be reasonably smooth.
“A truly great library contains something in it to offend everyone.”
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