5.3l 1985 is on the bench .
I have cleaned and sealed it. Rotated it by crank nut, worked smoothly. To accurately find #1TDC I used the rod down the spark plug hole method. I may have sinned here : I rotated backwards and forwards. Later ,getting ready to install torque convertor I saw that it would not rotate past 40 BTDC CW and 18btdc CCW. So a dead zone of roughly 22* .
Pulling the 6 manifolds I could see all intake valve bottoms and fell all exhaust bottoms with a curved copper wire ( thinking a valve had fallen in ).
Pulled the dizzy, maybe it was stuck…all good.
I’m thinking if the chain tensioner was damaged it would jam the crank at intermittent degrees when I rotate crank, but it stops at the same places consistently.
I resealed the pan and sandwich platebut went no further into the lower section.
I replaced the front seal .
It feels like something is in the combustion chamber or maybe a crank lobe is hitting something.
Any ideas?? I am not really wanting to pull the pans again…they are sealed with Permatex right stuff!
Glen,
Give u history of the engine, was it sleeping in the yard for decade or coming from working car? Is it stripped or with ancillaries?
Have you tried to inspect cams under the rocker covers?
When you installed the torque converter did you make sure the bolts weren’t intruding on the back of the block?
I believe the problem is because of the counter rotation you performed. Somebody more experienced will be able to confirm/deny this.
thanks for the replies
engine was working fine before removal.
torque con not installed yet
I 'd like more opinions on what damage counter rotation might cause
On some engines the spring tension auto cam chain tensioners will allow enough slack in the cam chains that when the engine is rotated backwards the cam chains can climb over the cam chain sprockets teeth. This results in the camshaft repositioning itself and being out of proper timing that can allow the valves to contact the pistons among other things.
You can remove the valve covers and look at the cam tensioner. However I believe that you will have to remove the timing cover to properly check the tensioner and timing chain. A full retiming on the engine would be your starting point.
There should be timing chain plug somewhere - remove it and look inside, these tensioners are crap (you could snap it/released tension).
Can the engine be affected by reverse rotation - yes, especially when made by mazda. You have piece of tractor, not twin-cam construction, hence chances that chain jumper are residual, more possible it kinked (with tensioner on its last legs) - but this would resolve itself with the engine being moved again. Another option - broken/released tensioner, but i do believe that even with released tensioner the engine would work - giving massive rattle - without jump (take the plug out and pick tensioner with screwdriver to inspect obvious loose). Sapped tensioner can obviously cause block.
Three things:
- I understand engine still moves both ways with specific point of jam? Or… you’ve panicked and trying correct rotation only? (If so - reverse again)
- Front seal replaced is another suspect - is it possible you’ve pressed it too far? If so - cam chain can hook against secondary oil pump chain (at specific point due to no gap left).
- Have you installed all the pan bolts exactly as they were?
Also - how hard/how many degrees you’ve moved the engine for the first time?
I assuem you were turning it with ratchet / with spark plugs removed? How the jam feels? It it hard knock/instant or simply brakes and you cannot move it any further? You do realise it’s v12 with double-load on the cams, this will require bigger force to spin…
I rotated engine several times back & forward to find TDC…it was free then
Front seal is flush to cover.
All sparks are out ,it is a hard stop and very repeatable.
Bought an endoscope and tried looking in spark holes to see if a valve was hitting the piston but the focus was poor so I could not see well enough.
Cam covers off…tensioner is curved, chain is tight all the way around, I do not see any broken bits.
At #1 TDC B bank cam lines up well with the cam timing tool. A bank is almost 3 degrees ATDC when lined up. So not perfect but I calculate each cam tooth is 4.6* at the crank ( 360/42 then divide by 2). Hard to believe that small movement would cause my 22* lockup.
As far as pan bolts go…sandwich bolts are around the perimeter, only 4?? bolts in the middle of the pan are longer ( if I remember) but if I mixed up a short for long the problem would seem to be around the perimeter and not near any rotating parts. Please correct me if there is some way that the bolts could stop rotation.
On a different note. In pulling the plugs which I changed out 500 miles ago, there sure is a lot of crap that down inside the recess. Anyone find a cover of some sort to keep that clean ?? Any reliable way to clean hard crap off the tapered seats ?
The bottom view shows no potential interference in the mid section:
I suggest taking the front and rear pan bolts off and re-checking (leave the middle ones to hold assembly in place). With timing chain unaffected - this must be something easy to fix. With valve covers off - check all valves by depressing these slightly.
What if feels like? Hard lock, braking at specific moment?
The safest way forwsard would be to reverse everything being done. Apart from something colliding with crankshaft - you have only oil pump and aux shaft left, but you have already removed distributor…
Here is a photo of a tensioner. It is a broken one given to me just to try in an HE engine I was rebuilding many years ago. The break is at the lower pin bore, which is a weak point.
Usually that break is caused by the ROM technique for relieving the tension in the tensioner, which is to hook onto the top of the tensioner and haul it up. That puts enormous force on the lower pin bore which easily fractures.
Even so, it is not that likely the tensioner will fail if you simply reverse the engine rotation by hand.
I would use a borescope to look down the gap at the front of the heads and see if anything looks unusual.
I am guessing:
- You removed the heads, sandwhich plate and pan from the engine. You did not remove the timing cover. Is that correct ?
- You could then rotate the crank easily before fitting the heads and/or cams.
- Once the heads and cams were fitted and after timing 1A for TDC, that is when you discovered only 22deg of rotation possible.
Do not want to insult, but did you tighten the caps on the camshaft in the heads ( with heads fitted to block ) before making sure the camshafts were lined up correctly and 1A was at TDC ? Just a thought.
I once made the mistake many years ago of forgetting that important point when refitting the head on an old XJ6. That bent a valve which stayed down when it should be up, and prevented 360deg engine rotation. A tough engine, bought a new valve and all went well.
Something stuck on top of a piston would prevent rotation over maybe 60deg, but you would have 300deg of rotation. Same goes for one bent valve.
You would need at least 2 bent valves, and probably more depending on location, to restrict rotation to only 22deg. You can check the bent valve theory looking for clearance between cam lobes and tappets.
Offhand I cannot remember if it is possible that a 5.3L HE valve at max opening will hit a piston. The exhaust valve is recessed so much less likely to hit.
I understand he removed covers only for inspection purposes. The cams were intact.
You only really have three possibilities:-
1/ a valve or valves stay low (either relative to crank position or just generally). Since you have the cam covers off, disconnect the camshafts and loosen the cam caps and try to rotate by hand. If it rotates, then it was a valve versus piston height problem because all of the valves should be high now. If it is still going to lock, then…
2/ you have something fallen into the chain via the timing cover and you cannot turn the crank OR
3/ you have a tight engine because the webs on the crank are fouling the conrods. This’d happen if the thrust washer allows the crank to move forwards excessively and the conrods are now not moving vertically up and down - they are at enough of a skew angle to the vertical that they rub or bind.
Essentially if you pass 1/ then you have a bottom end problem.
Turning the engine backwards is not necessarily a problem, so long as the tensioner is fully tensioned. During normal operation, the chain is accelerating and tensioning the chain fully, but it is also going to decelerate rapidly when revs drop and when this happens, the tensioner is the only thing keeping your timing in one piece. Relatively speaking, it is trying to go backwards fast.
There are some pictures in my old photo albums about where a good versus bad tensioner sit relative to the centreline of the engine and that should give you a steer as to how worn your chain may be.
You might not notice if the revs are constant or increasing, but the classic symptom is that a running engine dropping from high to low revs rattles like hell as the chain makes metal to metal contact.
kind regards
Marek
Glen, have you been moving the engine on the bench vertically at some point / at angle?
Heads were not touched.
As I rotate the crank I check all valve shims . They are free so no stuck valves.
I think the next thing is to pull the timing cover ,remove the chain and see if crank still locks up. So I will be looking to replace the chain & tensioner while I’m there.
May sound dumb…could something besides a stuck valve have gotten into the spark plug hole and is blocking the piston
Removed timing cover…yes I broke the tensioner ( old & very brittle) but that was not the problem. Removed lower pans and shield…nothing blocking rotation there. Removed timing chain , loosened cams . Put cams and chain back on it rotated properly. After many inspections of the combustion chamber through plug hole and finding nothing , I rotated 20 times and no problems now.
Not sure what the original blockage was but I’m satisfied now.
New chain & tensioner on order!!
In many many ways, better this happened now than later on the highway.
With a broken tensioner, you probably pulled the Bbank out of sync a little bit every time when rotating backwards to find tdc and perhaps the chain could have skipped a tooth at the jackshaft sprocket.
Very lucky to find it now, not later. Imagine how much extra work it’d have been if the engine were in the car.
kind regards
Marek