So to start off, I own a 95 UCF20 with the interference engine. I started to put on my new timing belt yesterday, its not my first timing belt change but never on a 8 cylinder engine, as usual i put the engine on tdc, of course with the cam gears on the right position, the marks on that engine are pretty obvious. Then I put the belt on, again with those marks on the right spots, really nice that those toyota timing belts have that specific marks on them. After that i released the tensioner and double checked all the marks again, until this point everything went perfect as it should. Then off course I wanted to do the 2 full revolutions by hand to be sure, so i removed the spark plugs and started to turn clockwise, I did one revolution with no problems but then after another 1/4 there was a strong resistance, I wasnt able to move it further and of course I didnt apply any strong force. I was really surprised, that never happened to me before, especially because i knew for 100% that the marks were corrent. I turned it again counterclockwise to recheck the marks, but now comes the really strange thing, after 1/2 turn backwards i had the same strong resistance even though i already made over 1 revolution, so of course i wasnt able to get to my starting point, tdc. But i was able to set the crankshaft to tdc, but the wrong one, due to that 1 rotation I already made, as a result the camshafts were offseted by 180 degrees. At that point i couldnt move any further without removing the belt again. I moved the crank around 1/8 turn, so that there is no piston at tdc, this made me able to rotate the camshafts freely. I put them back a the right spot, as well as the crankshaft, refitted the timing belt, double double check all marks and then tried it again clockwise. But no luck I got stuck at exactly the some position as before, counterclockwise the same. The max. rotation that Im able to do is not a full 1/2 turn more like 170 degree, so 85 degrees clockwise/counterclockwise from tdc. At this point i really didnt know what just happend, the only thing that came in mind for me was that I was maybe hitting valves, but that made no real sense because the marks were correct all the time. But still I wanted to confirm that, so i removed both valvecovers, to see what the valves are doing. Every 1/4 rotation 2 cylinders reach tdc, at engine tdc we have cylinder 1 and 6, 1/4 turn clockwise cylinder 8 and 5, 1/4 turn counterclockwise cylinder 2 and 3, of course i wasnt able to check the tdc of cylinder 3 and 7 because due to that issue Im not able to turn the crank far enough. In that test i could confirm that the timing of all camshafts matches with the piston positions, so when a piston gets to tdc all valves were shut, on all the previously mentiond cylinders, i also check the cylinders with open valves when the crank gets stuck, but they were, as they should, far away from tdc. I check the position of the pistons trough the spark plug holes. I also thought about bent valves, even though i didnt apply any force, but all valves returned to the fully closed position when i rotated the camshafts. But im pretty sure when there would have been bent valves i would be able to spin the engine. I should also mention that point were the crankshaft gets stuck never changes even slightly, I even tried to rotate the camshafts separately (of course without any force) form the crankshafts to move valves, that i could possibly hit, out of the way, or maybe move the problem to a different position. But this didnt made any difference. At that point I was sure that Im not hitting any valves or that I have any timing issues, I thought what could else block the crankshaft? There isnt that much attached to the crankshaft. The first thing that came in mind was the starter, maybe it did not return fully and the flywheel gets caught up there. It was already pretty late in the evening and i thought it would be a good idea to spin the starter for a short pulse to maybe solve that unlikely starter issue, i know not the best idea but i knew the timing was right so i shouldnt been able to bent any valves. I did that, the engine made about 1 full turn, I had put the engine right at that resistive point clockwise, so that the starter wasnt able to hammer through that stuck point, honestly even with that, the starter was able to make that turn easyly. I had another person watch the movement, otherwise I wouldnt have know how many revs it made. So again 1 revolution, again 180 degree off tdc, but this time i was able to turn it again 1 revolution to get to the right tdc, i was really happy. Check again the marks, all fitted well, then the next try to make the 2 revolutions by hand .... but no again stuck after 85 degree, same as before. I checked the valves and camshafts again as before, still all as it should be. I currently out of ideas and I really never saw or heard of anything like that and I really need the car at the moment. Maybe one of you guys have some more ideas or had something like that before. The only thing i could still think of is that the oil pump randomly got stuck? I applied a lot of heat at the crank pulley to get it loose. hmmm ... Thank You

 

Because there's no obvious visual reason for the engine to be locking up as you describe, I think you're going to have to have to go through a process of elimination diagnosis. Even though it appears unlikely, you first need to eliminate any doubt that there's no valve/piston interference occurring.

You can try to measure valve clearances; it doesn't matter what the clearance is, just that there IS clearance. If you can't measure clearance while the valve is on the camshaft base circle, it's not too much work to remove the camshafts and measure the valve spring heights. Hopefully, with the camshafts removed the valves should all be on their seats and you'll be able to rotate the crankshaft to see if the lockup still occurs.

If you have the camshafts out, you can use something similar to this - check Amazon: (https://www.lislecorp.com/specialty-...e/valve-holder). Apply a little air pressure into each combustion chamber and listen for leakage.

 

Just last night I had a similar issue. I bought a 99 that was run with no bolts in the cam gear (eventually worked loose and tore things up). I pulled the cam and put it back together and have the same mysterious resistance about the same place you describe.

My thoughts on next steps:
turn the crankshaft over with no cam belt and the cams all at the +50 degree location.
turn the cams on each bank with no cam belt and the crank at the +50 degree location.

I'm in the midst of removing all the accessories and such off the front of the motor. I'll let everyone know what I find.


Rich

 

I know I've read about this same symptom a few times here over the years but I don't remember any cause. Ya might be able to find something about it if ya search other subjects that connect with the T-belt, cams, or crank.
Just a suggestion, not one of those "search" posts.

 

I found one of the posts you referred to deanshark. One of the timing belt idler pulleys was seized and prevented the engine from turning.

Still searching for others.


Rich

 

FWIW, after installing the belt and tensioner, my '98 FSM reads:

18. CHECK VALVE TIMING

(a) Temporarily install the crankshaft pulley bolt.
(b) Slowly turn the crankshaft pulley 2 revolutions from TDC to TDC.

NOTICE: Always turn the crankshaft pulley clockwise.

Doesn't explain why your engine hit a hard stop while turning it CW. I think rotating the engine CCW refers to engines that have the VVT-i system.

 

BNastee did the engine run without the bolt in the camgear? The gear did not get loose? .. I figured out my problem - really stupid one - as I said before my timing was correct at all times .. as paulo said I did check the camshafts and I could definitely rule out any stuck valves, all returned as they should. At the same time I found a thread in a german forum that had the exact same problem on his MX5 NA (non interference engine) - he disassembled his engine to figure it out - he drove only short distances for years with that car of course the engine ended up with a lot of carbon build up - he guessed when he used the impact gun and hammer to break the crank pulley loose some of that carbon got loose and blocked cylinders. As you might gues my engine also has a **** ton of carbon build up (next problem I have to figure out) and needed almost half an hour with an impact gun to break my pulley loose, so at lot of impulsive vibrations. After that the first time I tried to turn the engine over was with the new timing belt, when the issue came. Now in my case I poured some WD40 into the cylinders and then I used pressurized air to blow through the cylinders - and yes that freed everything up .. spinned freely after that. I put everything back together and tried starting it - fired right up and runs absolutely perfect

Maybe you got the same issue? Kinda funny that something that stupid can cause so much trouble. In sour case I would definitely check the valves if they return properly. Did you made any progress?

 

What are the odds of that happening? Kinda crazy but makes sense. I'm glad you got yours turning again.

 

Hey Ralph. It did NOT run. It would crank and occasionally fire. I remember hearing the sound-while-cranking change and I think that's when the cam gear came off the VVTi actuator.

I tore it down yesterday and found the problem. I wish it were just some loose carbon. Two of the valves are stuck down. Huge gap between the cup and the camshaft with the lobe on the base circle. Today I'll be yanking the cylinder head. I'm hoping for bent valves that can be swapped out. If the seats are ripped out it's an expensive job.


Rich