I need some help, please. I'm changing the timing belt on my 91 NSX and made an incredibly stupid mistake. Don't know whether it's the 100 degree heat or just being very tired. Got all the alignment correct, put white marks on the old belt and each cam pulley and crank pulley, transfer white marks to new belt, got the old belt off and new belt on, take out the slack with slight counter clockwise motion on each cam pulley after staking the crank puley, roll tension clockwise per the manual. Now the disaster begins. For some unknown reason I rolled the front intake cam counterclockwise while holding the front exhaust cam and I'm nearly positive the intake cam jumped a tooth. I put a binder clip on each cam pulley and the crank puley to hold their position while I loosen the tensioner. Tensioner bolt is removed and I lift belt up and rotate intake cam clockwise one tooth. When I attempt to install the tensioner bolt, the whole tension pops off and the rear cams roll clockwise about 15 degrees. The binder clip for the rear intake is still in place wedged against the head but rear exhaust popped off. Long story short I have no confidence of proper alignment between the cam and crank. Can the motor be rolled over safely if I slacken all of the valve adjustment screws all the way out. All suggestions are welcome.
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timing belt disaster
- Thread starter SonnerBob
- Start date
Are you not using the punches/pins to keep the cams from moving? I think they are 5mm punches if I recall correctly.
There are holes that the punches go in. Are you using the factory manual or any type of guide that shows how to replace the belt step by step?
There are holes that the punches go in. Are you using the factory manual or any type of guide that shows how to replace the belt step by step?
I think you can do this without slackening the valve adjusters (I did it to mine). I found a spot while turning the crank where there was no tension. I then moved the cam gears by hand until the cams were aligned with their alignment holes. I then moved the crank to the TDC position and reinstalled the belt. I did this because on my first attempt I misaligned the rearmost cam by 2 teeth (a common occurance for first timers).
You must be VERY careful when doing this. The valves on this engine bend easily, so if you feel any resistance (I hope you took out the spark plugs) while turning the crank - STOP and feel which cam is binding, remove the punch/drill bit/nail that is holding the cam and release any tension before moving the crank again. I did this all by feel to make sure no valves were touching piston heads. It was unnerving to me so I know how you feel right now. Take your time, pay attention and you can get through this.
I'm sure LarryB and others here have more experience than me because I've only done this operation once. I have replaced many timing belts on other cars and this one was the most difficult by far.
Good Luck and keep us posted.
You must be VERY careful when doing this. The valves on this engine bend easily, so if you feel any resistance (I hope you took out the spark plugs) while turning the crank - STOP and feel which cam is binding, remove the punch/drill bit/nail that is holding the cam and release any tension before moving the crank again. I did this all by feel to make sure no valves were touching piston heads. It was unnerving to me so I know how you feel right now. Take your time, pay attention and you can get through this.
I'm sure LarryB and others here have more experience than me because I've only done this operation once. I have replaced many timing belts on other cars and this one was the most difficult by far.
Good Luck and keep us posted.
Biggest problem you have is that you should have removed the old timing belt in the TDC position, that also prevents to have a tension on any of the cams that can make it jump/turn as soon as you remove the belt!
My first advice would be for you to stop immediately and take the car to a professional shop, in neutral position to avoid the engine from turning.
You may not have any disaster yet, so don´t push your luck!
But somehow, something tells me you won´t, so here is my solutions:
Safer way would be for you to remove the cams, adjust the TDC and fit them back in the correct position.
Removing the adjustment screws will give you a lot of work, you may end up loose one or fall into the engine block (there are 24, that is a lot)
Then you would have all the valve adjustments to start from zero. By removing the cams you will still need to readjust the valves, but at least the offset will be much less.
Depending on the crankshaft position, you may get lucky and could perhaps try to rotate it with the belt in place back to the TDC position, always without any spark plugs, WITH EXTREME CAUTION AND STOP AS SOON AS IT FEELS BLOCKED!
Then if you get there, forget about your white marks on the timing belt that is not a correct way to do it!
Read the manual and use the cam pulleyy and harmonic balancer marks to find the TDC and the second mark where to re-tight the tensioner!
Remember to always rotate the engine in the clockwise motion!
Good luck!
My first advice would be for you to stop immediately and take the car to a professional shop, in neutral position to avoid the engine from turning.
You may not have any disaster yet, so don´t push your luck!
But somehow, something tells me you won´t, so here is my solutions:
Safer way would be for you to remove the cams, adjust the TDC and fit them back in the correct position.
Removing the adjustment screws will give you a lot of work, you may end up loose one or fall into the engine block (there are 24, that is a lot)
Then you would have all the valve adjustments to start from zero. By removing the cams you will still need to readjust the valves, but at least the offset will be much less.
Depending on the crankshaft position, you may get lucky and could perhaps try to rotate it with the belt in place back to the TDC position, always without any spark plugs, WITH EXTREME CAUTION AND STOP AS SOON AS IT FEELS BLOCKED!
Then if you get there, forget about your white marks on the timing belt that is not a correct way to do it!
Read the manual and use the cam pulleyy and harmonic balancer marks to find the TDC and the second mark where to re-tight the tensioner!
Remember to always rotate the engine in the clockwise motion!
Good luck!
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Thanks for everyone's input. I wanted address each person who responded.
For reply #1 - The cams were not pinned but the crank pulley was staked so it could not roll backward. I am working from the factory manual and write-ups from this site. Thanks
For reply #2 - Since I am uncertain the exact amount rear cams rolled clockwise, I realy don't want to roll them any more. I may already have bent valves in the rear head. Thanks
For reply #3 - I'm sure you are right, it might be cheaper in the long run to trailer it to a local shop. I have been working on cars for nearly 35 years and never had to do this, but there is always a first. Before removing the old belt I used the factory alignment marks (white stripe on the crank pully, TDC marks on each cam pulley). The white markds I made on the belt on pulley were back-up references (an old trick taught to me in the early 1970's by a Ferrari mechanic)
I'm going to back off the valve clearance adjusters but not attempt to turn the camshafts. I'm going to remove the new belt, remove the camshafts, re-set the crank pulley to TDC 1, re-install the camshafts with the correct timing orientation per the marks on the pulleys, pin the cams and re-install the belt. When I get to final tensioning I will very, very slowly roll the crank clockwise checking for any interference. If everything is good, I will check compression as a final test for bent valves. If it fails, off come the cylinder heads making this one long expensive project. I have only had one failure like this on an old Lotus Esprit. Thanks.
For reply #1 - The cams were not pinned but the crank pulley was staked so it could not roll backward. I am working from the factory manual and write-ups from this site. Thanks
For reply #2 - Since I am uncertain the exact amount rear cams rolled clockwise, I realy don't want to roll them any more. I may already have bent valves in the rear head. Thanks
For reply #3 - I'm sure you are right, it might be cheaper in the long run to trailer it to a local shop. I have been working on cars for nearly 35 years and never had to do this, but there is always a first. Before removing the old belt I used the factory alignment marks (white stripe on the crank pully, TDC marks on each cam pulley). The white markds I made on the belt on pulley were back-up references (an old trick taught to me in the early 1970's by a Ferrari mechanic)
I'm going to back off the valve clearance adjusters but not attempt to turn the camshafts. I'm going to remove the new belt, remove the camshafts, re-set the crank pulley to TDC 1, re-install the camshafts with the correct timing orientation per the marks on the pulleys, pin the cams and re-install the belt. When I get to final tensioning I will very, very slowly roll the crank clockwise checking for any interference. If everything is good, I will check compression as a final test for bent valves. If it fails, off come the cylinder heads making this one long expensive project. I have only had one failure like this on an old Lotus Esprit. Thanks.
LOL Good luck man. For what it's worth, about 10 years ago I did the exact same thing on another car of mine, fairly high compression V8 with very stiff valve springs. Let the cams get away from me and they jumped. I happened to be enrolled in an auto tech class at the time, and I told my instructor what happened. He completely brushed it off, saying not to worry. Doubt he had ever worked on an NSX, but if he hadn't seen it in 30+ years as a tech, I figured I was pretty safe. No issues with compression after I got it back together.
Also you probably already know this, but if #1 is at TDC (compression), then #5 is also at TDC (exhaust). Those are the 2 I would be worried about. The others are all 120* off from them.
Also you probably already know this, but if #1 is at TDC (compression), then #5 is also at TDC (exhaust). Those are the 2 I would be worried about. The others are all 120* off from them.
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Hope this isn't taking it off topic but...
What sayeth the forum of turning 1/8" drill bits upside-down and using them in lieu of the punches? What's the downside of that? What do the punches give apart from a thicker handle and a block from dropping down?
I mean assuming they're long enough that you are sure they won't drop beyond your reach.
I'm missing the overarching reason for using the punches, if not for the whole dropping-in thing.
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I have used drill bits. 5mm is a bit bigger than 3/16; you may as well get as close as you can. Smaller means your cams won't be aligned as closely as they would be with 5mm punches, but it's workable. As always take care with the alignment of the belt.
Bob do one thing, call an expert larry b ,I think he's done like 140ish belts,(including mine).
He's a great guy,shoot him a message,infact ill give him a call for you
Gary
He's a great guy,shoot him a message,infact ill give him a call for you
Gary
Thanks for the continued replies. Took the cams out last weekend and ordered new cam seals and plugs since it's all apart. Been out of town on business until this afternoon. Hopefully will receive the parts tomorrow so I can start reassembly. Supposed to be another lovely 107 degree weekend in beautiful Central Oklahoma. Will re-align the cams correctly with the crank at TDC and take another shot at the belt. Hopefully I can keep my head out my sweaty you know what this time.
Check your PM
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Hey guys,
I'm actually facing the same issue right now. I skipped a tooth on the front bank accidentally when reinstalling. I backed out all the valves and reset the cams and pulley individually to the TDC, I verified using the markings on the belt that I transferred over to ensure proper alignment.
But I've buttoned everything backup and as I'm adjusting the valves, I noticed that the TDC alignment is off. When the crank pulley is at the factory white marking, my cam pulleys do not line up to the TDC....
Should I be looking forward to another tear down to re-align the belts and cam? did I miss a step from my description above that would have caused this?
I'm actually facing the same issue right now. I skipped a tooth on the front bank accidentally when reinstalling. I backed out all the valves and reset the cams and pulley individually to the TDC, I verified using the markings on the belt that I transferred over to ensure proper alignment.
But I've buttoned everything backup and as I'm adjusting the valves, I noticed that the TDC alignment is off. When the crank pulley is at the factory white marking, my cam pulleys do not line up to the TDC....
Should I be looking forward to another tear down to re-align the belts and cam? did I miss a step from my description above that would have caused this?
I know Larry B's response was "Check your PM" (I usually hate reading those).... BUT - if you don't mind for those of us that are following this and learning from it, can you please cut&paste your PM message to this guy and put it up here so we can get your feelings/prespective/solution to this disaster. Thank you!
I followed the Gary Kentosh procedure down to the last detail, especially marking the cams and old belt and transferring those marks to the new belt.
I used a combination of pin punches and drill bits to hol;d hte cams in place.
What I noticed was when I put the new belt on and pulled "as hard as I could", I was one tooth off getting it over the front exhaust cam. I nearly stood on top of the engine, gave one more big tug, and got the belt even tighter so it moved one more tooth. At that point the "Kentosh mark" lined up perfectly for that cam, and the marks were quite easy to line up for the other 3 cams after that. So, at least from my experience (and I 've only done 2 TBs to date). the challenge was getting the belt tight enough for the "Kentosh mark" to line up with the front exhaust cam. Mess that up, and the crank will not align properly when the cams are at their TDC marks.
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ftuhy,
Thanks for the help. But I think I have it resolved. Tensioned the belt per OEM service manual and was able to get TDC to line up.
I do have one major concern that bugs me. The crank to cam ratio is 2:1, as in 720 deg turn of the crank is a 360 deg turn on the cam. So to return everything to the TDC, you need to rotate the crank by 720 deg.
However, I skipped a tooth, backed out all the valves and then reset everything to the TDC [or what I think the crank is at TDC], then put the belt back on. How do I know if the crank is 360 deg off though? This bugs me as I've already adjusted all the valves to spec and am now bugged by the thought that my crank pulley COULD be 360 deg off. Is there a check I can perform to ensure this? #1 cylinder should be in full compression at TDC so if I take the spark plug out, I should see the piston at the top right?
Thanks for the help. But I think I have it resolved. Tensioned the belt per OEM service manual and was able to get TDC to line up.
I do have one major concern that bugs me. The crank to cam ratio is 2:1, as in 720 deg turn of the crank is a 360 deg turn on the cam. So to return everything to the TDC, you need to rotate the crank by 720 deg.
However, I skipped a tooth, backed out all the valves and then reset everything to the TDC [or what I think the crank is at TDC], then put the belt back on. How do I know if the crank is 360 deg off though? This bugs me as I've already adjusted all the valves to spec and am now bugged by the thought that my crank pulley COULD be 360 deg off. Is there a check I can perform to ensure this? #1 cylinder should be in full compression at TDC so if I take the spark plug out, I should see the piston at the top right?
PM= Private Message
BTW, I asked him to call me to discuss, which he did not.
There is no way I would type out everything I was thinking about at the time.
Come to NSXPO2012 and join the tech sessions
Regards,
LarryB
I have some thoughts on the effect of the crank being 360 degrees off, but have not had my NSX engine apart to that extent. So, I'll leave this to others who have done such work.
Take it to a Acura delaership immediately, or to one of the very reputable NSX tech vendors, like Larry, Driving Ambitio, Autowave or SOS (that I know of).
Ship it there and then take a drive back.
It's a $10,000+ engine, not a $300 rebuilt Civic engine.
Ship it there and then take a drive back.
It's a $10,000+ engine, not a $300 rebuilt Civic engine.
I understand the valves have been described as very delicate, but is it really true that they can be bent by rotating the crank by hand if the cams are aligned incorrectly? I can understand it if the engine is cranked with the starter, but it just sounds unlikely to me that one could bend the valves applying torque by hand.
Are the physics of the torque multiplication via the various pulleys, etc., be enough to damage the valves?
Not being contentious here, just trying to understand. Thanks.
Are the physics of the torque multiplication via the various pulleys, etc., be enough to damage the valves?
Not being contentious here, just trying to understand. Thanks.
You obviously have never had an NSX valve in your hand
. You can do damage with a wrench easily....Regards,
LarryB
- Joined
- 19 August 2008
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Thanks....I'll look into that option if I can't resolve this myself.
Larry,
Is there a leak down or pressure test that I can run without starting the car? I currently have the spark plugs out and the valve covers off. I checked the height of cylinder #1 when the crank pulley is at TDC and it was all the way up. IF the crank pulley was off by 360 deg, the #1 piston would be down.. at the end of the compression stroke correct?
I am baffled by this continual reference to the crank being "off" by 360 degrees. 360 and 0 are the exact same position for the crank/pistons. What differs is where the cams are relative to the crank. TDC can be either on the compression stroke or on the exhaust stroke. The crank and pistons don't know the difference, only the valvetrain makes the determination of which stroke the engine is on.
IAm glad you asked I ve been wondering the same thing since I started reading this thread,360 is 360,I felt he was confused on valve event.
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- Joined
- 19 August 2008
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The ratio of the crank to cam pulley is 2:1. So every 360 deg turn of a cam is 720 deg turn on the crank pulley. I didn't know if this made a difference in the position of the cylinders or not.
I thought you can hypothetically lineup your crank position 360 deg off of the cam pulley so when your cams are at TDC, your crank is infact not....not sure if this is the case. But I wanted to get clarification before putting everything back together.
