Valve Timing Adjustment

[BackToTheBog]

Greetings, all.
During the spring I made a cross-country trip in my '98 Cruiser. The vehicle exceeded all my expectations and got me out of more than one jam on the muddy trails of North-Eastern Nevada. She took a beating for the whole two-month trip, but got me home and dry without any problems.
Recently, I've gone over the vehicle and changed out some seals (rear pinion and axle) and a front axle. I thought I was getting off lightly until she started idling rough and spat out the dreaded P0300 codes. It read P0300, P0302, P0304, P0306 and P0308. The entire passenger-side bank was misfiring. After a couple of minutes idling, I could see fuel dripping from the exhaust joint just after the muffler.
I suspected that the valve timing was off so I removed the left and right timing belt covers, set the crank shaft to "0" and noticed that the passenger-side cam gear was retarded by two teeth.
My question is, is it possible to advance the passenger-side cam gear two teeth by somehow relieving tension on the timing belt? I really don't want to remove all the components necessary to change the timing belt and was wondering if there are any short cuts or tricks to advancing the passenger-side cam gear to its proper position.
Thanks.

 

[2001LC]

Rare for belt to slip, in fact by the looks of yours (no teeth missing right?) it solid.

Last time I did my TB, before buttoning back up, I tried setting back too zero. What I found is I couldn’t get all three points (cams & crank) to lined up anymore with belt timing marks. If I keep turning crank it may have gotten back, but I realized it doesn't line up all three with belt each time crank turns back to zero, but it does line up with cam marks.

Your problem may be elsewhere.

 

[BackToTheBog]

Yes, the belt is solid and all teeth seem to be intact. I should have mentioned that I found some remains of a rodent (probably a mouse) under the driver-side TB cover. I'm not sure how it got in there, but it might have something to do with the slip.

 

[2001LC]

Doubtfully, it would just eat that mouse.

That said I went back and look at some notes and it was the timing marks on the belt I could not line up with cams.

The belt may have slipped, but if so you may have a problem with belt tensioner. How many miles on belt & water pump etc….

 

[2001LC]

Did you slowly turn crank pulley (with wrench) 2 revolultions clockwise from TDC to TDC?

 

[BackToTheBog]

Last TB change was at 126K (has 210K now), so 84K. WP is original.
Yes, i slowly turned the crank pulley around twice, but used a ratchet and socket instead of a wrench.
I'm getting o.k. fuel pressure on that bank, so I don't know what else it could be besides the valve timing.

 

[OregonLC]

Doubtfully, it would just eat that mouse.

Mouse-sized debris could definitely create havoc. Unless a cover was left off, I can't imagine how one would get in there... but it's completely plausible that if a mouse was between the belt and the gear the resulting 'hump' would cause the gear to move under the belt.

The two cam gears move at a 1:2 ratio to the crank, there is no delta between left and right. You may get 1/2 degree slop with stretch and flex but that's it.

I would definitely not drive it until the source of the problem was identified. And I'm sure you're aware, but the belt is getting other debris ('dirt') on it that will accelerate wear. The belt compartment isn't an operating room or anything, but it's designed to keep things reasonably clean. IIRC, there is a small cover plate that's easy to forget when you're putting it back together after replacing the t-belt. Is it possible that your shop left it out? Would explain both the dirt and the mouse.

 

[marshotel]

Did you check for spark on that cylinder bank?

I think all the ignition circuits (ignition coils) for each cylinder bank share a ground somewhere back towards the firewall.

Seems like if that ground came loose, then you might have ignition problems like you describe.

The other thing I would check is the exhaust for that cylinder bank: obstructed exhaust could cause misfiring for the entire bank.

I'd be surprised if it ran at all if the timing was off by two teeth.

Be careful with having lots of unburned fuel in your exhaust; if your catalytic converters start glowing red, then you are gonna have problems....

 

[BackToTheBog]

I'll lift it tomorrow and check for the cover plate. The previous owner (according to receipts) had the TB changed at the dealership about 10k before I bought it.

 

[Sandroad]

Taking a mouse for a ride around that pulley would make an awful mess. Is there any recent evidence of that? I can't see how the belt could slip cogs, even if a mouse was in there. If the tensioner is ok, it's just too tight on that pulley. Rodents can do lots of wiring damage, so you should check wiring going to the PS cylinders and the grounds if you've had mice in the engine.

 

[TXLX100]

For what it's worth, I've seen shredded drive belt debris get in the timing cover and cause the t-belt to jump. Also, I've seen a rodent get caught in the drive belt and cause it to fall off the pulleys. So it's entirely possible a rodent getting caught could cause the belt to slip a tooth.

 

[2001LC]

Greetings, all.
******. She took a beating for the whole two-month trip, ****** *******. The entire passenger-side bank was misfiring. After a couple of minutes idling, I could see fuel dripping from the exhaust joint just after the muffler.
*****My question is, is it possible to advance the passenger-side cam gear two teeth by somehow relieving tension on the timing belt? I really don't want to remove all the components necessary to change the timing belt and was wondering if there are any short cuts or tricks to advancing the passenger-side cam gear to its proper position.
Thanks.

Are you sure it was fuel, could it have been condensation?

If you removed sprocket and replaced back in at timing mark, you’d most like do a lot of damage, its and all or nothing deal.

******* IIRC, there is a small cover plate that's easy to forget when you're putting it back together after replacing the t-belt. Is it possible that your shop left it out? Would explain both the dirt and the mouse.

OregonLC, is this the cover: no. 2 which sit between DS & PS belt covers, its actually touching the PS belt cover and can be seen from top looking down, the one you suspect may be missing?

I'll lift it tomorrow and check for the cover plate. The previous owner (according to receipts) had the TB changed at the dealership about 10k before I bought it.

How about posting a picture of that same cam sprocket but looking down so we can see the #2 timing belt cover?

I'd, closely inspect every tooth of timing belt without twisting it, look for chunks missing, and check sides. Look for any damage, nicks or wear, cracks etc.. If damaged replace.

That said, the discoloration on the belt is presumable from whatever foreign object was in belt enclosure. This could lead to premature failure of belt and since your close now to the recommended mileage change, I'd been inclined to change belt and water pump and be prepare to RR idlers and tensioner.

But, I’m still skeptical the belt is your problem, but it possible I guess. TXLX100 said he's seen a mouse take off a drive belt. These timing belts are strong and tight provided tensioner is working properly. Risky but you could run engine while watching belt>>>>>>> hey you already had it running right.



Was your air filter, air box and air induction tubes to throttle body intact day and night, so nothing could crawl up and nest?

Cleaning your throttle body is always a good idea.

 

[2001LC]

******IIRC, there is a small cover plate that's easy to forget when you're putting it back together after replacing the t-belt. Is it possible that your shop left it out? Would explain both the dirt and the mouse.

This must be the small cover you're speaking of, nice deduction OregonLC (seen in post number 9 picture) a DUST SHIELD: https://forum.ih8mud.com/100-series-cruisers/148025-90k-starter-replacement-job.html

 

[OregonLC]

Very crude drawing of how Mickey (or other debris) could cause teeth to migrate. As the belt pulls away from the gear it would cause the teeth to engage earlier on the pulley and therefore retard the timing.

 

[Trunk Monkey]

I think you're vastly overestimating the strength of Mickey's skull and you'd still have plenty of teeth in contact.

 

[2001LC]

Plausible^^^^^^^^^^^, you’re making me a believer.

Do you think any damage was done when he ran it?

 

[OregonLC]

I think you're vastly overestimating the strength of Mickey's skull and you'd still have plenty of teeth in contact.

Maybe, maybe not. It's not about the strength, it's about the volume of incompressible mass. Anyone who has installed a belt knows you don't have to pull the belt away from the gear by more than about 1/4" to get it to roll over a tooth. And you're not getting the entire circumference to skip, you're just starting the rotation with one tooth off and then this 'error' rolls over the top.

 

[OregonLC]

Plausible^^^^^^^^^^^, you’re making me a believer.

Do you think any damage was done when he ran it?

You'd be hearing bad noises if any true damage was done. The only 'damage' right now is that your timing is off. If it were me, I'd start afresh with a new t-belt job, but then I have the tools and space and mine isn't a DD. I'd worry more about the longevity of the belt considering how dirty things look in there, although the 100s are known to operate well past their t-belt interval without fail.

 

[bamachem]

I think you're vastly overestimating the strength of Mickey's skull and you'd still have plenty of teeth in contact.

Not really.

The contact point would start at the pinch point where the belt would begin to roll over the pulley. Since there would be something between the belt and the pulley, the teeth couldn't make contact with each other. The result is that although the mouse is crushed between the pulley and the belt, there is still a mass there which has an effect to increase the effective diameter of the pulley as far as the belt is concerned. Therefore, with a single rotation of approximately 180-degrees of mating surface, an effective diameter change of just a few percent can be enough to change the belt-pulley relationship by a couple of teeth.

There are 48 teeth on a cam pulley. To jump 2 teeth in 180-degrees of rotation, you only need a deviation of approximately 8% in overall diameter.

------- Jumping 2 teeth in 180-degrees of rotoation means an effect of 4 teeth for the whole 360-degrees. 52/48 = 1.0833 or 8.33% increase

Assuming a 4" diameter cam pulley, a deflection of approximately .16" would be enough to create the 8% increase in diameter.

------- The diameter is 4" and we know it jumped 2 teeth in 180-degrees, requiring a 8% defelction for the effective radius. (4" / 2) = 2" radius. 2" X 1.0833 = 2.1667" is the effective diameter needed.

We are talking about a 3 sixteenths of an inch of deflection here! (3/16" = .1875"). So, if the mouse gets crushed to only 3/16" thick for the 180-degree rotation, then the belt can and will jump 2 teeth on it's relative timing with the crank pulley.

 

[2001LC]

The case for Mickey is growing stronger.

You could use the same mickey logic of raising the belt by inserting a hard wooden dowel while turning crank with socket and cam as needed, to get it aligned again. Then see if it will run normal again. But a TB job is still in order and the risk of damage to belt and values/pistons is high.

So to answer your question IMHO: NO short cuts or ticks, do the TB job and see..