Why are the Tercel valves adjusted hot?

[Jooseppi Luna]

I was looking at the FSM and it puzzled me to see that the valves are adjusted while hot. My '84 Mercedes-Benz 300D Turbo Diesel is adjusted cold, which makes more sense to me (who wants to remove a hot valve cover?). Why are the Tercel valves adjusted hot?

[Petros]

the relationship between the steel valve train and the aluminum head changes as the engine heats up, you can adjust the cold, but you get noticeably more valve train noise. Aluminum gets larger than steel with the same increase in the temp. It will not harm anything to run with slightly large gaps, the adjustment will just be a bit too big, and noisy. when done with the engine warm you measure the actually running gap with all the parts warmed to the operating size.

[Jooseppi Luna]

the relationship between the steel valve train and the aluminum head changes as the engine heats up, you can adjust the cold, but you get noticeably more valve train noise. Aluminum gets larger than steel with the same increase in the temp. It will not harm anything to run with slightly large gaps, the adjustment will just be a bit too big, and noisy. when done with the engine warm you measure the actually running gap with all the parts warmed to the operating size.

Hmmm. So could you adjust them hot, and then measure the valve clearances when cold (say, the morning after the adjustment), and then adjust them cold with those clearances in the future?

[teranfirbt]

That's one way to do it.

[TURTCEL]

I would not recommend thinking that the clearence that you would measure when cold after a hot adjustment would be an accurate way to do it for future jobs. Over time engine parts wear and since it recommended that the valves be checked every 12k miles (who really does that) you can bet that the clearences may be slightly different the next time.

And really what would be the benefit of doing it cold since the odds are you will just have to redo it right after that after you warm it up. I have always liked using a pair of leather mechanics gloves for jobs like this. The engine needs to be up to operating temp to do the job correctly but if you let the car sit for a couple minutes after warming up so you can remove a not so hot valve cover it will not be long enough to cool the engine to where your clearences would not be accurate. Work smarter not harder.

I have found that the fast food drive thru window has caused this world to want everything to speed up so things can get done quicker. I find this is when mistakes and wasted time come in to play. Do it the right way first so you don't add unecessary stress to yourself. The guys on the website know what they are talking about so consider their advice...they have seen it all before and made the mistakes or avoided them so they can let others know their secrets.

Peace

[Jooseppi Luna]

I would not recommend thinking that the clearence that you would measure when cold after a hot adjustment would be an accurate way to do it for future jobs. Over time engine parts wear and since it recommended that the valves be checked every 12k miles (who really does that) you can bet that the clearences may be slightly different the next time.

And really what would be the benefit of doing it cold since the odds are you will just have to redo it right after that after you warm it up. I have always liked using a pair of leather mechanics gloves for jobs like this. The engine needs to be up to operating temp to do the job correctly but if you let the car sit for a couple minutes after warming up so you can remove a not so hot valve cover it will not be long enough to cool the engine to where your clearences would not be accurate. Work smarter not harder.

I have found that the fast food drive thru window has caused this world to want everything to speed up so things can get done quicker. I find this is when mistakes and wasted time come in to play. Do it the right way first so you don't add unecessary stress to yourself. The guys on the website know what they are talking about so consider their advice...they have seen it all before and made the mistakes or avoided them so they can let others know their secrets.

Peace

Oh, my concern is not with speed, but with not burning my hand. I've done that way too many times already! Sounds like it can be done relatively painlessly, so I'll stop whining

[TURTCEL]

Hey man I didn't take anything you said as whining. I hate burning my hands too. The thing that is nice is that the aluminum valve cover cools pretty quickly in relation to the head. It is thinner and if you just wait about 3 mins after warm up the cover should be cool enough to handle.

A tip on the valve cover replacement. If the gasket is not new you need to replace it when you do the valve adjustment. These gaskets get hard and brittle over time from heat and can crack or just not seal anymore. Make sure to replace the rubber half moon seals at the front and back of the head too. You can buy a valve cover gasket kit with or without the half moons. Use a tiny amount of sealer (I like Hi-Tack) to hold the half moons in place while installing cover. Also a little bit of silicone between the the valve cover seal and the half moons has always helped keep a good seal on my Toyotas.

These covers only have 3 nuts holding them down and from the factory they are assembled using a three socket machine that tightens and torques the cover down all at the same time. Since you can't do this tighten the cover nuts down evenly and slowly to the proper torque spec. These cover are a notrious problem child for leaking. Improper torque on anyone of the three nuts can cause a leak that is a pain to stop sometimes. You can also have a friend help and one of you can tighten two nuts and the other can tighten one all at the same time so the evenness of tightening can be as close as possible. Just dont overtighten...some think that when it is so tight it won't tighten anymore that it is good, this is usually when a problem starts. Seals can get pinched, pushed out, or cut from overtightening.

Good luck on the project...it ia basic one but the other tips are nice to know too. I suggest adjusting the valves and then rechecking them a day later to see if there is any clatter that may still need to be adjusted out. A little noise is common on these cars but too much means the clearances are too far off and the car might not be running to its fullest potential.

Peace

[Jooseppi Luna]

Hey man I didn't take anything you said as whining. I hate burning my hands too. The thing that is nice is that the aluminum valve cover cools pretty quickly in relation to the head. It is thinner and if you just wait about 3 mins after warm up the cover should be cool enough to handle.

A tip on the valve cover replacement. If the gasket is not new you need to replace it when you do the valve adjustment. These gaskets get hard and brittle over time from heat and can crack or just not seal anymore. Make sure to replace the rubber half moon seals at the front and back of the head too. You can buy a valve cover gasket kit with or without the half moons. Use a tiny amount of sealer (I like Hi-Tack) to hold the half moons in place while installing cover. Also a little bit of silicone between the the valve cover seal and the half moons has always helped keep a good seal on my Toyotas.

These covers only have 3 nuts holding them down and from the factory they are assembled using a three socket machine that tightens and torques the cover down all at the same time. Since you can't do this tighten the cover nuts down evenly and slowly to the proper torque spec. These cover are a notrious problem child for leaking. Improper torque on anyone of the three nuts can cause a leak that is a pain to stop sometimes. You can also have a friend help and one of you can tighten two nuts and the other can tighten one all at the same time so the evenness of tightening can be as close as possible. Just dont overtighten...some think that when it is so tight it won't tighten anymore that it is good, this is usually when a problem starts. Seals can get pinched, pushed out, or cut from overtightening.

Good luck on the project...it ia basic one but the other tips are nice to know too. I suggest adjusting the valves and then rechecking them a day later to see if there is any clatter that may still need to be adjusted out. A little noise is common on these cars but too much means the clearances are too far off and the car might not be running to its fullest potential.

Peace

Don't worry, I construed myself as "whining" without any help from you! I actually don't own (or maintain) one of these cars, because there were none around when I was trying to buy a car (I went with the aforementioned '84 300D instead). I was just reading through the FSM for fun and wondered why the valves are adjusted hot, since in my (100% cast iron block) Mercedes the valves are adjusted cold.

[ARCHINSTL]

Mercedes diesels have valves?
Tom M.

[Petros]

I just wait until the valves are annoyingly noisy to adjust them, that is about 30k miles, so it does not have to be done often. I have done it cold, but always find it makes too much ticking noise. Do it with a warm engine, it will be tight and quite for a long time.

Also, install the valve cover carefully, you could warp it or even crack it if over tightens, or if not tightened evenly. New gasket or used, I always put a lot of sealant on the valve cover gasket (I hate leaks), this way I do not have to over tighten the valve cover to prevent leaks. I have seen over tightened valve covers, the will tighten and than go "pop" and a crack forms suddenly (I have never done it, but I have seen others over-muscle engine parts to do such damage). you have to throw it away if that happens.

[Jooseppi Luna]

Mercedes diesels have valves?
Tom M.

Yes. Why wouldn't they? They don't have spark plugs or throttle valves, but they sure have intake/exhaust valves (10 of them in the Inline-5)!

http://dieselgiant.com/valveadjustment.htm

[ARCHINSTL]

Mercedes diesels have valves?
Tom M.

Yes. Why wouldn't they? They don't have spark plugs or throttle valves, but they sure have intake/exhaust valves (10 of them in the Inline-5)!http://dieselgiant.com/valveadjustment.htm

OK - excuse my ignorance; I thought all diesels, from their beginning, had direct injection of some type, obviating the need for conventional valves. I bow.
Tom M.

[teranfirbt]

I would not recommend thinking that the clearence that you would measure when cold after a hot adjustment would be an accurate way to do it for future jobs. Over time engine parts wear and since it recommended that the valves be checked every 12k miles (who really does that) you can bet that the clearences may be slightly different the next time.

If the valves are measured directly after a hot adjustment then wear doesn't matter... Metal expands and contracts based on the laws of physics, not wear rates. As long as the cold clearances are set the same each time, then the hot clearance will be the same.
My method usually involves not burning myself and just setting them a thou on the tight side cold, has yet to fail me.

[Jooseppi Luna]

OK - excuse my ignorance; I thought all diesels, from their beginning, had direct injection of some type, obviating the need for conventional valves. I bow.
Tom M.

I'm sorry, I didn't mean to come across as arrogant -- most (if not all) new diesels utilize direct injection, but my car is 28 years old, and the engine family in it dates back to the early 70's, so I have indirect injection.

EDIT - from ARCHINSTL: I did not take your response as arrogant. I tend to write in a now-archaic style (perhaps because I am antediluvian?).

[TURTCEL]

To teranfirbt
"If the valves are measured directly after a hot adjustment then wear doesn't matter... Metal expands and contracts based on the laws of physics, not wear rates. As long as the cold clearances are set the same each time, then the hot clearance will be the same.
My method usually involves not burning myself and just setting them a thou on the tight side cold, has yet to fail me.[/quote]

I agree that the clearences "should not" be different but Toyotas have been known to have some issues with the hardened tip on the rocker arm that contacts the valve stem. The hardened tip can come off of the rocker arm and you can ajust the clearence out but it will soon start to clatter and readjustment will only fix the prob for a short time.

The rocker arm would need to be replaced if this is the case. Over time parts will wear especially if the parts are worn and are continued to be run that way. Also, valve springs loose tension overtime and a weak spring can cause adjustment issues.

Do what you want but why keep running the possibility of redoing the job over right after you did it? Check your valvetrain everytime you do a valve adjustment to assure that all parts are in good condition. I have done warm and cold valve adjustments on my Yotas before only to find that a hot adjustment is the way to go. To each their own and how they do things, many ways will work and we we all have different results with different methods.

This website is open to having many opinions on how to do things from member posts and that is why it rocks. Use the tips that work best for you.

Peace














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