valve guide replacement
 

I was wondering what is involved in replacing the valve guides.

I am working on an engine, it's not a mercedes engine, but soon I will be doing the same on my mercedes engine, and was wondering how this process is carried out exactly.

This engine I have in pieces now is the Mitsubishi 3.0L V6 commonly found in many Chrysler cars.

I have both cylinder heads off, and it looks like some of the valve guides have "dropped", so I want to fix this up and put the car back together.

Assuming that the valves are still good, and will not be replaced, is it just taking the valve out with the assistance of a valve spring compressor, tossing out the old one and putting on a new vlave guide and seal and putting the valve back on?

Is griding necessary or anything else like that? I will be doing this for the first time, so any hints and tips will be greatly appreciated.

xp

VAvle guides are pressed in. Some have a shoulder, some have an E-washer or snap ring, and some have to be seated to correct depth with a guage. Some just get pushed in til they stop. Engine dependent, so you must check. You will need the press tool as well -- usually a pilot that fits through the guide.

The are removed with a tool by pushing them out from the bottom.

You will probably need to grind the seat to restore the sealing surface. May or may not have to ream the guide for correct size -- MB guides will be exact and won't require reaming, but other manufactures sometimes do. Seat conditioning must be done after the new guides are in place, as they are the reference for the seat (ie the valve must sit correctly to seal).

Lapping the valves in is also required to get a good initial seal.

I'd have a shop do all this. You can install the valves yourself, but have the machine work done, it requires far to many tools to do yourself.

Valves can be ground if not too badly worn, there is a spec for how thin the edge can be. The shop will tell you if you need new ones. Intakes usually can be reused (less wear), exhuasts usually must be replaced.

Peter

pricey
 

I took both the heads to a machine shop close by, after calling a few others. They told me they would do everything on them for $4500 each. This is a $500 car and no way can I spend, not that I even have this kind of money. Additionally, it's an extra car that I would love to get working right, but if I don't then it is no big loss, just a ton of spare parts for the one my dad drives, it's the same thing esentially.

This is why I'd like to do all this work on my own, I have time since I don't need the car, my dad has all sorts of measuring equipement since he works in a machine shop like that as well, just does not deal with cars. In other words tools and other devices I can get. So it would be a much better deal for me to just resurface the heads at a specialty shop and do the rest myself.

I'll be getting the heads back on Monday, the valve parts are not pricey at all, and if I can get this car working then kudos for me :)

Unfortunately, the Haynes manual for this car does not have a procedure for doing this which would be helpful, so I will be looking for some type of a guide to replacing valve guides :)

xp

Do you do your own brain surgery also. I've heard it is expensive too.

I have had a saying that has applied my whole life to almost every endeavor. "The best thing you can know about an operation is what you don't know". What you don't know, you can figure out. If you don't know that you don't know, you are screwed. It is part of life to figure this out. You have a lot to learn.

Machinist tools won't cut valves or seats. The common measuring tools might tell you if you needed to or not, if a knowledgeable machinist were making the adaptations. I doubt that a standard machine shop would have 9mm go-no-go gauges for measuring guide wear. You might possibly have a 9mm interference reamer.

By asking the question originally you point to your lack of knowledge. Continue finding what you don't know and you will be less confident and more sure.

BTW: $4500 to repair one head, what were they doing recreating it atom by vacuum deposited atom? I don't even think 928 S4 heads cost $4500 new.

Many of the heads used in modern 4 valve applications were never meant to be repaired after major failure. I know almost nothing about Mitsu heads except that they grenade when the belts break. Working on a MB head is infinitely more doable than a Mitsu head, part of the reason the car costs 3 times as much.

$4,500. each?????????????
You must have misunderstood or these guys are either bandits or crazy or both.
You can get a complete re-manufactured engine including heads for $2,000. here:

http://www.auto-car-engines.com/mitsubishi-montero-1993-parts.html

JackD

I'm perfectly aware that I can get two heads for this car for $100 each from a junk yard, which are guaranteed. And yea, these guys are bandits, I called them and told them not to touch those heads anymore, just do the surface and leave it, they had the same price for the surface like all the other shops fortunately.

I also found a good engine for $600, but I have two cars like this, exactly alike, and the other one will probably need the same work done on it soon. I thought I'd turn this into a lil hobby project, but I'm not getting much positive feedback. I also don't want to abandon this completely, I'm looking forward to putting the car back together.

In either case, once I get the heads back on monday, I'll know which guides need to be replaced for sure. Depending on the difficulty of it I'll decide if I will do it, or put them on the shelf for a time when I have money to rebuild them for the other car while this one gets the two from the junk yard.

I also don't know if it's just me, or if in the States car mechanics are a lot more honest then here in Canada. I have yet to find ONE, that does not try to rip me off from the moment I walk in to his shop.

xp

Finding a decent mechanic is difficult, compounded by the werid phenomenon I see around here where people will both trash talk someone who does good work for them at a good price, and worship the ground of someone who charges 2.5 times LIST price for parts and $100 and hour for labor, while never getting the stinking car fixed right.

Go figure, beats me!

Peter

If your a talented person,

You can replace the valve guides yourself. I've done it and if you are careful- a light lapping and the valves will seat fine.

I would guess your valves and seats probably need grinding though..... On some engines- valves can be found for $2-5 and it's easier than grinding.

While I have not checked lately- Blaines engine supply in dallas use to be dirt cheap on parts... might want to check them out. They were about 20% of the my next closest price when I've done american iron rebuilds.



Michael

Hi samiam4

I was under the impression that valves have to be ground one way or another unless the originals are still in good shape. This should not be a problem. But if it's easier to put in new valves, I don't see a problem with that either.

In any case, thanx so much for the positive feedback.

xp

Got heads back from the shop
 

I picked up both the cylinder heads from the shop degreased and resurfaced. It looks like 4 out of 6 of the exhaust valve guides have dropped considerably. One is chipped from the valve since it dropped so low, no visible damage to the valve itself, the valves don't look worn either, but they are getting checked for specs as we speak.

My dad put together a puller for the valve guides, they are coming out without a problem, I do have a question however.
I will replace the one that is chipped for sure, but as for the other ones that dropped, would there be any risks involved, other then them dropping back down after another 200,000km if I just push them back up, put on new seals and put the head back together?

From the design it appears as if the seal is supposed to hold the guide in place from dropping in addition to it being pressed into the head.

Any suggestions?

Oh, I also heard from a mechanic that you can test the valves for propper seal if you pour gas from the top and watch if it will hold for at least 2 minutes. If the valves hold it, then they seal correctly, anyone ever heard of this method? Is this what is referred to as a leak down test? It just occured to me.

TIA

xp

I guess you could consider it a " partial " leak-down test.
A " real " leak-down test checks the piston ring sealing, as well as the valves, as you are introducing compressed air into the cylinders.
The suggested method of checking the valves/seats with gas, is a new one on me but, considering that you're checking metal-on-metal sealing, it could be correct. ;)

Use water instead of gasoline, it won't catch fire. You could use rubbing alcohol if you want something less viscous that water.

Not a bad idea to check -- there are shops that don't lap the valves in on the assumption that they will "wear in" anyway, and if they are not sealing well enough, the engine is almost impossible to start initially.

Peter

We have used a similar method. We set our head in a parts cleaner and pore some mineral spirits in the chamber (head upside down. WQe then aply air pressure at the head ports and look for bubbles. The bubbles are just easier to judge.

The valve seals provide no assistance to holding the guides in the motor. The spring rotator will peel the seal right off as the guide passes through it into the chamber.

One bit of advice I can give you is that if the guide has moved in the head you can not just put a standard guide back in. For one thing the whole WILL NOT be round anymore if the guide moved. An old tech told me part of my system and we have developed the rest. The original guides are 14.01 and 15.01 OD. The new standard will comes as 14.03 and 15.03. This is a little less than one thousandths of an inch larger. To be sure you get it secure, we get the first over guides at 14.2 and 15.2 mm. We then cut them down on a lathe til they are about .003in greater OD than what came out. With a proper driver we then beat the DS out of them driving them in. They should go in harder than the ones that were not falling out and received the slightly larger guides.

Once in, we put a reamer through to size the inner diameter and its ready for another couple hundred thou.

If your going to machine down some OS valve guides,

I'd make sure your hole is true and no metal was removed. If not, then you want to ream the hole, then machine to fit.

Steve- heat the heat slightly(250F) and cool the guide in a "chill box", the new guides won't be any problem.

Michael

back to the shop
 

I will still probably get these heads back to a shop to get the new valve guides. They will have to be reamed one way or the next.

I'll be calling the dealership tomorrow to find out if this probelm was ever fixed. If not, my dad will come up with something for sure. If not, I'll talk to the mech at the shop to see what his suggestion is. This guy has a good reputation and all the work he does is on tape in case you want to make sure you did not get ripped off.

Thanx for all the advice guys.

Although this car is a domestic piece of crap, you do learn a lot about some things that are in common with many other cars :)

xp