Hello,

I posted here a few months ago about a possible head gasket failure and very rough idle/misfire. Finally took my cylinder heads to a machine shop and.... one of my valve guides and seats broke. Back most intake valve on cylinder 8 seems to have let go from its keepers and dropped into the cylinder, which explains why it was bent when I took the heads off, and definitely explains a rough idle, so maybe I never had a head gasket failure?? Not sure if my thinking here is correct or not.

I have attached a picture of the guide and seat. There are three large cracks in the guide and a part of the seat is chipped off. Machine shop said they would only do a complete rebuild not just the seat and guide for $1900 for both heads, not too bad but to me this is time for more DIY (which is the goal of this project, do as much of it as possible myself to learn). I searched online and 3UZ-FE has press fit valve guides and can be removed. Not sure how I would remove the seat though; since it is already chipped would I be able to carefully hammer it out? As for the valve guide, it seems I would be able to hammer it out from the top down. Has anyone done any of this work before, or know of any good videos/resources for first timers?

For a new valve guide and seat, I just looked up LexusPartsNow and they are sold online. However there are two valve guide options. One is STD and the other is O/S 0.05, which I am guessing means oversized by .05mm. Should I get the standard one? (Screenshot attached)

Also if anyone knows of any good machine shops that can do smaller jobs like a single valve guide and seat near Austin, TX please let me know! Thanks for all the help and look forward to any advice.



Valve Seat Chipped



Valve Guide Cracked


Valve Guide Options (There are two options for valve seats as well but one is continued so leaves me with one option, the standard size)

 

Before you think about attempting this get a hold of the factory service manual so you know exactly what is required. You're going to need a pile of tools and gauges to do the job.

 

Yup already have it all downloaded from toyotas official online manual. Need to look through it and see if they have this process in there. So far I have seen removal and installation of cylinder head and the like but not sure if valve guides would be on there but definitely a good place to check, thank you!

 

Have you tried sourcing replacement heads or even a replacement engine? IMO you should not repair that unless you have no choice and realize there is a greater than 0% chance the repair will fail.

 

I would try to determine why the guide broke in the first place. You don't want this to re-occur.

You use the oversized guide if the bore for the guide is more than what's specified in the FSM. If the bore is out of spec, the bore may need to be reamed to fit the new guide.



You also need to inspect (measure) the valve stem of the valve that's going to be installed in the new guide. It doesn't make sense to install a worn out valve into a new guide. Excessive stem/guide clearance can cause issues at the seat.

As far as the seat goes, there is no replacement instructions in the FSM. However, they're in the parts catalog, but are NLA. An engine parts distributor should be able to come up with a seat insert that will work.

Based on whatever the mileage is on the engine, you might be going down a rabbit hole that ultimately ends up being a rebuilt head.

 

I have looked into a replacement engine about a year ago and the cheapest place that gave a warranty quoted $3,900, which I think would be even more expensive now. Haven't looked into heads, but not sure how much I can trust those, worried a replacement head may have issues and may not come with a warranty.

I am fully prepared for this not to work, for me the risk is worth the reward of being able to rebuild this myself. I studied mechanical engineering, so this really helps me understand clearances, manufacturing technique, and is a super cool project for me. I appreciate your concerns!

 

Got it, will look into it. The engine was already messed with, I believe some sort of top end work was done right before I bought it at 179k miles (it broke down 1-2k miles later) so possibly just incorrect installation of the valve? Will definitely do my due diligence though. For the bent valve, I will be buying an OEM replacement however will inspect it before installing.

I did also find an OEM valve seat on LexusPartsNow, so I should be able to get it through there. Thank you!

 

This is not a task for a DIY. A replacement guide, valve, and seat is not expensive. The tooling required to do it is. The job scope is not very difficult for a machinist, quite simple actually. No machine shop is going to only replace the one guide and install the seat and only cut that. They are going to want to do all that plus a valve job on the cylinder heads, etc. I don't know your location, but whoever told you $1900 to rebuild those heads is ridiculously overpriced. $500-700 is the absolute most it should cost to have a pair of OEM cookie cutter heads done. I would highly recommend you call around to other machine shops in your area.

 

$1900!!?? Wow! You could find a good used 3UZ for half that! and then just do an engine swap over the Thanksgiving weekend. It’d be half the cost, way less work and it’ll be way less hassle than dealing with pulling the heads off, trying keep track off 33 valves and 4 cams and making sure they all get back in the right spot! That could be a real challenge if you haven’t dealt with something like that before.

 

Do you know what tools are needed for a seat replacement? For valve guides it seems pretty simple, might take some time but hammer the old one out and hammer the new one in making sure it goes in straight and the right depth. But will look up other shops, didn't know that quote was on the expensive end of the spectrum. Thank you.

Definitely an option, my only worry is no warranty with those, I doubt anyone would warranty it without installing it themselves. Do you know any good places I can look where I can safely buy an engine that does not have issues? As for the swap, I am doing all this out of a storage unit (where the car is stored) and my apartment, so buying and setting up an engine lift may be a pain to do in a storage facility solo lol. To me it seemed easier to do this bit by bit and put the parts back together, also easier to take breaks when I do not have the time, but replacing an engine would probably need a full weekend IF all goes to plan, and so far things have not always gone to plan so I worry it would take me much longer than I expect to finish. Are there any good videos/resources of someone who has done an engine swap on an LS430? Thank you!

 

I've seen the procedure shown for older Toyota engines (or it might have been Honda) it required boiling the head to a certain temp then extracting the seat. Don't recall the exact tools needed. There isn't a procedure shown by Lexus for this engine AFAIK.

$900-ish per head is not out of line because one needs crack repair etc. the labour time is much more than a normal valve seat and valve grind procedure.

edit - took a quick look at a 1UZ service manual didn't see anything about seat replacement.

 

I have a friend who used to replace valve seats in classic cars so they could use unleaded gas. They had to machine the old seats out, then fit the new hardened seats using heat on the head and cooling the seats, and finally machine the new seats to suit the manufacturers specs. Some really old engines didn't have separate seats and were cast iron, so they had to use a special grinding tool to grind a hollow to fit the seat in.
Replacing a valve guide and seat is not something you can do at home so you are going to be paying someone else who has all the specialist equipment to do it for you.

If this happened to me I'd be replacing the damaged head with a used one. No you won't get a warranty but you won't be paying for one either.
You also need to inspect the piston and bore because to cause that damage to the seat the valve must also have hit the piston and possibly the cylinder wall.
The symptoms will have been similar to a head gasket leak because that impact probably stretched the head bolts allowing the gasket to leak.

 

I would definitely recommend having a machine shop replace the valve seats and then do a valve job to make sure all the valves seat correctly. It’s possible to knock out the old valve seat and replace it but the valve has to be ground to match the seat to ensure a perfect seal. It would be better to get a used head or used engine.
I would look suggest you start watching the local wrecking yards like Pick’N Pull, for vehicles with the right engine to appear on their new inventory list. That will be the least expensive option, you’ll want to find a vehicle that has been wrecked in the rear, or something like that. You can get any V8 from the same generation as your vehicle, either LS, SC, or GS. You could also get a used head from the same place. These engines usually last a very long time, so you be able to source a good one. Make sure to pull the spark plugs out and inspect them for damage, and rotate the crank with a breaker bar to make sure it doesn’t have any rough spots or binding. Do a quick comparison check and if everything seems good, pull it out and take it home. They’ll should include a 30 day exchange guarantee on anything they sell.
Other options would be a JDM importer, but they usually sell the whole engine and trans together and they are usually $2000, but that’ll be for a low mile engine with all accessories including a warranty, so that’s a pretty popular option.
You can borrow most of the special tools you will need from Auto Parts stores, or even equipment rental companies, you can usually rent a cherry picker for $30 a day, and you would just need it for a few days. You could even use a fork lift or something like that if you have access to one. Doing a direct engine swap is not to difficult, you should do any maintenance you can afford before installing the new engine, it’s much easier to do the timing belt and valve cover gaskets etc before you install it.

 

If the guide on the spring side doesn't have a step, a guide driver is used to hammer it out through port side. If there is a step, you have to knock it out the other way. Being the guide is cracked, you won't be able to do that. The guide would have to be machined out to where there is no press to remove it. This is done in a seat and guide machine at a machine shop. The seat gets cut out to remove it. The area where it chipped off would get welded, then machined slightly larger for new seat. You can't install the same size seat that came out. With the new guide and seat installed, the seat then gets a valve job and is cut to a certain depth to where the stem side of the valve has the correct protrusion to have the correct valve train geometry.

Like I said before, this is not a job to do in your garage unfortunately. I speak from experience as an engine builder/machinist. I've fixed more heads from people trying to do it themselves, and they either spend more money for me to fix it than what it would have cost to do it if they would have just brought it in from the start. Or worse, wreck the head to the point they need a new one.

 

I think people need to know their limitations. I will fix almost anything on a car but machine shop work is out of my league because a) I don't have the experience and b) I don't have a full machine shop.