'94 3VZ engine valves replacement
#1
'94 3VZ engine valves replacement
Please bear with me, it's my first post, and I'm not much of a mechanic.
I'm the original owner of my 94 Toyota pickup 4x4 with 3VZ engine. I have a small camper on it, and I've been traveling with it through South America. It has 196k miles on it.
A year ago, it overheated and blew a head gasket in southern Chile. We had that repaired at a Toyota dealership; they did not replace the valves.
About 4000 miles later, a mechanic noticed that cylinder #6 had almost no compression, because the exhaust valve had no clearance to close. They machined down the spacer disk, which restored proper compression.
Now, about another 6000 miles later, compression in this cylinder is again down to 50 psi, while the other five read between 130 and 150. The mechanic advises against another adjustment and recommends replacing the valves; this means taking the engine apart again. He says the valves should have been replaced when the engine was apart in Chile a year ago.
Do you agree? I welcome comments and advice. Thanks!
I'm the original owner of my 94 Toyota pickup 4x4 with 3VZ engine. I have a small camper on it, and I've been traveling with it through South America. It has 196k miles on it.
A year ago, it overheated and blew a head gasket in southern Chile. We had that repaired at a Toyota dealership; they did not replace the valves.
About 4000 miles later, a mechanic noticed that cylinder #6 had almost no compression, because the exhaust valve had no clearance to close. They machined down the spacer disk, which restored proper compression.
Now, about another 6000 miles later, compression in this cylinder is again down to 50 psi, while the other five read between 130 and 150. The mechanic advises against another adjustment and recommends replacing the valves; this means taking the engine apart again. He says the valves should have been replaced when the engine was apart in Chile a year ago.
Do you agree? I welcome comments and advice. Thanks!
#2
Registered User
anytime i've done a head gasket, my machinist just checked to make sure the valves were sealing, i wouldn't replace the valves unless there was a problem, the clearances should maybe be checked, low compression could be rings, valves or even a headgasket
#3
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It sounds like you may have a burned valve on cylinder 6....which may be why the mechanic suggested replacing the valves. Now, did the mechanic recommend replacing all valves or just on the problematic cylinder?
Also, I'd be curious to know if the gasket that blew was on the very same cylinder head as #6. Could be why you blew the gasket in the first place.
Also, I'd be curious to know if the gasket that blew was on the very same cylinder head as #6. Could be why you blew the gasket in the first place.
Last edited by thook; 01-04-2017 at 10:06 AM.
#4
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When the valve and or seat wear away enough so that the valve won't full close, the valve starts to burn due to poor cooling and to a blast of hot exhaust gases going past it. That's what happened the first time you had low compression. By changing the shim thickness, you got the valve to seat enough to get the compression back up temporarily, but you still had the partially burned valve, which likely has still been leaking slightly. As before, the hot gases leaking past the valve have now burned it even worse. I suspect your mechanic is correct - you need a new valve.
When the valves are working correctly, the fire in the cylinder is largely burned out and the exhaust gases have cooled to 1500-1700 degrees before the valve opens. When a valve leaks, the gases blowing by are at the full combustion temperature, which is probably upwards of 5000 degrees. Valves don't last long in that environment.
When the valves are working correctly, the fire in the cylinder is largely burned out and the exhaust gases have cooled to 1500-1700 degrees before the valve opens. When a valve leaks, the gases blowing by are at the full combustion temperature, which is probably upwards of 5000 degrees. Valves don't last long in that environment.
#5
Thanks guys, I do appreciate your responses!
The head gasket blew only at cylinder #1 on the 1-3-5 side, the 2-4-6 side stayed intact.
I think we will be replacing all valves; shouldn't we? What about guides and seats? Anything else, while we're in there?
Thanks again!
The head gasket blew only at cylinder #1 on the 1-3-5 side, the 2-4-6 side stayed intact.
I think we will be replacing all valves; shouldn't we? What about guides and seats? Anything else, while we're in there?
Thanks again!
#6
Registered User
I'm concerned about higher compression affecting the bottom end if you do a complete valve replacement. Can a Toyota engine with 196k miles sustain the higher compression of new valves?
bud
bud
#7
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Thanks guys, I do appreciate your responses!
The head gasket blew only at cylinder #1 on the 1-3-5 side, the 2-4-6 side stayed intact.
I think we will be replacing all valves; shouldn't we? What about guides and seats? Anything else, while we're in there?
Thanks again!
The head gasket blew only at cylinder #1 on the 1-3-5 side, the 2-4-6 side stayed intact.
I think we will be replacing all valves; shouldn't we? What about guides and seats? Anything else, while we're in there?
Thanks again!
As for anything else, perhaps your timing belt, pulleys (some of them tend to dry out at around 200k), and water pump. When was the last time those were serviced? Then, there's the wiring/connector from the knock sensor under the lower intake manifold. Those tend to get brittle at high mileage and can cause k.s. signal problems and you can only get to it when the top end is off. What else? PCV valve; cheap and everything will be apart to get to it. Clean the throttle body and maybe a fresh air filter. Plugs, ignition cables, distributor cap, fuel filter? How old are those? These latter items are general maintenance stuff, but still worth looking at if it's been a while. Oh yeah...and injectors! Have yours ever been serviced? The pintle style injectors these engines use are more prone to clogging (than newer style) and sometimes solenoid malfunction around 100k. More so the clogging, for sure, but everything will be apart and that would be a very good idea to go ahead and have them cleaned. And, of course, have all the vacuum lines and coolant hoses thoroughly examined for deterioration.
Anything else, guys?
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#8
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Compression loss due to valves is usually a step function. It goes from normal to almost zero in a pretty short time period. Compression loss due to ring and cylinder wear is a more gradual decline as things wear and blow-by increases. Replacing the valves won't boost ring related compression back up.
Now, if in the process of doing your valve job you mill the head significantly, you will increase compression over factory specs and will indeed increase the stress on the bottom end. For example, shaving .020 off the head will increase the compression ratio on a 3vze from 9.0:1 to about 9.5:1. Could be significant.
#9
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That raises a point I'd thought about when he mentioned the blown gasket. I'd wondered if the head was checked for warping and/or if the head was subsequently milled at that time. Deiter???
ps. Deiter....get them to use new head bolts. The OEM bolts are torque to yield. It's been stated they're not reusable, though I've known people to reuse them. And, sometimes the bolts have failed and sometimes not. I think Ted over at engbldr (a popular toyota parts supplier and service shop around here) even had a video at one time of the bolt heads just popping off while the engine was sitting the shop. Anyhow, worth not messing around with.
Ron....would new valves increase blow by on older rings?
ps. Deiter....get them to use new head bolts. The OEM bolts are torque to yield. It's been stated they're not reusable, though I've known people to reuse them. And, sometimes the bolts have failed and sometimes not. I think Ted over at engbldr (a popular toyota parts supplier and service shop around here) even had a video at one time of the bolt heads just popping off while the engine was sitting the shop. Anyhow, worth not messing around with.
Ron....would new valves increase blow by on older rings?
Last edited by thook; 01-05-2017 at 09:27 AM.
#10
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I wouldn't normally think so, because again, valves usually seal very well until they get a small leak, and then they go south quickly. You likely are not driving around with a bunch of "slightly leaky" valves - there really isn't such a thing as a long term "slow leak" on a valve. It's like a hole in an earthen dam. Once water starts flowing through it, it gets bigger in a hurry.
BTW, this discussion is assuming we're talking about exhaust valves. Intake valves lead a much more sheltered life.
BTW, this discussion is assuming we're talking about exhaust valves. Intake valves lead a much more sheltered life.
#11
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......."Ron....would new valves increase blow by on older rings?".......
Ron, my point, and this question directs the concern to how the existing piston rings will react to new valves that will create higher compression numbers.....I'm not saying the 176k engine will be weak to higher compression, rather asking y'all with more experience with Toyota 3vz.
bud
Ron, my point, and this question directs the concern to how the existing piston rings will react to new valves that will create higher compression numbers.....I'm not saying the 176k engine will be weak to higher compression, rather asking y'all with more experience with Toyota 3vz.
bud
#12
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Apparently I'm not communicating clearly here. My point is that, valves don't cause compression to slowly decrease over the life of the engine. (worn rings will do that.) They don't "gradually" get worse over 50-100,000 miles. They work like new ones until they start leaking, and then very quickly fail and compression drops to near zero. The reason is that they simply can't survive long while leaking - the hot gases and poor cooling quickly eat them up. Replacing the valves simply gets your compression back to where it was before one or more of the valves started leaking. So if the bottom end was good to go before the valves started leaking, it will still be good to go.
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Apparently I'm not communicating clearly here. My point is that, valves don't cause compression to slowly decrease over the life of the engine. (worn rings will do that.) They don't "gradually" get worse over 50-100,000 miles. They work like new ones until they start leaking, and then very quickly fail and compression drops to near zero. The reason is that they simply can't survive long while leaking - the hot gases and poor cooling quickly eat them up. Replacing the valves simply gets your compression back to where it was before one or more of the valves started leaking. So if the bottom end was good to go before the valves started leaking, it will still be good to go.
If you've been running at 75% compression for the last 50,000 miles, the problem is probably not valves, and replacing them won't restore the compression to 100%. On the other hand, if you have 5 cylinders at 75% compression and one that has suddenly (over the last 4-5000 miles) dropped to 20%, just doing a complete valve job (or replacing the valve on the bad cylinder, either way) will likely restore all of them to 75%. You'll have to work on something else to get back to 100%.
#14
Thank you all once again, I'm grateful!
A little more info: After the gasket blew, the heads were checked, found well, and machined down 1/10 mm.
Timing belt is new. Knock sensor, distributor cap, rotor, cables, and coil will be replaced; I assume original Toyota parts are best here. Heading the advice, we'll also replace water and oil pumps; don't know if they've been touched ever...
Yes, this is the exhaust valve in #6 only... so will replacing just it be fine?
Probably forgot something; will read your reponses again.
Thanks much!
A little more info: After the gasket blew, the heads were checked, found well, and machined down 1/10 mm.
Timing belt is new. Knock sensor, distributor cap, rotor, cables, and coil will be replaced; I assume original Toyota parts are best here. Heading the advice, we'll also replace water and oil pumps; don't know if they've been touched ever...
Yes, this is the exhaust valve in #6 only... so will replacing just it be fine?
Probably forgot something; will read your reponses again.
Thanks much!
#15
(Can't seem to edit posts in this forum anymore, so I'll reply to my own).
If you've been running at 75% compression for the last 50,000 miles, the problem is probably not valves, and replacing them won't restore the compression to 100%. On the other hand, if you have 5 cylinders at 75% compression and one that has suddenly (over the last 4-5000 miles) dropped to 20%, just doing a complete valve job (or replacing the valve on the bad cylinder, either way) will likely restore all of them to 75%. You'll have to work on something else to get back to 100%.
If you've been running at 75% compression for the last 50,000 miles, the problem is probably not valves, and replacing them won't restore the compression to 100%. On the other hand, if you have 5 cylinders at 75% compression and one that has suddenly (over the last 4-5000 miles) dropped to 20%, just doing a complete valve job (or replacing the valve on the bad cylinder, either way) will likely restore all of them to 75%. You'll have to work on something else to get back to 100%.
#16
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I wouldn't normally think so, because again, valves usually seal very well until they get a small leak, and then they go south quickly. You likely are not driving around with a bunch of "slightly leaky" valves - there really isn't such a thing as a long term "slow leak" on a valve. It's like a hole in an earthen dam. Once water starts flowing through it, it gets bigger in a hurry.
BTW, this discussion is assuming we're talking about exhaust valves. Intake valves lead a much more sheltered life.
BTW, this discussion is assuming we're talking about exhaust valves. Intake valves lead a much more sheltered life.
now, valves aside, he does have low compression readings on come cylinders. i do suspect rings myself since i assume valve clearances were fine except on 6 when that was discovered.
#17
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#18
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Thank you all once again, I'm grateful!
A little more info: After the gasket blew, the heads were checked, found well, and machined down 1/10 mm.
Timing belt is new. Knock sensor, distributor cap, rotor, cables, and coil will be replaced; I assume original Toyota parts are best here. Heading the advice, we'll also replace water and oil pumps; don't know if they've been touched ever...
Yes, this is the exhaust valve in #6 only... so will replacing just it be fine?
Probably forgot something; will read your reponses again.
Thanks much!
A little more info: After the gasket blew, the heads were checked, found well, and machined down 1/10 mm.
Timing belt is new. Knock sensor, distributor cap, rotor, cables, and coil will be replaced; I assume original Toyota parts are best here. Heading the advice, we'll also replace water and oil pumps; don't know if they've been touched ever...
Yes, this is the exhaust valve in #6 only... so will replacing just it be fine?
Probably forgot something; will read your reponses again.
Thanks much!
also, toyota parts....yeah, if you've got the money, toyota is the quality.
#19
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Compression test numbers can be somewhat misleading, unless reference is made to the altitude above sea level where the test was made.
The 170psi number is ordinarily only possible to achieve very near sea level.
The 170psi number is ordinarily only possible to achieve very near sea level.
#20
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I've read otherwise, but let's that is absolutely true. The bigger factor is compression variance between cylinders, no? Isn't it like no more than a 15psi difference that's considered proper? I think it is. Atleast, to have a well running engine.