Valve compression question

[vtchris]

What is normal compression? 1991 V6 3.0 with 107K and compression on one cylinder is 180 and on another 120, I will be getting the others done soon. Mechanic thinks I need a valve job. My CEL is on and gas consumption up 20%.

[Derek up North]

!80 & 120 is not a good sign. The actual value isn't too critical since there are many variables that can change them in the same engine. Generally, a healthy engine will be 150-180psig. I don't think a Toyota V6 will be much different. What is important is that they all be close. The value generally given is 'within 10%'. So if you've got 1 at 180, none of the others should be less than 162-165psig.

Have you managed to find a good mechanic? I can't say I've ever come across a mechanic who tests only 2 out of 6 cylinders. When you go back, make sure that all 6 are done in the same session.

Before giving the OK to do any major work, you've got to make sure the compression test is done properly and if you still get results like that, get a 'Leak Down Test' done. That'll give you a more accurate picture of what's going on.

http://www.google.ca...GGLL_en___CA408

[vtchris]

The mechanic was too busy to check the others, he had already spent half an hour with me and I was just a drop in. I am going back tomorrow and will ask him about the leak down test, thanks. Anything else?

[Derek up North]

Just watch his reaction to a 'leak down test' suggestion. If it doesn't look like he knows what one is or isn't equipped to do one, try and find someone who can.

And when he's doing the compression test, ask if he's going to do it with the engine warmed up and with a 'wide open throttle'. Even if you don't understand, watch his reaction to see if he does! Also, ask if he'll do the compression test 'dry' and then 'wet'. 'Dry' means he checks it 'as driven in'. Then for a 'wet' test they add a little oil in each cylinder. If you're losing pressure past the piston rings, the pressures should rise a bit/lot as the oil will seal up the rings. If 'wet' doesn't improve things, then the pressure is being lost elsewhere, either up the valve stems, leaky valves or bad head gasket.

Another thing (important) is to get a copy of the results.

Let us know what you find out.

[vtchris]

An independent mechanic who seems to know what he is talking about did a compression test today and says I have a burnt valve (30) on #6 as compared to 180 on the others, except for #3 which had 120. He is going to do a valve job, new lifters, head set and bolts for $2500, quoted 21 hrs labor. He said no need to do leak down test (he definitely knew what I was talking about). He did the test full throttle with all plugs out. Said it won't necessarily fix the CEL, but this needs to get done ASAP....like I shouldn't even drive it. I will pay for the parts tomorrow and take it to him on Monday and camp in his parking lot until finished.

[Tom W]

Their is a lot of labor for this job,the lifters usually don't need replacement their not hydraulic they have a shim for adjustment usually when they do the heads in a machine shop they cut the ends of the stems to match the old shims which don't wear much they are very hard metal.

There will be other things that show up exhaust manifolds warp and can be machined not to costly, the timing belt has to be removed might as well replace it if there's some mileage on it, if its original its over due anyway. Piston rings on this eng if it hasn't been run hot are probably still ok. Some of the v6's had a head gasket problem so get quality gaskets Toyota says that the head bolts don't need to be replaced

when reinstalling heads but probably is a good thing to do, they use degrees to torque them it would be a lot of torque.