Does anyone know the stock head thickness for an 88 4age? Can't find it in my Chilton manual. I read on a website it is 4.568" from factory. I am asking because my head has been surfaced twice. The first time was 10 years ago and I don't know how much they machined off (it has a shim about .030" between the block and head gasket). It was just resurfaced again in my current rebuild another .004". I just measured the thickness as 4.555" (.013" below factory). If that is correct, do I even need a shim at .013"? If I don't add back that .013" thickness with a thicker head gasket, will it affect the timing? Use a MLS head gasket instead of a shim? Thanks in advance. Oh and I don't know the difference between cam timing and ignition timing....if either will be affected.
Stock head thickness?...to shim or not to shim....
1 - 20 of 33 Posts
The 4age is a non-interference motor and the guys on in the MR2 Club use a metal head gasket that is .8 mm thick vs OEM at 1.2 mm to raise compression slightly with no issues but they do warn about it stating only applies to heads that have not be surfaced. I've seen other head gaskets that are as much as 1.6 mm thick for added clearance. The ignition timing "might "have to be tweaked a bit if the compression changes much to avoid detonation (But I doubt it) The cams should be installed the same as they came out.
They mentioned that an un-cut head is 115.9-116 mm thick, so 4.562 to 4.566
Just gotta crunch the numbers.
They mentioned that an un-cut head is 115.9-116 mm thick, so 4.562 to 4.566
Just gotta crunch the numbers.
Thanks, that seems to be what I read on the shim website for the head thickness. So it sounds like the MR2 folks are reducing things slightly without problems or shims. I'm thinking my .013" is minor enough to forego the shim. It's odd that the first machining 10 years ago had a .030 shim in, even though I only have .013 taken off.
I guess the head gasket thickness may have been part of the issue? How thick is the your head gasket when compressed vs. OEM?
Found this on the toymods site.
Re: Thickness of standard 4age gasket VS TRD "The thickness when torqued to spec is 0.8mm on the TRD one and 1.2mm on the stock toyota one."
So .031 vs .047 (oem) when squished!
Found this on the toymods site.
Re: Thickness of standard 4age gasket VS TRD "The thickness when torqued to spec is 0.8mm on the TRD one and 1.2mm on the stock toyota one."
So .031 vs .047 (oem) when squished!
I'm not that familiar with that cylinder head but it might explain why the other spacer was on it from a decade ago.
Is it possible to compress any valves to see how far they open. The head gasket when torqued does give you more room than the piston above the deck. Are those pistons domeed, flat top or have any recess for valve cleareace?
Does your's look like this one?
Also take a look at the 56 second mark on this video and pause it? Spacer or is that a head gasket? Looks like a spacer! Maybe it belongs there and wasn't added last time?
Also take a look at the 8:23 mark on this video, one piston appears to be above the deck!
Is it possible to compress any valves to see how far they open. The head gasket when torqued does give you more room than the piston above the deck. Are those pistons domeed, flat top or have any recess for valve cleareace?
Does your's look like this one?
Also take a look at the 56 second mark on this video and pause it? Spacer or is that a head gasket? Looks like a spacer! Maybe it belongs there and wasn't added last time?
Also take a look at the 8:23 mark on this video, one piston appears to be above the deck!
Attachments
Thanks great vids! Makes me want to do more on this rebuild. That was a head gasket in the first vid, not a spacer. The pistons are the same ones in the pic, D-cup with dishes to allow more room for the valves. I don't think I can compress the valves to see where they land, head is not on yet. From what I know, pistons are flush or slightly below deck from the factory and the "squishgap" is on the high side of acceptable at .047". The Matrix Garage website recommends a min .030" "squishgap" between head and piston if using stock pistons. In my case though, there could have been surfacing done on the block which is why the pistons are slightly above deck. So if I am at .024" above deck, and add their minimum .030" squishgap, I would need a head gasket to be .054" thick. As you mentioned earlier, the Toyota head gaskets are .047", so I am shy by .007", but I am using a Felpro head gasket, so I guess I need to find out what that compressed thickness is. Am I missing anything? .007 is so minimal, but I don't want to make a situation that allows detonation or advanced timing since I have a hunch this car has had that happening with the amount of carbon in it. Any input is helpful.
I wonder if you can contact Felpro and ask them what their head gasket compresses to? I would thing someone would know.
I know what ya mean, I don't even need a motor and going thru this excerise and the video makes me want to build one. If my truck was a 97-98' with the newer ECM I'd being building a new 3.4 with the Supercharger on it since that's legal here in Ca. vs. some other swap like an LS1
i was thinking after seeing those videos, whats so bad about using that shim again? I don't see a down side.
( if it's in good enough condition to do so)
Did see where HKS makes a head gasket that is 1.6 mm ( .062" before torque vs, OEM at 1.2 mm) they don't state squished spec either. Just thinking out loud !
It's a real shame that you have to put everything together to know if it'll all work. I know my son and I were sweating bullets on his Civic engine rebuild, as he went with domed pistons in it. He spent a few days checking into head gasket specs (it IS an interference engine), and couldn't find any reliable info on whether what he had would clear or not (getting Honda engine info is like pulling teeth, nobody wants to share). We finally got to point where we just said the hell with it and put it together. We rolled that engine over several times without it locking up, so we figured we were good. Buttoned it all up, and installed it. Fired it up and it runs sweet. I think we calculated the compression ratio out to be 12.5 or 12.8:1 statically (I've slept since then). I told him he was going to need to run premium gas in it though, as he jumped the compression up into good fuel territory. No more cheap gas for it. He likes the way it pulls now (harder than before). Between the dome pistons, and having it bored the next size up (.5mm) it really woke that little engine up.I know what ya mean, I don't even need a motor and going thru this excerise and the video makes me want to build one. If my truck was a 97-98' with the newer ECM I'd being building a new 3.4 with the Supercharger on it since that's legal here in Ca. vs. some other swap like an LS1
i was thinking after seeing those videos, whats so bad about using that shim again? I don't see a down side.
( if it's in good enough condition to do so)
Did see where HKS makes a head gasket that is 1.6 mm ( .062" before torque vs, OEM at 1.2 mm) they don't state squished spec either. Just thinking out loud !
Thanks for all the suggestions. I've been reading lots of folks unhappy with felpro head gaskets, so I'm not going to use the one that came with my Felpro rebuild kit (all their other gaskets are good though). I'm going to buy one from Cometic (which my machinist recommended). They are expensive, and I also spent money on the felpro one, but at the end of the day, if something goes wrong in the future, I don't want it to be the head gasket and kicking myself. With the Cometic gasket, I can order one to a thickness to take into account any extra thickness I need because of the pistons above deck (they are MLS gaskets). $100 or so but that is cheap compared to the hours of labor going through it again.
I can relate, did that with a airplane engine.
My 1990 Toyota Repair Manual doesn't seem to give the cylinder head thickness. It says if any of the surfaces (bottom, intake, exhaust) are warped past the limit then replace the head. I was once told by a machine shop that if the surface is warped then the top where the camshafts are will be warped too, so even if you surface the bottom the top is still warped.
Why was the head surfaced twice before? Was it warped before or was the surfacing just to clean it, or was it surfaced to increase compression?
Why was the head surfaced twice before? Was it warped before or was the surfacing just to clean it, or was it surfaced to increase compression?
Thanks...my head is at exactly 4.555"....at the limit for surfacing. I think it was only surfaced once before (and this last time at just .004"), and I don't now if it was warped or just machined for surface. It is the block that I'm thinking also had some work done since the pistons sit .024" above deck. I may never know the answer because the shop that worked on it 12 years ago is out of business. That felpro gasket on your chart is the one I have, but that one doesn't take into account engine block surfacing (which I think is why my pistons are slightly above deck). So I'm playing it safe by starting with the .030 min. squish gap recommended by Matrix Garage website (this is based on pistons being level with deck), and then add the .024 for the extra piston height....which puts me at .054 for the compressed head gasket thickness. I don't want to use a separate shim, they add more surfaces for failure, so I'm going to use a MLS head gasket that has the shims built in to it. I'd be curious to know what that felpro gasket compressed thickness is. If it is at least .054" I suppose I could use it.
Yes! I'm putting faith in that Matrix Garage website about the .030 min. squishgap as that is my starting point. They seem to know a lot about pistons so hopefully this will work. Ultimately it is the cylinder running hot condition that I'm trying to get my head around. The first rebuild was due to bad fuel injector burning a hole in the piston. This time around, the rings broke in that same cylinder (I have a thread going about that). It could be a lean condition from something....advanced timing (mine has always been set at 10 degrees) or an air leak somewhere, or I read a bad knock sensor? (so I'm going to look for my knock sensor and check that).
Bad O2 sensor? Which ring broke? What condition is that piston and cylinder in? Did you take a T gage and measure it or hone it? Not sure how much of an overhaul your doing. Timing is correct. Carbon build-up?
Vacuum leak would be lean but I think you would have notice the rpm change or rough idle.
Vacuum leak would be lean but I think you would have notice the rpm change or rough idle.
The way I understand it, he had an issue with oil burning (oil passing the rings) this time. Did the leak down test, and found it was #3 cylinder. Tore the head off, and started to pull the engine apart. Got number 3 out, and found the broken ring (top), then the rest of things that are going on. Originally at some point, an injector failed, and burned a hole in #3 piston (12 years ago). A new piston was sourced, and other work was done, and car was driven about 10K miles until an oil consumption issue. That shop is now closed, and he's doing the work himself this time.
1 - 20 of 33 Posts
