7A-FE engine launched a shim - Toyota Nation Forum : Toyota Car and Truck Forums

Donald · 10-21-2010, 06:22 PM

My car started misfiring a few days ago, so I looked at the usual suspects.
I found oil and dust inside my distributor cap, thought that was it, and cleaned the cap.
It didn't help. I replaced the cap, it didn't help.
I checked the injectors and they are all squirting, so I did a compression check.
#3 had zero compression.

I figured that I had a blown head gasket, and started taking stuff apart.
When I took the valve cover off, I noticed one of the cam lobes at #3 was damaged. On closer inspection, I realized that the shim was missing from the bucket, and the bucket was stuck down (valve open) even though the cam lobe was up. Hence, zero compression!!!

I found about 2/3 of the shim (in two pieces), the rest I guess I'll find tomorrow when I get the cams out.

This engine only has about 14K miles on it since I rebuilt it and did the swap.
I have only hit the rev limiter twice. Once at each of the first two autocrosses I ran with it after the swap, and that was last year. After that I learnt how to use the lower RPM torque curve, and not rev the cuss out of it.
My last autocross was the 10th and this happened this weekend

I'm at a loss as to what would cause this.

Flashmn · 10-22-2010, 07:27 AM

Disassemble it and see if the valve spring is broken, theres not much else that could cause it, unless something went between the cup and the hole in the head where it slides in, thus seizing it. did the valve area have alot of oil in it? Oh and the shim flies out if that happens, as the interference between the edge of the cup and camshaft hold it down in there.

Donald · 10-23-2010, 09:54 AM

I disassembled the head, and from what I see, it looks like the #5 intake shim started comming out, and got wedged between the head and rthe cam lobe. At that point, the cam compressed the shim into the edge of the bucket hole, breaking the shim, and deforming the edge of the hole and the edge of the cam lobe. Broken pieces of the shim then went accross to the exhaust side of the head, and got under the #4 & 5 buckets, breaking the lower skirts of those buckets. The raw edge of the #4 exhaust bucket then chewed up its' hole.
The damaged edge of the #5 intake bucket hole stopped the bucket from comming all the way up, holding that valve open, hence, no compression. The #4 exhaust bucket moved in it's hole but was dragging badly, so the valve would close, but slowly.

The valve springs, keepers and caps all look good. No other damage, other than what I listed, has been detected yet. I'll be examining the cams and their bearing caps to make sure.

I ran a small magnet around inside the gead before cleaning it with brake cleaner, and fished out bits of broken bucket skirt. I haven't found the missing piece (or pieces) of the broken shim

I took the head to a machinist yesterday and he said all I need to do is use a small half-round fine-cut file, then some very fine emory paper, and clean up the holes so the buckets move smoothly in them.

I didn't remember to take the cam with me to see what could be done about that, but I'll be doing some investigating today.

I just happen to have a spare set of 7A shims and buckets.

In this photo, you can see that the shim is missing and the edge of the cam lobe is worn.

Looking from the intake side, you can just barely see the damage at the far right edge of the #5 bucket hole, and the chatter marks in the #4 exhaust hole.

As an aside. I am impressed with how clean the head is inside. I used to use only Castrol GTX, but have used Penzoil for the last few oil changes. The head seems cleaner inside now, than when I did this engine swap last year. The castrol GTX always left an orange/rust coloured deposit.

#5 Intake.

#4 Exhaust.

The shim.

Bucket with broken skirt.

Flashmn · 10-23-2010, 10:25 AM

Yikes, first time I see that.toyota echo has under bucket shims so might wanna see how they would fit, supposedly they should

Donald · 10-23-2010, 10:34 AM

Quote:

Originally Posted by Flashmn

Yikes, first time I see that.toyota echo has under bucket shims so might wanna see how they would fit, supposedly they should

My understanding is that most of the high-reving engines use under-bucket shims.
They started that on motorcycle engines I think.

It is a more secure setup, but more work to swap out shims.
Then again, a Toyota specialist told me that you usually find the need to swap out shims only if the engine has been subjected to high tempreatures for extended periods.

Flashmn · 10-23-2010, 10:52 AM

or you have some other damage or engine work done that changes the valve height.

Donald · 10-24-2010, 02:33 PM

Quote:

Originally Posted by Flashmn

or you have some other damage or engine work done that changes the valve height.

Yeah, agreed.

I found the last piece of shim in the oil pan.

(happy, happy, joy, joy)

Now I can reassemble and not worry about missing pieces floating around inside my engine.

I was starting to stress about that.

Yesterday I visited my local Toyota specialist and showed him the head and cam. He said just do as the machinist said and clean up the holes, and do the same with the cam lobe, so I did. It took a lot of elbow grease before I was satisfied, and now the buckets slide in and out real smooth with no noticeable play. I also replaced the valve stem seals.

This morning I pulled the oil pan to look for the missing piece of shim, and found other metal shavings (pieces of the broken buckets) that I cleaned out.
I also checked and set the valve clearances. I only had to swap out one shim in addition to replacing the broken one although I replaced 3 buckets.

I just took a refreshment break, so now I am going back to install the head.

Donald · 10-24-2010, 02:39 PM

My Toyota guru was also at a loss as to why that shim should commit suciside.
He said that he could only think of over revving as a cause for that to happen, since the valve spring is not broken, but that engine has a rev limiter, so it shouldn't happen.

eage8 · 10-25-2010, 12:54 PM

bad downshift? (ie downshifted into the wrong gear)

Flashmn · 10-25-2010, 01:40 PM

Since its now open, you could take the springs to a machine shop and have them see if they still have proper strength.

Donald · 10-25-2010, 06:54 PM

Quote:

Originally Posted by eage8

bad downshift? (ie downshifted into the wrong gear)

No, none of those.

Quote:

Originally Posted by Flashmn

Since its now open, you could take the springs to a machine shop and have them see if they still have proper strength.

I never thought of that.
Good idea, except that I got it back together this evening.
It runs great.

Funny thing though. When I did this engine swap, I put in 4A-GE pistons in an effort to bump up the compression, and it did, although not by much.
Standard compression reading is 191 psi, and at time of assembly, I got a reading of 205.

In the process of diagnoseing the missfire, I did a compression check and was getting a reading of 240 psi on cylinders 1, 2 and 4. There was some light carbon buildup on the pistons, but it didn't look like it would be enough to account for such great a pressure increase.

Anyway, since I finished late this evening, I plan on doing another compression check tomorrow to see what it now reads since I cleaned the carbon buildup off the pistons.

Maybe my gage is going bad, it is fairly old. I'll borrow one from a neighbour and see how they compare.