need advice about compression test

[69LC]

So as the title states, I have to do a test on a 4.6 rebuild with 6K on it. It has a terrible miss and seemed to be running on about half of the cylinders the last time I limped it home. I did a search about numbers I should hope to see, but would love any additional wisdom.

I can't really rev the engine as described below as it won't stay running unless I rev it like crazy. Should I rev it for a bit to warm it?

Reviving "the wife's" 80 Last post

Look great to me. Important thing is the numbers are all close to each other, not necessarily to those from another truck.

From another thread:

[/QUOTE]
-warm engine, allows metals to expand, shows you normal operating conditions

-hold throttle wide open while cranking

-crank same length of time for each cylinder

-you are looking for results to be within 10% of each other

-if you have a cylinder that is low, you can put a cap of oil down the plug hole and retest, if the numbers come up to match the other cylinders then you know you have worn piston rings, if the numbers dont' change signifigantly then you have a head gasket or head issue that is the cause of the low compression

-don't worry so much about what the actual #'s are, just that they are close to the same. Different testers, altitude, length of time you cranked over, lots of factors can influence the results so you can't compare them directly to someone else's results with any accuracy.
[/QUOTE]

 

[69LC]

Im really bad at the quote thing...

 

[Irish Reiver]

For what you are looking for I doubt if it matters if the engine is warm or not. Test each cylinder as per your text and see what you get. Main thing is that they are all roughly the same.

 

[69LC]

Thanks. I'll check it out.

-edit: never mind. The crap tester from O'reilly's wouldn't hold pressure. To be continued...

 

[LandCruisinMy93]

Out of curiosity, have the valves been checked for clearance. Valves failing to properly seat will cause a compression loss
that can cause a stumbling engine and poor
Idle conditions. So can wires that weren't connected and sensors that were messed with. Anyway, things to think about if your numbers come up funky (valves) or if they come up fine (electrical and sensors)

 

[69LC]

Ok, for some background-the head was checked and rebuilt about 2000 miles before the bottom end.

The valves were checked by the same shop that did the lower end.

I just bought a compression tester and had these terrible numbers:

1-150lb
2-170lb
3-60ish lb
4-30lb
5-15-20lb
6-30lb

At 4 I tried the oil on the piston trick to see if it would hold more pressure. It didn't.

Am I looking at a bad HG?

 

[ppc]

Have you rechecked 1 and 2 to verify the gauge is working in a consist fashion?

 

[69LC]

Yep...

 

[69LC]

For the time and expense I put into this rebuild I could have done a 5.3.

 

[ccslider]

Try a leak down test. See if it holds whatever number you get for a period of time.

Maybe take valve cover off and verify valves closing.

Good luck

 

[69LC]

Number 5 wouldn't hold. The others held their numbers.

 

[69LC]

I should mention that before I did the bottom end and had the head done, it was .020" out of flat. The shop baked it and then pressure tested it. It supposedly passed.

 

[69LC]

I'm being told I should have pulled the valve cover after 200 miles and retorqued the head bolts. Can anyone verify this?

 

[ajax1]

I have done multiple head jobs and been in on some complete rebuilds. Never had to re torque head bolts after 200 miles. If it wasn't a shop familiar with doing a 1fzfe head maybe they didn't do the 90 degree turns after the book torque of 29 ( off top my head) we would torque to 33 ft lbs then do two 90 degree turns. You do this in a sequence too. If they didn't do that the head could be compromised.

 

[69LC]

I put the head on the block using tech given here. Used new head bolts too.

 

[flintknapper]

I should mention that before I did the bottom end and had the head done, it was .020" out of flat. The shop baked it and then pressure tested it. It supposedly passed.

.020" is quite a bit of warp. I'd want to know where and what direction it was and what their final measurements were after 'straightening'.

Its very easy to over-anneal an aluminum head if you aren't careful. Did they say if the head was warped mainly on the bottom?

If at the top, your cam bores would be seriously out of alignment.

IF the head was not sufficiently straightened (and I'm not saying it wasn't), the chance of having short head gasket life in the future is pretty good.

 

[69LC]

I wished I'd known to ask, but I didn't.

 

[1973Guppie]

I have done multiple head jobs and been in on some complete rebuilds. Never had to re torque head bolts after 200 miles. If it wasn't a shop familiar with doing a 1fzfe head maybe they didn't do the 90 degree turns after the book torque of 29 ( off top my head) we would torque to 33 ft lbs then do two 90 degree turns. You do this in a sequence too. If they didn't do that the head could be compromised.

agree, same here, not necessary IMO.....

 

[scottryana]

Retorquing with stock Toyota stretch to yield head bolts is not an issue. That's a big part of why stretch to yeild are used. There seems to be some arguement (even amongst ARP tech reps) if you need to retorque the ARP studs. I do not think your issue was/is the bolts. It almost looks like the shop who tried to straighten the head decked it slightly tweaked, since your front cylinders show good compression while your rears are poor. Could be a cam issue, did they line hone the cam bores after hearing, bending and machining the deck of the head??

 

[ccslider]

That's why it's always best to get a fsm and not rely on some forum for engine rebuild advice.