skrappi

06 xB , P0302 misfire. Compression check at shop showed 75psi. All others were in spec. Plug fouled. Replaced plugs and tested injectors. They’re good. Replaced boots on injectors. Because the low psi on #2, shop said it may require rebuild.

my question is, could it be a worn or stuck valve? It’s got 380k miles. Trying all other options first before throwing in the towel. If it’s a value, how can I tell? Can I pull them and have a shop check? I’m fairly handy with a wrench but this would be a first for me.

any and all suggestions welcome. Thanks!

DannoXYZ

Could also be carbon build-up on rings preventing good seal. I fixed a 60-psi cylinder on my wife's Corolla and brought it up to 195-psi to match others with piston soak:

- disconnect all plug wires so engine won't run
- remove #2 plug
- squirt PB-Blaster down plug hole for 5-sec
- gently insert plug back in over hole to prevent evaporation
- let sit for 6-hours
- pour in 2-3cc of ATF
- pour in 2-3cc acetone
- cover and let sit for another 6-hrs

- remove plug from #2, place rag loosely over #2 and crank for 2-3s to blow out excess liquids
- repeat soak-sequence above one more time
- after blowing out excess liquids, squirt in tiny bit of oil and do compression-test

What is compression on #2 now?

skrappi

Thanks for the detailed information and technique. Will definitely give that a try. I’ve also seen a few YouTube videos of people using Marvel Mystery Oil. Considering the age of the vehicle and considerable mileage I may double up and try your suggestion and then try the Marvel Oil. Will I need to change the oil in case it bleeds past the rings and contaminates to engine oil?

Lastly, would it be beneficial to remove the heads to get to the top of the cylinders to scrub out the debris that gets freed up? Not sure if that’s not going to just create more problems or how easy or difficult that would be. Thanks!

DannoXYZ

Marvel is lubrication and can be used for wet compression test. It's just not as good solvent for carbon build-up as PB-blaster, acetone and ATF. Wouldn't hurt to do one pass on its own. Don't mix with others as it'll dilute their cutting power (look up dipole-moment).

No need to remove head as you won't be able to reach into ring-gap, drain holes or inside piston. Which is where deposits are. Stuff on top is superficial and doesn't do anything.

Yes, stuff that's dissolved and freed up is underneath piston and will end up in oil pan. Best to do oil change at very end.

It you want to remove head, might as well drop oil-pan, pull pistons and do full-rebuild:

- drill out & enlarge oil-drain holes in pistons
- new piston rings
- new con-rod bearings
- valve-job

then you'll pretty much have brand-new engine. Don't have to worry about main bearings, they outlast rod-bearings by 3x.

skrappi

Good advice. Question regarding your dropping the oil pan comment, can I pull the pistons that way. I had made the assumption I’d have to pull the motor for a rebuild. If I can w/o pulling motor, I may as well do a rebuild.

DannoXYZ

I recently replaced just rod-bearings on my wife's xB before we sold it when moving. Previous owner was kid who didn't do good maintenance and used cheapo dino oil. Along with letting level get too low. By time oil-pressure light shows on dash, it's really too late. So it got rod-knock about 220K-miles.


You can actually drop oil-pan without removing engine crossmember on this model, we lucked out!

After removing head, you can disconnect con-rod caps and pull pistons and rods out top!

skrappi

Thanks Danno! Good to know. Never did a valve job so if I go that route I had better brush up on my YouTube videos.

skrappi

One thing I noticed when reviewing exploded engine diagrams are the valves are under the cams. I’m unfamiliar with that layout as opposed to a traditional older American built engine. I assume that if I do go the rebuild route the cams an head will need to be removed and head machined by a shop that knows their business. Any links anyone can suggest I can review for the disassembly and process for putting it back together? I’ve done valve repair searches on the sight by only get PCV valve hits. I’m not sure what they are called on this motor.

DannoXYZ

Yes, on DOHC engines, cams act directly on valve-stems through buckets. Much lighter reciprocating weight without pushrods or rocker-arms for more precise control of valves. Less friction with lighter spring. Clearance adjustment is done by measuring gap and adjusting shim-thickness between bucket and valve (cams comes off top). Similar to modern high-performance superbikes, some of which revs to 19,000 RPMs!!!




With modern machinery, there's absolutely zero way you can do as good valve-job by hand using grinding stones. Find shop with Sunnen or Serdi machine that can cut fully-radiused valve-seats. Flows way, way better than stock or even 5 or 7-angle "competition" valve-jobs that used to cost thousand$. Can be done for couple hundred now. Also good to get copper-beryllium seats as they transfer heat much, much faster than stock. Especially helpful if you plan on adding turbo later. One last step after this is cutting flat seat ring for valve-contact. Should be at minimum end of width spec ~1.0mm.




Here's how they're created:

DannoXYZ

Procedure from manual for checking and adjusting valve-clearances. Unfortunately this model engine doesn't use shims under/over buckets for clearance adjustment. You can use spreadsheet to mix-n-match moving buckets around to different locations to adjust clearances. Then end up only having to buy 1 or 2 buckets with thicknesses you don't have. Target larger-end of clearance range since it gets tighter as valves wear into seats.


Some people grind inside of buckets to adjust thickness & clearance. But I can't imagine that's precision operation and would end up with unknown extra clearance over time due to the tips of grinded area compressing down.

RichBinAZ

One way to rule out valve burning is to measure valve clearances. Not that bad of a job.
Inlets should be .006-.010", exhausts .010-.014"
If the bad cylinder measures 0 on an exhaust valve, that will need to be fixed.

skrappi

Thanks RichBinAZ. At the moment I’m still doing the acetone/ATF soak. Giving all four some time to marinate. If I’m lucky that’ll give her some life. If not then I need to learn how to check the valve clearance like you said. Trying anything and everything before I make the call to rebuild.

skrappi

Update: I soaked the cylinders with PB Blaster for 12 hours. (Roughly) followed with an ATF / acetone soak repeated over a few days.

my hope was the ’soak’ would bring the compression back to cylinder #2. The compression check shows #2 still low. I’m assuming it’s time for a rebuild.

that being said, I’ve been able to repair
most things but a rebuild is new for me. I’ve seen comments on this board about rebuilds but some of the terminology is unknown to me as well as the personal experience regarding a rebuild.

can someone please send me a link to a step by step rebuild for this thing? Assume it’s a rebuild for dummies situation.

thanks in advance for any advice or help offered.

RichBinAZ

I thought I may have had a video for a valve clearance check & I do, but it's for the XB mk2. The process is very similar - just different.
The video is a converted slide show, with the slides changing every 5 seconds, so get ready with the pause button (easier on a PC than a phone)

DannoXYZ

It may seem counter-intuitive, but how valve-clearance changes over time is opposite what most people assume. You'd think with wear and tear over time that valve-clearances should increase right? Well, there are multiple areas that wear: cam-lobes, valve-bucket faces, valve-contact area, valve-seat. As it turns out, valve-seat wears out fastest due to high-heat flowing past it and valve continually slamming into it. This causes valve to sit deeper and deeper into valve-seat when closed. This places other end of valve.. the stem... closer to cam! So with wear, valve-clearances actually decreases with wear.

This, along with wider contact-ring and lower-pressure, will cause valve to not seal as well. Thus, can lead to lower compression. Also insufficient seating-pressure and less seating time can fry exhaust valves, leading to even lower compression.

So yeah, measure your valve-clearances.

skrappi

Considering the mileage on this thing, 380,000, would it be just better to replace all the valves, cams and hardware up top and while I’m in there drop the oil pan and manually turn the crank to pull out each piston and replace the pistons and rings? Is that a reasonable way to go? I’m asking because I’m really on the fence if I want to put any time into this considering I have actually never done full rebuild. However since I bought this thing brand new in 2006 I have gotten more out of this car 10 times it’s value easily. Its just been a great car all together so while I’m kind of an amateur Shadetree mechanic to do a timing belt water pump brakes basic electrical and some bodywork, I have never done a rebuild. Considering to take that on but at the same time is it really that involved? As you can tell I’m on the fence between sentimentality about the car and being practical. If was going to be practical I would just sell it for 500 bucks as it is and let some kid rebuild the motor and have a toy to play with

2stroked

If you've never rebuilt an engine before, I personally wouldn't recommend starting with this one - especially if you want to do it without removing the motor. If you really love your car, why not just buy a junkyard motor with far fewer miles on it and swap it in?

skrappi

You’re right. I don’t want this thing turning into a lawn ornament. I’d get stuck on a rebuild disaster.

DannoXYZ

Don't try to do head rebuild yourself, need tonnes of machine-shop tools for these modern engines. Days of hand-cutting valve-seats with grinding-stones and hand-lapping valves are long, long gone! Sure that'll work for crude push-rod engines making 20-bhp/ltr, but when you're pushing 80-bhp/ltr of air-flow through these tiny engines, you need A LOT more precision.

Take head to import shop. They can do really good head-rebuild back to factory-spec for $200-300. Will be brand-new, better than any used item from junkyard. Which should be taken to shop for head rebuild anyway.

When I lived in Santa Barbara, I had all my heads done at place just north in Goleta by airport. Extremely expert workmanship, head-shaving, even at an angle if needed, copper-beryllium seats with those radius cuts. Sometimes, I'd take to another speed shop around corner to have head D-ported and flow-benched as well.