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Mazda 2.0L \  Black crud in last two head bolts

Black crud in last two head bolts

Mazda 2.0L Mazda Engine Mazda Tech
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replies 38
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rooftoplounge   +1y
Hey all,

I have an 84 B2000, 137K. Lost compression in cylinders 1&2, suspected possible head gasket. As I was pulling the last two head bolts at the very back of the engine I saw there was a bunch of hard, black crud mixed in with the oil. I take it that this isn't normal but the stuff was only on the last two head bolts, not on any of the others... What could that be?

The head gasket was busted right between the cylinders 1&2, I'm assuming that was the culprit to the compression loss. Is it possible to check for bad rod bearings and/or rods without pulling the oil pan or should I go ahead and check everything while most of the engine is broken down? Thanks in advance!
sincitylocal   +1y
That's coked oil. It got hot back there a time or two.
If it were mine, I wouldn't mess with the bottom end unless you're thinking about replacing the rings to eliminate oil smoke/burn.
rooftoplounge   +1y
Thanks SinCity! I appreciate the reply. I never noticed it smoking very much when I drove it but the cylinders looked pretty glazed with odd liter "scuff" marks toward the bottom of them. I couldn't feel anything when running my finger over them tho.

I did notice a pinging sound when I would put a load on the engine while going up-hill, could that be rod knock or is that a symptom of blowing the head gasket? I'll take pics of the head and cylinders tomorrow and post them.

Thanks again!
sincitylocal   +1y
Try a higher grade fuel for testing. If the ping goes away, your timing is a little too far advanced.
rooftoplounge   +1y
I've included a link of a couple of pics of the head below. Wasn't too difficult, just a bit of a pain to get the EGR pipes and discombobulate the vacuum hoses. I'd like to eliminate them all together. I've looked at some of the other posts about doing this but having to completely change the carb to a Weber. Do you know off-hand if it's possible to plug all the vacuum lines keep the original carb or would I be asking for more of a headache?

Thank you for the suggestion to change up the gas!

befarrer   +1y
You could possibly plug all of the vacuum lines, but your fuel mileage will be in the toilet, power will be down, driveability will be crap, and generally everything will we much worse than any carb can ever be lol. It's an electronically controlled carb, and it uses the mass of vacuum lines to control it correctly, and if they are all disconnected, it goes into a failsafe mode, which means dump as much fuel as possible into motor mode.
rooftoplounge   +1y
Thanks befaarer! I'm putting it all back together but I'm having issues with figuring out the timing. I have cyl #1 at TDC but I pulled the cam sprocket from the chain while wiping down/inspecting parts and I don't know what position the cam should be in.

I don't think the chain slipped around the crank sprocket and I see the two "plated" links in the chain. How would I proceed? Thanks again all!
rooftoplounge   +1y
Why in the world is it so difficult to find timing info on the earlier b2000s? Spent half the day scratching my head, reading the chiltons and the other half online searching. Am I the only one finding this difficult or did I go about this A$$-backward?

Is the best way to be sure the timing is right is to take off the whole front face of the engine (water pump and all) so I can see plated links of both the crank and the cam? Is it best to loosen the chain tensioner before trying to slide the cam sprocket onto the keyed slot of the cam?

The cam sprocket has an arrow on the face of outer most ring and then has a 4 on the next ring in. Does the 4 mean anything?

-sigh- why do I love my little red truck so much...
rooftoplounge   +1y
Hey All,

I've hit a bump in the road. I'm trying to assess where the timing mark is for the crank sprocket. I am looking to pull the front cover off but the pulley mounting flange is in the way. Does the long bolt going into the pulley come unscrew? If so, how? and how do I hold the crank still? How do I get the timing chain tensioner back in and keep the pushrod held in?

My Chiltons does NOT cover very much in detail and I'm trying to piece together what I can online and in the manual... Thanks for the help guys!
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befarrer   +1y
That front bolt looks to be simmilar to the rotary one, which comes unscrewed and the pulley flange comes off. I remove mine by putting the truck in 5th gear, putting the e-brake on as tight as possible and use mr. long breaker bar. It's probably never been off, so it will be stuck on good.