420A Help with damaged spark plug

[Cypherfox]

I would like advice or direction to get my car fixed properly.
These are parts that I replaced and not updated on my profile -spark plugs (ngk IX Iridium 6418) and Duralast gold wire set. The care ran with no noticeable changes. Two days later I was driving on the highway (idling at 55mph) when the car just shut off. I did not hear any noises nor was there any smoke coming from the engine. I pulled over and tried cranking the engine and it would not start. I had it towed home and started looking for the problem. The car cranks flowly but will not start. I pulled the sparked plugs and saw that cylinder four had major damage to the electrode. What should I do to diagnose this problem? I'm thinking I should pull the valve cover and engine head assembly, check timing belt and components, have a machine shop check the head for damage, reassemble if everything is okay.

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[JeffGS-T97]

I finally have the engine and transmission removed. I was able to lift them both out as one complete assembly. The two bolts that I couldn’t remove at the beginning stayed on the engine. I forgot about them and just focused on the removing everything else. I’m going to secure the engine on a stand soon and hopefully figure out why the spark plug was damaged. Thanks for all the replies.

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Nice work and progress man. My favorite is the next step putting new goods in the engine and bringing it back to life

 

[Cypherfox]

Nice work and progress man. My favorite is the next step putting new goods in the engine and bringing it back to life

Definitely! I can’t wait to drive it

 

[jpmxrider489]

Something that happened to me, I had a valve spring fail and damaged my spark plug. Similar to yours. I also broke a valve. Just sharing my experience.

 

[Cypherfox]

This is the hardware I used to mount my 420a engine on a engine stand. I hope it helps someone that is looking for which bolts to use.
*corrected mm to cm on the picture with blue stand arm. Thanks Deric for letting me know.

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[Dericsh]

This is the hardware I used to mount my 420a engine on a engine stand. I hope it helps someone that is looking for which bolts to use.

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Is the mm bolt length measurement suppose to be cm?

 

[Cypherfox]

Is the mm bolt length measurement suppose to be cm?

Yes I will correct it. Thanks for pointing that out.

 

[BLACK'98DSM]

That's useful info, thanks for sharing! I remember my belhousing bolts being too short to use.

 

[Cypherfox]

Update and looking for advice

My now is to buy a engine from a Junkyard so I can have a way to get around. Im going to take my time rebuilding the one that is damaged.

This is where I’m at right now with finding out what happened inside the engine. I got the crank pulley and the timing cover removed. I found can see damaged parts looking inside the intake ports. Should I still try to put timing on TDC? I’ll include pictures of what I see.

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[dustyboner]

no that the head of the valve that broke off.

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pull the head off and see if the cylinder walls and the head are fuct beyond repair.

 

[steve]

Sadly, something like this is what I expected when I saw that spark plug but didn't want to rain on the parade.

 

[97egl]

My now is to buy a engine from a Junkyard so I can have a way to get around. Im going to take my time rebuilding the one that is damaged.

If at all possible put a timing belt on the junkyard engine before you put it in the car. I know you said you need it to get around so another day putting a timing belt on isn't ideal but I've seen so many people break belts and go get a junkyard motor only to have that belt break.

 

[Cypherfox]

Update
I removed the cylinder head and found major damage. The camshaft journals are scored and bearing caps. I think the valve from cylinder one broke off and ended up in cylinder three. I think it’s odd because it didn’t hear any noise when the car broke down. I feel like I need someone that has the tools and knowledge to help me out further.

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[Cypherfox]

It took a lot of work, time, money, learning to get to this point.

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[waltah]

It took a lot of work, time, money, learning to get to this point.

And all your readers thank you for taking the trouble to keep us in the loop!

Possibly the timing belt jumped a couple (or more?) teeth so the valve hit that piston. The broken valve head proceeded to do the rest of the damage. Either that or some foreign object got in there broke the valve and went away. Probably could get that running without an air filter if near wide open throttle.

Looking at the broken stump on the valve (in your picture) you can see it was bent dramatically to one side before it broke off.

How was the valve timing and timing belt when you pulled it apart? Probably the belt was broken so no real info there.

Gee, reading your posts I don't have the feeling you need someone else to help you other than by advice when you post info and questions. My first question --- I've never had an engine go this far wrong (well, except for that VW back in the 70's ...) -- my first question would be what is salvageable? The head, cams, and pistons appear to be trash. Someone with a lot more experience might be able to say something about the block and crank: If the cylinder walls are okay then the questions would be something bent or cracked down below I guess.

A good machinist would be able to advise you but my instinct would be find another used-but-running engine to rebuild just because a good rebuild is such a big deal and you'd hate to get to the end and have it crap out in 100 miles.

 

[BLACK'98DSM]

If you're going to re-use the current engine, it's going to need a full overhaul.

I would not re-use the cylinder head, since the cam caps are worn and there's damage to the combustion chamber. Find a replacement head. It is repairable but there is no lack of 420a cylinder heads so take the easy route.

Unless you buy a new or remanufactured cylinder head, the replacement will need work. It will need to be shaved to ensure flatness so the head gasket can seal. The valves will also need to be lapped to ensure no compression loss and the valve stem seals will need to be replaced to ensure no oil consumption. The cam caps and journals will possibly need to be machined. All of this can be done at a machine shop. I usually give them the new valve stem seals and the head assembly and they sort out the rest.

Your head bolts are stretched. You need new ones, not used. They are torque to yield. Some will say you can reuse them if you measure and they're not too stretched. But blown head gaskets on fresh rebuilds are not fun. Buy new ones and be safe.

I would imagine the cylinder walls have major vertical scoring. Probably not something that could be honed out. At a minimum I would bore 20 over, just a guess without seeing. 40 over wouldn't hurt. You're obviously going to need new pistons and rings. Buy the correct size per boring specs.

The block also needs to be shaved to ensure the head gasket will seal. Some will just clean the mating surface and call it done. But once again, do it right and be safe. The machine shop can do this. They usually dip it in the hot tank to clean the gunk out if the oil and coolant passages as well.

Cams are damaged, get replacements. Since those are damaged I would imagine the rocker arms and lifters are damaged as well. Hopefully you can find some of these items with the replacement cylinder head. Rocker arms and lifters are fairly cheap brand new if not.

Your timing belt is garbage. This is a great time to do the full timing job. Including belt, both idler pulleys, tensioner & pulley, water pump, oil pump. Oil pump is optional but because of the top end wear I'd be safe and replace it. The main seal is probably going out anyway.

For the crankshaft, you may not be able to visually tell if it needs work. It might be obviously damaged. If not, numbers speak louder than looks. The journals need to be measured with a micrometer to see if they're still within specs. If they are within spec but you can see damage or scratches caught by fingernail, at a minimum the journals need to be polished. If larger damage, have the journals machined down and get oversized rod bearings, usually 10 over. Do the same for the main bearings.

The rods can usually be re-used. But check the one with cylinder damage. Make sure it didn't get bent or cracked when the valve smashing occurred.

Obviously all new seals and gaskets are a good idea since the old ones will already be removed.

If you need pointers on the break-in period of a fresh engine I can help there as well.

If you're going to tackle this whole job yourself, ask away with all of your questions. There are a lot of things that need to be done right or the result could be detrimental. Don't let this intimidate you though. The 420a is not a very advanced engine and I find them fun to rebuild. If I can do it, you can too.