Stripped allen head bolt

[DexterH]

Hi everyone,

My name is Dexter and I'm new here and hoping someone can help me with some issues I have with my L300. Particularly 1 issue for now.

I rebuilt my 4d56 engine October 2014. 9 months later my timing belt snapped and broke 2 rockers. I have no idea if the valves are bent and I got all but 2 head bolts slackened out. Those 2 are now rounded on the inside and so I have no clue how to get them out (including without having to take the entire engine out as its the 2 rear bolts).

I have a theory but I have no practical way of testing as I dont have any old heads and valves to work with. This theory is to check for damaged valves. By removing the rocker arm assembly, all valves are supposed to be in properly closed positions which would mean all are supposed to be at one level at the top end. By using a straight edge, placing it at the top of the 1st tappet touching all the way across the top of the others down to the last one, wouldnt a damaged valve be unable to make contact with the straight edge?
Same principle used in checking for a warped head. Can anyone help with this please?

Is there any other way to know if the valves are damaged if i cant get those bolts out? My next idea is to use an old injector (housing) rig up a connection to my air compressor and pressurize the piston chambers one at a time and see if its holding pressure. If it isnt, then certainly a valve/valves are damaged. Again, any help with this is appreciated.

Im not a mechanic, just a guy who enjoys using his hands after spending alot of money at garages and not being satisfied. Now i do it myself once time allows me.

What could possibly have caused a relatively new timing belt to snap considering also the mileage for 9 months is pretty low as well and the vehicle is not used for commercial purposes.
I will give details and answers to whatever questions you may have.

Your help is greatly appreciated.
Thanks guys.

[Lapprentis]

As for stripped bolt removal: go Youtube and you will find answers to this. Other member here will help you for your other questions.

Lapprentis

[DexterH]

Thanks for the tip. Yes I looked through many vids and found some helpful techniques. However my problem is that one of the bolts is located in a recessed area the other is easier to get to. I was hoping someone may have some similar experience as in this situation dealing with stripped boltheads on the engine head itself. I'm fearful of causing more damage to the bolt. How possible is it to weld on a hex key to the bolt and use a socket to remove? Would that heat cause damage to the head?
Ok it may sound like a stupid question but its just 'quick' tack welding. Not allowing the welding lead prolonged contact, so hopfully not allowing excessive heat buildup. Would this still do more harm than good?

Thanks again.

[Growlerbearnz]

That sounds like a nightmare- just thinking about it gives me the shudders.

I wouldn't expect the welding to cause any issues with the head- there's a lot of aluminium around the bolts, which should dissipate the heat from the bolt head pretty well, though I suspect you'll end up needing more than a tack weld. The washers under the bolts are hardened, so if you get that washer too hot you might want to replace it.

I'd be more concerned about weld spatter getting on the valve springs. That wouldn't end well. I would make up a thick cardboard cover for the springs, and dampen it with water. You'll clean all the nice flammable oil out of the head, plug all the drain holes, and protect the valve cover sealing surface, right?

Not sure why your timing belt broke. The balancer belt is still in one piece, right? (The usual thing you find is that someone replaced the timing belt but not the balancer belt, and when the balancer belt breaks it takes the new timing belt with it). Rocker shafts sometimes break, which can jam up the rockers and break a belt, but if your rocker shaft *and* belt are broken it can be tricky to know which one broke first.

I'd recommend replacing the rocker shaft along with the broken rockers, by the way.

[DexterH]

Thanks for your comment. I rebuilt the engine myself after lots of reading and many many videos as well as some guidance from my father-in-law who's been an experienced mechanic in his younger years. He's not too mobile due to health reasons but he's been able to assist when I ran into problems. However, most of the rebuild was trouble free. I was extremely careful in all aspects of the rebuild process and tried to be as precise as was humanly possible. I used most new parts internally, belts, seals, bearings, pistons/rings etc.
The rocker arm however, I reused the old one.

Ok so Im glad to hear that welding is possible and YES I do intend on taking all necessary precaution to keep the welding spatter as limited contact with the aluminium head as possible and everything in it. Definitely a wet cloth or something that wont catch fire too easily. I may be able to get my hands on a piece of fire-retardant fabric to spread across the engine.

Yes the balance shaft belt is intact but thats gonna be replaced as I'm in there. I ended up purchasing a new rocker arm assembly at a cost of just over US$250. I was gonna replace only the broken rockers but when I fitted the new ones on the rocker arm when i went to the store, there was a huge 'play' due to wear. I decided to go with a new rocker arm complete with rockers and was lucky to get the last one.

When the belt broke and the engine stalled, the mistake I made was trying to restart. Thats possibly when the rockers broke. I believe this could have been prevented.
When I had rebuilt the engine, after driving for the first month or so, I never went back in and made adjustments which I'm sure were needed. Possibly the timing needed a one tooth adjustment as the engine broke in and moving parts by this time were properly seated. Even by the second oil change I neglected it due to my time constraints with my job.

So here a l am paying bigtime.

Oh my rocker shaft didnt break, only the rockers on either end did.

I grately appreciate your input and hopefully by weekend I'll attempt the welding method. Can you tell me how to upload pics with my posts? Somehow I cant seem to find the upload button.

Thanks a million!

[Growlerbearnz]

Hmm. Even if your timing is out (or your valve clearances are totally wrong and the springs are binding) I wouldn't expect the belt to break. Rockers, yes- they're supposed to break before the valves get bent.

Pretty sure you'll figure out what caused it once you're inside. Let us know what it was, please!

Adding pictures: there's an "attachments" tab below the post text box (beside "options"). Once you've added a file there should be an option to place it inline, which adds it to your post.

wrecker1.jpg (202.49 KiB) Viewed 6517 times

[DexterH]

Ahhh! Found the attachment button! Thanks. I wondered if thats why the rockers were made from a caste iron type metal compared to the valves which looks like a more tempered type metal. To allow those to break before bending the valves. But I think the valves are possibly bent as I tried restarting after I had stalled.

What do you think about my theory on checking for bent valves using a straight edge across the top of all the tappets?
I have no way to test it as I dont have any old heads to work on. I'm going to try attaching a pic now to show what I mean. Will keep you posted on my findings on the broken belt.

[Growlerbearnz]

Checking the valves with a straightedge sounds perfectly reasonable. Bent valves are less likely than you think, since the valves are vertical- when they hit a piston they get pushed in their normal direction of travel, unlike an inclined valve which gets bent.

That said, any bending is likely to be subtle. I'd probably do a compression test while the cam and rockers are off, jsut to make sure all 4 cylinders are about the same.

[DexterH]

Thanks very much. I'll do that compression test. Man I should've done that before attempting taking the head off. Now I've gone and damaged those 2 bolt heads. Geeez!

[DexterH]

Hey folks! Its been a long afternoon working on those bolt heads but after 3 and a half hours they were finally out.

I soaked a few pieces of cloth in water and covered the areas over the head where welding was to be done.

First attempt fitting an allen key (straight piece about 1" long) into the head of the allen bolt and welding it, did not work. Allowed it to cool before using a 10mm socket and breaker bar, but the allen key ripped off just above the welded spot.

Second attempt, I used a 17mm bolt and carefully welded that onto the allen bolt. I was sure to give it a good weld, at least I thought I did. Again, that bolt broke off as well.

The entire process took long because I had to constantly monitor the entire engine area for any sign of fire. There was slight damage to the insulation on the fire wall. I didnt have a piece of metal sheeting to stick between there, so I soaked it with water and that helped.

Ok so my third attempt, I used a lug nut and placed that ontop the allen bolt. I tack welded the inside first and then tapped the lug nut in proper position. Once I got it straight as possible, I continued to weld around it as well as filled the inside of the lug ensuring it was properly fused with the head bolt. The entire nut was glowing red hot.

Allowed it to cool about 15 minutes and it took quite a bit of force, but I soon heard that crack of the bolt indicating my success.

I took the bolts out and noticed metal filings on the threads. I think its possibly from the machine work I did on the block last year, or the head. Could this have caused the bolts to lock into the block?? I saw the same filings on the threads of the second bolt as well.

Good news is the valves didnt look damage after pulling the head off, but Im still gonna take it apart and clean out all the flux and spatter from the welding. Definitely some grinding just to make sure the valves seats properly.

I do have my suspicians about why the timing belt broke. Considering how badly worn my rockers/rocker arm was when I compared it to the new one, I think a rocker must have broken and jammed under the cam shaft and thats what caused the timing belt to snap. When I first took the tappet cover off, I didnt think much of it then, but since Ive been pondering on it past few days I do remember the back piece of one of the broken rockers was stuck just under the cam.

This had to be the culprit!

I welcome your thoughts, anyone. Im faced with another challenge tomorrow. The crank pulley bolt. Now that the head is off completely, can I still use the starter method? Chuck the breaker bar, with socket on the crank pulley bolt and give it a tumble. Should still work right?

Its gonna be a long Sunday folks. Wish me luck!

Dex

[Growlerbearnz]

Glad you got the bolts out! The metal shavings in the threads are a worry, apart from causing the bolts to bind they would also mess up your torque settings when tightening the head bolts. It might be a good idea to clean out the bolt holes with compressed air and run a tap down them to clean up the threads.

[DexterH]

Took apart my compressor to rebuild the head a few months ago. Alot of corrosion built up after it been down for a while. Never had time to get back on it.

Darn! Now I need it!
Talk about 'head' aches,huh!

I'll do my best to clean those threads.

Thanks GrowlerB