Stuck Exhaust Lifter


4 replies to this topic
  • Maximus_Manimal

Posted July 16, 2012 - 09:55 AM

#1

Just getting back into dirt bikes after a decade long hiatus (wreck, marriage, kids, etc). The last thing I wanted was some project bike that would consume every weekend because I'd spend more time working on it than riding it. Sadly, that seems to be exactly what I bought.

I recently picked up a '98 YZ400F for $1200. Was one hell of a bike... for about 2 hours. While on a family outing yesterday, we stopped for lunch and I suddenly couldn't get it started. It felt like I'd lost all compression. I could roll the motor over by hand.

We broke out the tools and the trail fix ideas started being thrown everywhere, but none of them panned out. The decompression cable/lever was not stuck, nor was it improperly adjusted. The decompression pin actuated smoothly. At this point I'm thinking a cracked valve or head, lost head gasket, or even rings in the bottom end.

I get it home last night and pull the valve cover off and figured I'd measure valve clearances before going any further. That's when I noticed the right exhaust lifter was about 1/8 inch below where it should have been. Pulled the exhaust cam to verify, and sure enough that lifter is stuck with the valve just barely in the open position.

Looking closer I could see a small burr on the decompression pin where it would make contact with the lifter. I figured it had flared or mushroomed out the top of that lifter and it had mildly galled the bore it rides in, and had now become stuck. I don't think this is a terribly difficult problem to solve. I have already removed the burr from the decompression pin and polished the flat and curved edges to prevent future occurrences, but now my attention turns to removing the stuck lifter and assessing the damage done to the bore.

I cannot for the life of me get that thing out. I was able to get it to pop up to full height position by heating the head from the outside (expanding the aluminum and allowing the valve spring to push it up), but with nothing to grab onto the only way I can think of to get it out is a stick magnet. The only one I had at the time wasn't nearly strong enough to get the job done.

I have some very strong rare earth magnets at work (Neodymium I believe) but after noting that it was stuck bad enough that the valve spring couldn't move it, I'm not very convinced that one of these super strong magnets will get me any further.

Anyone have any other thoughts? How can I get this thing out? Maybe cleaning the top of the lifter and using duct tape as an adhesive handle in conjunction with the stronger magnet (two types of coupling mechanisms basically)? I'm worried about doinking the head and earning myself a whole top end project (the wife will LOVE that, I'm sure).

  • grayracer513

Posted July 16, 2012 - 11:53 AM

#2

One thing you can try once you get the lifter freed up a little is tapping on it sharply with a punch sop as to bounce it against the valve spring and have it bounce back up. If you can get it to stand over the cam bore, you can grab it and pull it free.

What I ended up doing once was to find a tower nut and a piece of rod I could screw onto a slide hammer and then tack the rod to the top of the damaged lifter with a MIG welder. Then I pulled it out with the slide hammer.

The head will probably need some repairs to the lifter bore. Engine Dynamics can do that kind of work at a reasonable price.

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  • KJ790

Posted July 17, 2012 - 02:34 AM

#3

I'm with Gray on this. I once had to weld a bolt to the top of a lifter and use a slide hammer to get it out. I used a piece of tin roled into a short tube to protect the bore of the head while welding. Once I got the lifter out I had to have the bore repaired (my lifter had cracked during an engine failure, which caused it to wedge in the bore). This method worked pretty well.

You also may want to make sure that your valve is not bent, which could be another reason why the valve is stuck open.

  • Maximus_Manimal

Posted July 17, 2012 - 09:12 AM

#4

Alright, well last night was eventful. I tried the strong magnet (with roughly 5-6 lbs of force), and the magnet with duct tape and heating the cylinder. Nothing worked. So I moved on to plan B, namely welding a handle to the lifter. I had two primary concerns. (1) The only welder I have is SMAW (a.k.a. "Stick") so naturally slag deposition was a big deal. (2) Stick welding has a tendency to heat the work a lot more than other methods, and as such I was concerned about the lifter expanding so much that it applied enough force to crack the head.

To address concern 1, I used the fore mentioned duct tape to mask off every port, valley, journal, or otherwise exposed piece of metal not to be welded. Splatter was also on my mind since the cap had lived its life in oil, so it received a good cleaning with brake cleaner. Next, I broke out the smallest 6011 rod I had (3/32), which also happened to have the least amount of flux surrounding the filler. To address concern 2, I had a spray bottle of water right next to me and I was going to make the weld in 2-3 short tacks. I decided to weld a nut to the lifter rather than a bolt, primarily for ease of holding it in place and I could use different length bolts if needed. Also thought I'd mention I removed all electronics from the bike before this (since someone will inevitably try to bash my head in with this if I don't say it).

After psyching myself out, practicing the actual weld a few times on scrap, and making sure I had a contingency plan if I really messed up I went ahead and did it. The first thing I noticed is that because I had to move the grounding clamp further from the work than I had practiced, the extra resistance made my settings too cool. After a slight tweak in current, I made the first weld. The bead was a little larger than I wanted, but I was able to complete it without any problems. After allowing it to cool for several minutes, I went for the second tack. This one went much better, and I felt that was good enough.

I allowed the second weld to cool, screwed in the bolt and after a few good taps with a brass punch out she came.

Posted Image

In this second image you can see the offending decompression pin impact marks which caused the galling. If you see something similar (meaning near the edge like mine) I highly recommend attacking the problem before your lifter gets stuck this bad.

Posted Image

There just HAPPENED to be a gentleman within 5 miles parting out a 99 YZ400F and I was able to pick up all 5 lifters for $35. Here's a picture of the "new" lifter which also has decompression pin marks in its surface. Notice these marks are inside the face, and not on the edge. I will keep an eye on this, and if it appears to be heading the same way I will actually dish the back part of the decompression pin so it can only contact on the face of the lifter.

Posted Image

Now my attention turned to repairing the head itself. I cleaned out the flux and carbon deposits (must not have gotten all the oil out, also the duct tape caught fire for a second) and removed all my masking material. I called around to several local machine shops, none of which were willing to do this work. I called South Valley Motor Sports in Draper UT (not quite local, but worth the drive if it saves me shipping) and they quoted me $290, and also said they'd have to ship it out. I contacted Engine Dynamics, who quoted me $175 and also said they were swamped with at least a 3 week lead time. To be fair, this was a quote without seeing the damage so it could have been less, but by the time I have a realistic quote I'm already committed to paying for shipping twice.

Not liking any of these options, I sat back and reflected on my redneck roots. I could see the damaged area in the bore and it was pretty minor. There was a slight ridge (which I could not get a decent focused image of) about half way down the bore, and the rest was nearly untouched. After a few minutes I thought of a brake cylinder hone. It'd be about the right size, and if I were to proceed with caution it just might work.

I ran out for parts (valve compression tool, cylinder gasket set, small hone) and after spending another $87 I was ready to disassemble and try it. Because the hones were brand new they were a little coarser than I would have preferred. As such I wanted to practice the procedure first. I used the spark plug hole as a proxy, and I'm glad I did. The hone started a little rough at first, but some of the crap that inevitably accumulates in an occasionally open hole like that quickly filled much of the pore space in the hones, effectively making them a finer grit. After a few seconds in that spark plug bore, I had removed about 0.002" and the surface was nearly perfectly polished.

I cautiously moved to the lifter bore, and away I went. Again, I measured the bore before and after and didn't end up removing quite as much material (I was being pretty conservative) and it was about 0.0015". The ridge was completely removed and the galling was almost completely gone. The few small marks that remained were discontinuous and were inside the bore (meaning I could not measure a positive material displacement over the top of them) so I stopped there. It looked almost new again. I cleaned the bore out really well, coated the new lifter in oil and it slid beautifully in and out with no more play than the same lifter in adjacent bores. I didn't get pictures because by this time it was pretty late and I was too focused on the problem at hand.

I proceeded to thoroughly clean every part of the head and valves, reassembled the head and installed with the new gaskets. Got the cams back in and rolled it over and everything was moving beautifully. So NOW I could finally measure my valve clearances. All of the intake valves were out of spec (by a fair margin, but not dangerous), and both exhaust valves were right on the low edge so I figured I'd do them anyway. I had measured the valve shims when I had everything apart, so I was able to pick up the new shims this morning and should have it all back together and hopefully fire it up tonight.

Thanks for your input, and if you have a 400 or 426 without an auto-decompression cam I'd recommend checking the top of that right exhaust lifter next time you're in there just to make sure. I can supply pictures or drawings of the pin if there is interest.

  • Maximus_Manimal

Posted July 18, 2012 - 01:03 PM

#5

I got it all put back together last night, and after double and triple checking everything I kicked it over. I'll be damned if it didn't start on the first kick cold! It has NEVER done that (you know, in the two weeks that I've had it). After checking oil and such, it ran like a champ. I'm looking forward to getting this thing out again, though staying within walking distance of the truck until she's proven herself a little better.

Also, after a little consideration I decided to modify the decompression pin anyway and head off any potential for future damage. Ideally I would have preferred a full on replacement exhaust cam with auto-decompression, but it's simply not in the budget right now. The mod was minor and could be done simply by pulling the pin if you knew exactly how far to grind on that edge.

Edited by Maximus_Manimal, July 18, 2012 - 01:12 PM.






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