The Trouble with Tappets

Last week I opened the heads on my Honda PC800 to replace the cam plugs.  It is a relatively straight-forward job.  However, there are three tappets per cylinder that can cause some problems.  Sometimes the tappets won’t release from the head cover until it is in just the right position for a tappet or tappet shim to fall into the engine.  That happened to me.  Or I thought it did.  The missing tappet surfaced after I started hammering on the oil filter with a screwdriver to get it to come loose.

I thought I was in the clear but then after I reassembled the heads I discovered an extra tappet shim!  This could be a problem but I’m not entirely sure.  I reassembled the engine enough to listen for any bad noises.  The video below is what it sounds like now.  What do you think? Am I in the clear or do I need to rip apart the heads to check tappet height?

This is when I had the back head cover off.

This is the bike together enough so I can try firing it up. It took about two or three minutes of cranking and recharging the battery with the trickle charger for life to come back to the PC800.

18 Replies to “The Trouble with Tappets”

  1. Sweet merciful crap. That’s just terrifying. I’ve read lots of posts about replacing the cam plugs, but I have no idea what they are, what they do, or where they’re located. Should I be worried about this?
    -Frightened of Icky Engine Parts in Hershey

    1. Don’t worry, Scott! It’s not that bad. Had I not been working in a poorly lit space between two buildings under a blue plastic tarp at night, I probably would have not had that problem. I’ve put 3 or 4k miles on the bike since reassembly. No problems yet! The extra tappet shim is sitting in my living room on the book case. It servers as a warning to the other tappet shims in case they get uppity 🙂

      The biggest tip I can give is to go SLOWWWWW with removing the head covers. I didn’t fully appreciate that there were three metal tappets about the size of pencils that would stick to the head covers and not stay in the heads. I couldn’t see them very well with the lighting that I had so I assumed they were still with the main engine body. I was wrong!

      Also don’t forget that at the bottom of each tappet there is a tappet shim or two. Each is specific to that tappet (supposedly although my bike says otherwise). The best policy is to keep the tappets and their shims in the head rather than letting them pull out. In retrospect, the way that I should have done it was have an assistant help me slowly pull each head cover up to about 3/4″ above the head and then stick some pre-cut blocks of wood or wedges of wood in between the head cover and head. Then get in there with fingers or a tool with very VERY soft grippers to gently pry the tappets down into their proper holes. The only three bits of metal that should be connecting the head and the head cover will be the tappets. Then next raise the head cover a bit more, check again, etc, until the head cover is in the clear.

      SLOW AND STEADY WINS THE RACE. Don’t be like me (some hot-shot young kid) and nearly give yourself a heart attack when you first hear *plink plink plink* as a tappet disappears into the bike (it shook loose later from around the back tire. No clue how it got there!). Also don’t give yourself a second heart attack when you find an extra tappet shim laying on the ground under the bike after it’s all back together. Both are bad news.

      Otherwise as far as the cam plug job is concerned, it’s not too hard to do. Takes a day to get everything off and put everything back on. You should order new radiator hoses for the water pipes while you’re at it. I had to wait a month for new ones because my old ones were in such sorry shape.

      Good luck Scott! And if you’re too scared to do it, I plan to be out your way in a year or two once I finish my degree. I’d be happy to make your PC my second test subject for the Cam Plug-ectomy 🙂

  2. In replacing my cam plugs, I had the same problem as the gentlemen above in that two of the tappets in the front head fell out (if I only knew then what I know now). I haven’t found any extra shims but two of the tappets had two shims and one only had one. I looked hard for missing shims and fished around with my magnet but found nothing. Anyway, I put everything back together though I had to guess about where the single shim went. I started the bike for better or worse and the valves sound nice and quiet like before but the motor pops and misfires almost like I have a carb problem. My question is, could maladjusted tappets account for the misfiring or should I be looking elsewhere?

    1. Hi Chris,

      It’s possible that you lost a shim but there’s a good chance the shims you found and put back in are all there were. I believe that each tappet was checked at the factory and shimmed as needed so they might not all have the same number of shims. The procedure in the Honda service manual can be done to verify for sure although it’s kind of a pain to do. I chose not to because I was worried about losing another shim. Also I figured that since the tappets are hydraulically adjusting, the chance of it having a major effect was small. However, it is certainly possible that your valves are opening and closing a little late or early on one cylinder and is making the pops and misfires.

      What’s more likely is that you have a cracked carb insulator or vacuum line somewhere. Spray some carb cleaner around the insulators and see if the engine revs change. That’ll indicate trouble there. For the vacuum lines, try some soapy water.

      Check the carbs first before diving back into the head covers. Hopefully that’ll solve the problem with a minimum of pain.

      Cheers,

      Douglas

    2. Oh and I should note I’ve put at least 5k miles on my engine since I ended up with a “spare” tappet shim without any engine troubles. Not saying that it will be the case for your engine, but at least mine seems happy!

  3. Wow Doug, you are braver than I am. I just recently decided that I had had enough of putting a piece of cardboard under my bike whenever I stopped to catch the leaking oil. So I decided to replace my cam plugs. Like you I didn’t understand that the hydraulic lifters could remain in place or come up with the head. Fortunately I didn’t lose any pieces. But in reassembling my engine I noticed a tappet shim on the floor long after I had reassembled the carburators and had had actually taken her for a trial spin. This didn’t set well with me as I firmly believe that engineers put stuff in place for a reason. I elected to open the engine up again and find where the missing shim went which I did.

    One think to note is the torque values on the valve cover bolts. I managed to twist one too much and broke the thread off at the bottom of a 3-1/2″ blind hole. I had followed the service manuals torque values but found out that there are two pages with two values. Ordering new parts took about two weeks total. Yesterday I reassembled the valve cover with the proper torque values and was very much relieved to hear a nice running engine again.

    New problem. The engine idles at 4,000 rpm. I had to replace my choke cable as I broke it in the original disassembly. Am not looking for a choke cable adjustment. That’s how I found your site.

    Take care,

    A.J.

    1. High rpm issue solved. The carbs weren’t balanced.

      As you know you have to remove the carbs when you go after the cam plugs. And they have to be removed by separating them. This results in the balancing screw assembly coming apart too. Reassembling the carbs also means you have to play with the balancing screw.

      I adjusted the balancing screw, located between the carbs, by eye and ear. With the air filter assembly off you can look down the barrels of the carbs. If you give the engine some gas you will note that one side will respond while the other will not. Adjusting the balancing screw improves the responsivness of the lagging carb. A quick shake down ride proved that my eye-ear balancing was good enough for now.

      The best option for doing this is, of course, a balancing meter which I don’t have. My next endeavor will be rebuilding the carbs themselves. When I do that I’ll have that meter to fine tune my carbs.

      Take care,

      A.J.

      1. Hi AJ,

        Wait, what? You separated the carbs? Mine come on and off in one piece. No need to separate or rebalance. You can make your own carb balancing meter with some clear plastic tubing and some hydraulic fluid. It works like a charm and only costs a few $$. Next time, don’t separate the carbs. They come off as one unit 🙂

        Glad your bike is back to good health!

        Cheers,

        Douglas

        1. Hey Doug,

          Nope! I can’t remove my carbs without separating them. I wish it weren’t so.

          I also found the clear tube on a yard stick manometer on Leylands site. I assembled it and tried balancing my carbs. The only thing that happened was that one carb would pull the two strok oil up despite my twisting and turning the balancing screw. I couldn’t adjust the screw to a point where the oil just didn’t continue up. I didn’t want to ingest it into the engine so I stopped after about three tries. I then tried to balance it by ear.

          I found and bought a CarbMate electronic balancing meter. Should arrive in a day or two.

          New issue: I found yet another tappet shim on my floor. 🙁 It measures .0185″ That’s pretty significant. After reading about the tappet tolerance checks in the service manual I’m concerned that it needs to go back home. Are you still running without yours in place?

          Right now my unbalanced engine is running too warm to hot. It didn’t the first time around when I used the eye-ear balancing method. I’m hoping that I won’t have to take apart the front valve cover to replace that shim. And that a properly balanced engine will see running temps where they should be. If not then I’ll take the front cover off and find a home for that shim and try all this again.

          Take care,

          A.J.

          1. Hi A.J.,

            I’m still running without that extra tappet shim. I’ve put a lot of miles on the engine since then without problem. I *might* try to figure out where it belongs this winter when I have the bike torn apart to install the fuel injection conversion kit that I’ve been building but at least with the carb, it seems to be running correctly. Only time and miles will tell if I will have an early engine death or not. If only I didn’t have to take the WHOLE head cover off to figure out where it belongs, I would probably have put that tappet shim back in when I found it.

            Good luck finding the home for your wayward shims!

            Cheers!

            Douglas

  4. Douglas,

    If you’re still out there, I am planning to replace my cam plugs in a couple of months and have been reading every post like yours I can find on the subject. I am forewarned about the tappet shims; what I can’t figure out from accounts, the Honda parts ‘fiche or the exploded diagrams in the PC800 Shop Manual, is if the head covers have a gasket, or if you just use some sort of goo sealant. I’m sure I’ll find out when I open it up, but I’d like to have everything on hand that I need when I start. So, are there gaskets in there?

    Kel Williams, Springfield OR, 1994 PC800

    1. Hi Kel!

      I’m still out here but now much more busy than I was before. I haven’t been on the PC800 forum in months because I’ve been so consumed with my new job.

      The head covers use goop to seal them. I got some high temp HondaBond from my local Honda dealer that worked quite well. There are similar automotive compounds that you could probably find for a few bucks less at automotive stores. Just be careful that you don’t end up with a spare tappet like I did! Although… 10k+ miles later and I still haven’t had any ill effects from missing that tappet shim.

      Cheers!

      Douglas

      1. Greetings, Douglas,

        Wow, that was fast! I was expecting days. . . Roger re: the tappets; another post somewhere suggested cracking the cover up a couple or three cm and propping with blocks, then getting in there carefully and loosening the tappets from the cover to keep them in place on the head. I will try that, I think. I will have my son’s shop to work in, and a loaner to ride in the meantime since I ride year-round (my old BMW) from my other son, so no time pressure to do this right. Plus my brother’s a PC’er, and has had all his Tupperware off a couple of times. With him to help with the Tupperware party, and my son with the mechanicals (he is fearless about opening things up – has been building and rebuilding Jeeps for about 15 years now) I think we’ll get through it.

        I will find the appropriate goop. I am also planning to replace the hoses and spark plugs while I’m in there.

        Again, thanks for the speedy reply. Glad you’re still riding. My PC is my car, so I want to get this right and get it back on the road.

        Kel

        1. Hi Kel,

          Luckily I happened to be looking at my email when your message came through.

          The slowly opening the cover method is probably the best. Get some pencils or chopsticks to hold it open just enough to get in there with a (VERY WELL PADDED) tool like some pliers to make sure the tappets are staying down in the engine head holes. Those little tappets won’t like being marred by whatever you’re using to grip with.

          Another caution is to make sure you don’t drop ANYTHING into the engine heads because then you’ll have to pull the engine, open it up, and fish out the part from the bottom of the crank case. That’s a huge headache. I’m probably extremely lucky that didn’t happen to me in my naivety.

          One thing to note about replacing hoses is that there’s a hose on the gas tank side of the engine that I think you actually have to drop the engine out of the bike to access to replace. I bought hoses to replace everything and I still have that hose sitting in its package because I decided I didn’t want to pull the engine for that work. If you have a good shop to work in and a few strong young sons to use as assistants, pulling the engine isn’t too bad. If you are like me and working in a parking lot under a blue plastic tarp, it isn’t worth the effort.

          Your son is a Jeep man, hu? hmm… I just moved to Colorado and I want to get a Jeep or similar vehicle that I can take the top off of in the summer, and go explore with in the mountains here. I know very little about 4×4 vehicles but if he has any thoughts about things I should be reading to get myself familiar, I’d be all ears!

          Cheers!

          Douglas

          1. Hey Douglas,

            This is Jeremy, Kel’s son. I appreciate the info about this job and the responses to questions. We’re going to dive into this project tomorrow evening and plan to go slowly and carefully.

            Colorado sounds great! There are so many places to explore and I’d love to get my ’71 Jeepster Commando out to Telluride someday! As far as Jeeps go, I usually warn people off from anything but the newer models. That’s because the older models, usually meaning CJ’s, require maintenance and TLC. It would be prohibitively expensive to own an old CJ, unless you were mechanically inclined. If so, then the 76-86 CJ-7’s with the 258 six are a great choice. If you aren’t interested in more projects, then the ’91-96 Wranglers are great choices (square headlights). They added fuel injection in ’91 and updated a few other mechanicals. The 97-06 Wranglers (round headlights) are also great options.

            Please let me know if you have any other questions.

            Jeremy

            1. Hi Jeremy!

              Shoot me an email if you start having troubles and need someone to talk you through anything. I’ve got my bike apart right now so I can run down to the garage to look at it, etc. I don’t think you’ll run into too many problems though. Just go slow and watch for the tappet shims.

              Colorado is great so far! I’ve been driving a Subaru Forester XT since the end of October but it’s on a lowered WRX suspension so I haven’t been able to get off the pavement much other than little things like the shelf road and Phantom Canyon down by Cripple Creek. There are definitely plans to get a proper 4×4 to do some more interesting trails. My wrenching abilities are good but the space to wrench is basically nonexistent. We’re living in a townhouse with a two car garage. One half is taken up by Heather’s car and the other half is taken up by my workshop and the PC800 fuel injection project. I can do minor work out on the street or in the parking lot out back but I can’t do something like swap an axle or rebuild an engine on an old Jeep without getting into trouble.

              I’ve been looking at the 91-06 offerings in the YJ and TJ. Rigs out here in Colorado are pretty expensive for some unknown reason compared to what I’m used to in Oregon. I think probably I would go toward the TJ only because they’re marginally safer if I’m involved in an on-pavement accident (airbags, more chance of having the ABS option). Would probably want to find one that has the Dana 44 axles front and rear. Also I’m not sure if I want the short wheelbase version, the extended wheelbase two door version, or the extended wheelbase four door version. Each has their benefits and drawbacks. It seems a lot of people really like the 2006 Unlimited 2door version. Another question would be if I start with a bone stock Jeep and build it up (there are a few shops around that do custom Jeep work) or if I find something already kitted out and go from there. I’m not looking to have a massive rock crawler. I just want something I can go exploring with in the mountains and not be worried about getting stuck, breaking down, or dying in an accident on I-70.

              Cheers!

              Douglas

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