VF500F compression test help

Discussion in '1st & 2nd Generation 1983-1989' started by mikemo, Sep 25, 2020.

  1. mikemo

    mikemo New Member

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    Hello all. New guy here with an old Honda.
    I just bought a 1986 VF500F in desperate need of attention. Here's my intro post:
    https://vfrworld.com/threads/oh-my-what-have-i-done.58734/

    The bike ran when I looked at it, and seemed to run on all 4 cylinders. It has 23k miles on the odometer, but the speedo cable is broken. Whatever numb-nuts mounted the front wheel didn't set the speedometer gear assembly in the right direction. Instead of fixing it, they bent the speedo cable in an almost 90 degree bend to mount it. Obviously, it broke internally. By the age and wear on the (incorrectly sized) tires, I would guess that there was another 4-5k miles on the bike itself.

    I got the bike home last night and wanted to do a compression test on the engine before I started ordering tires and a chain. I just finished that up and here are the results. I was hoping for the opinion of the experienced members here about what I see.

    This was done cold and dry.
    1 135 psi
    2 155 psi
    3 120 psi
    4 130 psi

    I was concerned with #3, so to test further I put about a tsp of Marvel Mystery Oil into the cylinder, rotated the motor a few times, then rechecked. The reading jumped quickly to 170 psi.

    I'm really hoping that this bike can be a good runner without having to do any major engine work. I do want to check the valve clearances, but need to find new gaskets first. Any pointers?

    Thanks in advance for any help.

    Here she is, waiting for the compression test. Probably the first time this bike has seen a garage in a very long time :)

    20200925_152146.jpg
     
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  2. squirrelman

    squirrelman Member

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    smart to check compression b4 going further. numbers show u gotta runner although not perfect. most vf500 buyers open themselves to alot of serious running problems, hopefully not u.

    next u need to inspect top of vales stems for signs of "mushrooming" and make sure clearances are correct. new gaskets are not needed to open valve covers.
     
  3. raYzerman

    raYzerman Member

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    For cold, I don't see a lot wrong with those numbers.... any cylinder is bound to rise with oil...... what you should do is check it again with things warmed up so all the metal bits are expanded, i.e., oil circulated, rings seated into cylinder bores, pistons expanded, etc. I would expect the numbers to even out somewhat when warmed up, but again, not too bad at all right now.
     
  4. BoomerDave

    BoomerDave New Member

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    Choke off, throttle wide open, warmed engine, then take readings. Take them again to make sure you had the hose screwed in all the way into the hole. You are looking for differences between the cylinders more than just the amount of compression. The "squirt of oil" test is okay but not definitive, just one more layer of info. A leakdown test is the next level up in testing, to determine whether it is the rings or the valves.
     
  5. squirrelman

    squirrelman Member

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    if it's the valves leaking u can often hear leakage by using a wrench to turn the crank and listening at the carbs or exhaust pipe.
     
    Last edited: Sep 27, 2020
  6. mikemo

    mikemo New Member

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    As suggested, I took off the valve covers to have a look at the valve tips. Things were looking good until I got to #2 exhaust side. Here's what I saw: DSCF1606.JPG

    The tip of the valve looks pitted and worn. I could see this without loosening the adjuster, but I backed it out to take the picture. Both exhaust valve tops on #2 look like this. I looked at #4 exhaust valves and one was similar to this, the other just had a tiny bit of pitting right at the center of the valve tip. There was clearance between the rocker and valve before I loosened the adjuster. Because there is some sort of gasket sealer on the valve cover gaskets, I have to assume that these have been adjusted at least once in its life.

    I'm guessing that this is bad news, and my heart kind of sunk when I saw it. Is this how "dropped valves" begin?

    Any advice will be greatly appreciated. Thanks
     
    Last edited: Sep 27, 2020
  7. squirrelman

    squirrelman Member

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    :(

    only 23k miles, it should be OK to run it till it blows. what's your other choice ??
     
  8. mikemo

    mikemo New Member

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    Thanks Squirrelman. No other choice, I suppose. When you said to check to see if the valves were "mushroomed", I guess I didn't know exactly what that would look like.
    I don't have a 3mm square tool to adjust the tappets, so I ordered one. I'll get the valves adjusted as best I can, try to get the petcock to stop leaking, adjust the chain and take it for a ride.

    Thanks again!
     
  9. squirrelman

    squirrelman Member

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    it will last longer if u keep the revs down and don't go to the redline. any pitting on cams, and where's the locknut ?
     
    Last edited: Sep 27, 2020
  10. BoomerDave

    BoomerDave New Member

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    Not sure why you are focusing on the top surface of the valve stem before you figure out what is going on inside the cylinders. Have you done a leakdown test yet ? Have you checked valve clearances yet ?
     
  11. TimKVF500F

    TimKVF500F New Member

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    These engines tend to have valve problems that first become apparent with wear on the valve stem tip.

    I would still like to see exactly what the "mushrooming" problem looks like, Mikemo it looks like a chip is missing on yours? Any other pics would be appreciated, I am in nearly the same boat. I have a 1985 with 17K that I got up and running after a 17y slumber, put a few miles on but haven't checked the valves yet. Thanks!
     
  12. mikemo

    mikemo New Member

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    Boomer,
    I was just reporting what I found after inspecting the valve-train. What I'm really trying to determine is if this bike is worth saving, or if it should be parted-out. If the motor was trash (or on its way to be trash) I wasn't going to continue to bring it back to riding condition. The bike wasn't very expensive, but I don't want to throw money down a hole. I borrowed a leak-down tester from a friend so I can get some more data. How do you keep the crankshaft from spinning when you do the test?

    TimK,
    Yes, it does look like a chip, but it's hard to tell. I've never seen a valve tip that looked like that, but I'm not a mechanic so my experience is limited. The cam lobes look fine so I don't think there was a lubrication issue. Maybe the bike was just poorly maintained. You should see some of the unbelievable things I've found so far that have been caused by previous "mechanics". Have a look at the gaskets on the clutch line. I couldn't help but laugh.

    20200927_111909.jpg
     
  13. BoomerDave

    BoomerDave New Member

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    I have not done the test on this particular bike yet, but you need to hand crank to TDC on the compression stroke for the cylinder you are testing. If you don't have the shop manual check for Youtube videos on how to do a leakdown test, it is not difficult.
     
  14. TimKVF500F

    TimKVF500F New Member

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    Honestly, I would probably adjust the valves, rebuild the carbs, and have fun with it. You mentioned it was running prior to purchase, did it smoke at all? When or if it ever blows up, you can part it out or hunt down parts to rebuild, whatever path is most appealing you... lol
     
  15. mikemo

    mikemo New Member

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    Tim,
    Yeah, that's probably what I'll do. The bike had some white smoke leaving the tailpipes, but it looked like water vapor. When I drained the tank there was about a liter of nasty brown water in with the very stinky gas. I think the only reason it was running was that the petcock was stuck on "on" so it wasn't drawing the water directly from the bottom of the tank. So no surprise that there was some steam in the exhaust. I'll know for sure if it is a smoker after I get the valves adjusted and the covers back on.

    Thankfully the tank is really clean inside. The outside is terribly faded and it does have a dent. I would guess it came off a parts bike that lived in the southwest US, dry and sunny. I also disassembled the petcock and cleaned it out. Hopefully it will stop leaking when I reinstall it.

    If I can get it running worthy of a paint job, I'm thinking of painting it with Porsche "Miami Blue". Kind of like a 1990 Honda CB-1 blue.

    Thanks
     
  16. straycat

    straycat Member

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    mikemo, you may not need a 3mm wrench to adjust the tappets. you can likely make one easily from a Robertson head screw. I took a 3" Robertson screw and bent it 90 degrees at the head and made my tappet wrench that way. once you loosen the lock nuts the bent screw Will adjust the tappets no problem.
     
  17. BoomerDave

    BoomerDave New Member

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    Good for you to try to save it, I just went on my last ride for the year on mine and will surely miss it until spring.
    It was worth all the effort to get mine running right.
     
  18. TimKVF500F

    TimKVF500F New Member

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    That is great to hear about the tank. Even though mine was stored inside, it sat for 17 years in humid Maryland, a lot of pin holes along the bottom edge.

    Keep us posted on the progress!!
     
  19. raYzerman

    raYzerman Member

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    Had to chuckle.... just where would an American find a Robertson screw, lol....
     
  20. mikemo

    mikemo New Member

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    Well, now I know what a mushroomed valve stem looks like. I started adjusting valves today and I got to #4 exhaust. The inner valve looked fine. The outer valve, however, did not. If you look at the full-size image, this valve stem is obviously damaged. I was going to adjust valves and take the bike for a spin, but looking at this, it seems to me that this is a ticking timebomb. Since the bottom end is in good shape, I don't see the sense in damaging it by running this any further. It's easy to see how this could crack, drop the keepers and then drop the valve into the cylinder.

    What are the chances of finding replacement valves and a head gasket? Looks like exhaust valves are available (maybe?) from CSMNL at 45 Euros each. Times 8 valves, is about what I paid for the entire bike. Maybe it is time to call it a bad purchase and just part out what I have to try and recoup some of the purchase price. I'm disappointed :(

    DSCN0819.JPG
     
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