VF500F compression test help

sorry, and i hate to say it, but if you came to our forum b4 buying you'd have been advised not to gamble on buying that bike, and it's not worth rebuilding imo, so just move on. the problem that leads to valve damage can be blamed on weak springs that allow valve float at higher rpms, and honda issued a bulletin calling for replacement of springs by 20,000 miles i believe.

you're another in a long line of hopeful riders whose dreams were ruined by the flawed VF500. and since so many are dead and in boxes under workbenches, parts aren't worth much unless they somehow look new.

 

Why replace all valves? Are they all bad? Just replace one or two that's needed. To remove mushroomed end, grind around outsides with Dremel stone to remove flare so it slides through guide.

Factory OEM valves aren't only ones that fit. Possible to get aftermarket or custom valves from various vendors in higher-performance formulations at lower prices: Ferrea, Del West, Manely, Edelbrock, SI, etc. I recently rebuilt Porsche head with SI valves (stainless intake, inconel exhaust) for less than cost of OEM valves. Also installed copper-beryllium seats, fully-radiused.

I ended rebuilding my VF500 about 10-years after buying it new. Damn teenage 1st owner hadn't learned how to maintain bike...




Last 25-years has been much, much easier!

 

Ouch. Cut the line and let it go. Look for donor bike or look for something different.

 

I love the different viewpoints of the last two posts!! lol

Dannoxyz, how do you go about getting custom valves? A set of measurements/diagram or sending them an example to copy?

 

I raced a VF500F and currently own about 15 V-FOURS. It will snowball out of control and you will think that you have to finish it.

Can of Worms.

I love my 500s. But it's gotta be that High School bike or a dead relative's. They will make you pay.

 

Yes, either will work. Faster if you do all measurements first and send them drawings. Also easier to submit for multiple bids that way.

Be aware that I’m not afraid tinker. I’ve designed and built my own trellis frame. Casted my own engine block for CRX race-car.

You may not want to go through such extreme efforts when easier paths are available. Fastest and cheapest to get replacement ‘86 engine from breakers. Note that earlier ‘84-85’engines won’t interchange many parts. You can swap in entire engine though, slightly easier due to narrower valve-covers. Inspect engine carefully before buying.

Then it also depends upon condition of frame & suspension. Make sure there’s no hidden surprises lurking there.

 

OK, that doesn't look good and this was an issue back in the day. There is a service bulletin that covered this and Honda supplied dealers with end caps to fit on the valve tips. I suspect this idea was short lived as fitting them would be a PITA. It it were me I would just set the clearances as best as possible, button it up and ride it and as suggested, keep the revs down. I would then keep a close eye on it and maybe after 500 miles have another look and compare photos. If it is stable then keep going. A tear down to fix it is not worth it. It will be shockingly expensive IMO. If the bike is a keeper then buy a spare engine which is exactly the same year and see if you can use the parts from that to fix it. It all depends no how much you are going to use it.

 

What? no Robertson's in the USA ? Surely you jest ?

Has to be one of the greatest inventions, comes second only to the "Wheel"

 

Ok guys, I put it all back together this morning. It seems that only the front two cylinders have damaged valves. The others had a wear spot in the center of the valve stem, but didn't look damaged. One valve on #2 has a chip and one on #4 is a "mushroom". I set the clearances as close as I could, but that valve with the mushroom tip was just about impossible to set. I'm sure it is too loose now. The bike started right up and ran fine. I adjusted and oiled the chain, filled up the rock-hard tires, then took it around the block. It wasn't perfect, but it seemed to run strong. There's quite a distinct tap coming from the #4 exhaust side (no surprise).

So could I get something like this: https://ebay.us/Fezoph and (assuming that it is good) replace the front cylinder head? Can you still get quality head gaskets? Caveats?

What are the chances of finding a good used motor for this bike? Seems slim to none.

I took my cheap infrared thermometer outside and measured the temp of the exhaust pipes. Strangely, #4 seemed about 40C hotter than the rest of them. Maybe too lean? Maybe that caused the issues on the exhaust valve?

Thanks again for the help!

 

Could also be clogged carb on #4.

Here's VF500F engine near me for sale:
https://sfbay.craigslist.org/nby/mpo/d/angwin-selling-japanese-engines-for/7203302964.html

I usually bring battery and do compression-test on spot. Take off valve-covers and look at valve-tips.


Valve-tip caps has been used for decades, very common on older engines with softer valves:
https://vwparts.aircooled.net/Manley-Wear-Cap-7mm-2740-Set-of-8-p/42100-8.htm
http://trendperform.com/n-11644-tit...find-supremacy-in-the-racing-valve-train.html

You can actually replace valve-springs, valve-stem seals and do tip-repairs without removing head from engine.

Anyone used Athena headgaskets? Call Cometic for headgasket, they have pattern stored. I get Porsche 951 headgaskets as one-offs from them in +2, +4, +6mm over and they make it when ordered.

 

I got the front head off today to take a better look. Here's an unobstructed view of the valve stem (#4 exhaust). Looks like it got the crap pounded out of it.




It's more concerning looking at the bottom. The valve with the damaged valve tip is sunk significantly into the head.




It is the lower-right valve in that picture. That tells me that the valve seat is likely damaged. It's interesting that the damaged valve looks like is was running hotter than the other exhaust valve in that cylinder.

So, did the valve sink, which reduced the clearance, then the valve tip got damaged? What would cause the valve to sink like that?

I bought an '86 front head off ebay that was fairly cheap. It also has some valve tip damage, but no sunken valves. Also, whatever meathead disassembled the bike at the junk yard mixed up the cam caps. Maybe the machine shop can make one good head out of the two of them.

Since I'm in this deep I'm going to pull the rear head too and bring them all to be evaluated. If the repair work is too expensive (or impossible), I guess I'll pull the bottom end of the engine out of the frame and start looking for a replacement. Or, as was suggested before, I'll just "cut the line" and let her go.

 

chances of finding a good replacement engine are exceedingly poor given the known problems and high demand for replacements.

 

I dropped off the front head from this bike, along with an Ebay head that I bought on a whim, at a local machine shop. They evaluated both and the verdict was that neither was in good enough shape to easily permit a good repair. The guides were shot, all of the exhaust valves were out-of-spec, and some of the seats would need to be replaced. All of these things could be fixed, but considering the cost of parts, it needed more money than is practical to spend on this bike.

I'm sad to say that I'm throwing in the towel on this bike. I'm going to pick up the heads from the machine shop tomorrow, then rolling her out of the garage.

I know I could bolt it back together and make it run again, but I couldn't sell it with a clear conscience knowing the state of the top-end.

I will be parting it out to try and recoup some of my losses. There are a few things that should hold at least a little value. A rust-free tank, good aftermarket igniters (from v4spark.com), frame with clear title, OEM gasket sets (top and bottom end), etc. I'll post it up on the classifieds list tomorrow.

Thanks all for the advice along the way. I learned a bunch.
Mike M.

 

With old bikes it's win some lose some, don't get discouraged.
Good luck on the next one.

 

fair warning, kids !! this story is common, so don't buy any cheap VF500 unless you hear it run and do a compression test first.

 

I'd add to that "don't buy a VF500 unless you hear it run, check compression, and remove both valve covers and inspect the valve stems for damage".

This bike ran and had reasonable compression on all 4 cylinders.

 

Yeah tell me about it. I am one the yahoos who went "all in" on a cheap VF500F.

I took a chance and now have a ton of "character building" to talk about LOL

.........DM me if you are parting it out.

I could use the fuel tank and petcock if it;s not too bad.

 

DM me if you are parting it out also.

Sorry to hear she's done

Sent from my SM-N950U using Tapatalk

 

Part out thread is posted in the classifieds section. Hopefully some parts of this bike will live on.