1st Gen VF500F Re-Bore: Anywhere to find oversize pistons?

Hello all,

I am relatively new to the forum and have posted twice elsewhere regarding my '86 VF500F, after picking her up in January. It is truly a beautiful bike, however the engine is in a less than spectacular condition.

I've been working avidly on this thing for almost 2 months now. One thing led to another, and now the heads are off, revealing the piss poor maintenance this thing endured. I'll list below the compression on all 4 cylinders I measured as well as clearances on intake and exhaust valves, as well as factory specs according the Clymer manual. All measurements were performed while the bike was cold, and drained of oil.

Factory Specs:
Compression should be at 142-199psi
Valve clearance should be .15mm(.006in) for intake and exhaust

Cylinder 1: 115psi, .18mm intake, .15 exhaust
Cylinder 2: 70psi, .28mm intake, .18mm and .00mm on exhaust valves
Cylinder 3: 100psi, .18mm intake, .15mm exhaust
Cylinder 4: 80psi, .18mm intake, .15mm and .00mm on exhaust valves

My question to the forums would be whether anyone at all knows where to get oversize pistons for this bike, if they even exist at all? And if they do not, whether I would be able to get away with a professional hone and some new(er) pistons, as well as some new(er) heads on both cylinder banks with new(er) valves all around? I will attach pictures of the cylinders as well as valves. A straight up nick in one cylinder 2 intake valve, seems like a crack in a cylinder 3 intake valve as well. Particularly concerned with cylinder 2, the one with a little corrosion on the bottom wall.

TL;DR anywhere to get oversize pistons/rings or a big bore kit for an '86 VF500F or V30 Magna?

 

You won't be riding soon unless you find a bike that runs. too many 500 parts are NLA.

 

Can't offer too much help. Just thought I'd wish you luck in your search. Perhaps you should try picking up a 2nd-hand engine (known good), as alluded to by the squirrelman. Otherwise, I suspect it might get long-wnded, pricey, or both.

Must admit, I liked the VF500 bikes back in the day...definite step up over the Vf400 bikes...

Again, good luck with it. Hope you get it back on the road.

 

Thanks guys. I appreciate any help I can get. This thing has turned into a nightmare... but it can be done. I've found a few engines for this thing online, and I'm heavily considering just slapping a known good one in there. Cringing at the bite it will take out of my wallet, though.

"We can rebuild him... stronger... faster"

 

The pictures are not very clear, but the cylinder bore looks okay to me. I would get it honed, clean both mating surfaces, and just replace piston rings. Your low compression numbers could be just worn rings. If I remember you can test them by checking the gap with feeler gauge.

Either way, good luck.


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And also notice aren't the low compression cylinders the ones with no valve clearance.

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This was my initial plan, to get a professional honing done, and sort of freshen up the cylinder heads and pistons. One problem though: I've been searching for several days now and have so far come up dry for pistons rings. Does anyone happen to have any resources to track any down? I'm going to look over a parts diagram for the cylinder in a few minutes and see if I can do a reverse lookup.

May be a dumb question, but would the lack of clearance be a factor in the low compression on cylinders 2 and 4?

I will see if I can get some better photos of all cylinders when I get home today.

 

I'm no expert but I believe lack of clearance can certainly cause low compression.

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Well, I found that a replacement set of piston rings are very expensive. At the rate it would cost me to rebuild the engine I have, I could likely buy another one and swap them.

Perhaps I will swap the engine and begin collecting spare parts for the future on the side.

Will post updates

 

I can't see a crack in a bore, which pic?

Why is the head on the rt in the pic covered in brown gunge?

Aside from this, yes the zero valve clearance will give reduced compression

Am I correct in assuming you haven't had the Pistons out?

If so you can just clean all that lot up, lap the valves in, new springs and rebuild it

Check for water in the engine oil, run flushing oil thru twice, if all OK you've got a runner

Good luck

 

Heads got water and stop-leak all over them when I pull them off the engine. Someone had loaded up the coolant supply with stop-leak. I think you're talking about the head off of cylinder 1 and 3. Those heads were actually okay.

There were no cracks in any of the bores, but one intake valve did have a nick, in cylinder 2 I believe. I haven't had any of the pistons out. I'll see if I can some better pictures and post the clearance I get from the cylinder wall and piston ring in all cylinders this evening.

Thank you all, you've all been very encouraging and helpful. I really hope the simplest solution will work to get this thing back on the road.

 

Did you try Honda dealership? The rings for car are usually not more than $50, so knowing it’s bike and everything is 4 times more shouldn’t be more than $200 for them?


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NLA baby, N-L-A !!!

Problem with finding a good-running vf500 engine is, none left except those in a few bikes. no shame in giving up and finding a better bike to ride. fix the low compression on that bike and you may have the classic valve dropping syndrome soon after ?

Anyone with good sense would have done a compression test b4 buying, as few replacement parts are available, and 500 engines--as reported on this forum--are highly prone to self-destruction. Honda's rare mistake.

i believe the pistons and rings from the Honda 1988-1990 VTR 250 may be same as 500, and at least one company did make higher-compression pistons for the VTR. if you can find any.........

 

Thanks a bunch squirrelman. You may have just saved me with this information. This whole project has been a huge lesson learned in old machinery. I've worked on classic cars my whole life growing up in a family of mechanics, but never have I undertaken a bike on my own.

I'll continue to cross-reference different bike models and their respective bore/strokes/compression ratios to see if I can Frankenstein this thing together. At least enough to enjoy it for a while.

 

VF500 engine problem posts here usta be weekly and monthly, mostly valve-related. they've broken alot of too-innocent guys' hearts and bank accounts. OK, the VF500 is a cute little package, but she has VD (valve disease).

one of the smoothest engines ever when it was new, but most have valve spring problems sooner or later or poor maintenance failures.

 

Yes sir, and the valve pitting a problem also, and no parts available to fix. I put my third (and last) engine in last year. Wonderful motorcycle and running fantastic again, but it leaks oil. And has a pitted valve stem. Can't really ride it. Oh, I take it out occasionally, but it's a toss of the dice.
It really is a beautiful machine though, buttery smooth all around, fat midrange, nimble. And I often admire the looks, how the engine was exposed on these models, decently finished with even some chrome bits.

It's just really tough to keep em going at this point though.
Best wishes, hope you get it all worked out.

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If the bores aren't damaged then no need for new rings

Walk into any decent motor factors and they'll find a match for the valve and springs

 

[QUOTE="Thumbs, post: 581583, member: 31380Walk into any decent motor factors and they'll find a match for the valve and springs[/QUOTE]

you really believe that ??

 

Any parts available for the valvetrain on this bike are going to be used unfortunately...