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Another Vf500 Engine's Demise


YoshiHNS

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Sorry, I should have explained myself better. I didn't mean that we need another oil debate (God help us), but if it is going to be debated anyway, then it should be a separate thread rather than hijack this thread.

The original topic is of interest to me, not an oil debate.

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We are indeed away from the original subject. But there are several thing wich influenze wear and tear of an engine, one is oil. The only thing i say about oil is use a good brand and change it at regular times. (mileage or once a year)

I mentioned one other thing, without any reaction, but i think of interest. All damaged cilinders are burnt clean. So ik think, that a lean mixture may be one of the causes. Lean mixture means high temperature's, stressing parts like valves much more than under normal conditions.

Leaking insulators may cause a lean mixture, but leaking valves may cause that to. So controlling valve clearance and doing a compression test may be usefull. And when rebuilding i would ,measure the valve springs, they are 30 years old and may have weakened to much. A valve closing to late cannot dissipate its heat to the cilinder head. Or may even hit the piston.

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Absolutely VFRbert, I agree that nothing can replace regular maintenance, being aware of 30 year old weak valve springs, excessive heat from a lean condition like split manifold rubbers, over revving and the many other reasons for a valve failing.

Why are VF500's more prone to this condition than other bikes?

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The first thing i think about are the valve springs, they were relatively strong, because Honda switched with the vf series to a higher valve lift and used stronger springs, to close them in time. But stronger springs means more stress to the valve and valve stem. In time and in combination with other factors, like overrevving and overheating this could mean, the valve stem material is fatigued and the damm thing breaks. I had once a broken valvestem in a volkswagen diesel. Never seen such a mess. :wacko:

In addittion tho the stronger valve springs you have the dual cam follower, wich causes more stress to the parts also. Because of the fact, it has to open 2 valves, it has extra pressure from the two valve springs, causing extra wear and the risk of developing sloping wear, when pressure from both valves is different. All those things might give extra stress to parts.

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That makes perfect sense VFRbert, Honda occasionally do some strange things that cause issues, chocolate camshafts on VF750's, XR350's with insufficient oil capacity, screen door cam chain tensioners on VF's CB1000's, XL's with points on the end of a camshaft that was prone to float up and down with a bit of wear, etc.

Many years ago while riding my three year old1974 XL350 as fast as it would go along the highway, a rocker snapped and blew a hole in the cam cover, it was not uncommon and the fix was to use the 1976 XL350 rockers since they were much stronger.

Luckily it's not too often but this could be another example.

I have always thought that a VF500 would be a nice engine, but it seems that dropped valves are quite common.

Tony

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The VF series nearly costst Honda its reputation as a good engine builder. So they redesigned the whole stuff and astonished the world with the rc24, made the engine even better in the rc36 and put the camchain with its flimsy tensioner back in the 800 vtec. At the same moment accountants and controllers take over a company, they start to cut on costs and end up with inferior products, ending up with less sales. Quality will get worse for a period i think and then they are forced to make better products again, or shut down buissiness. At this very moment i think company's like Kawasaki which alway's made products, with some rough edges on it, produces some very good motorcycles. I hope Honda learns from its faults and start to make perfect products again.

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Yes, I remember that accountants almost sent KTM down the gurgler in the early nineties, poor quality, bikes that broke often and were not competitive.

Once the owners took charge again, they started making great quality motorcycles that won world championships and by some miracle, started selling motorcycles in big numbers, look where they are now.

Tony

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It is always a bummer to see a VF500F engine heading to the recycling bin. These are great engines (and bikes) but they do take some looking after (even when new & especially now after 25+ years with who knows what servicing).

Lots of good info above. If I could add, keep in mind the 500 owner's mantra: a proper warm-up (take the time to get the engine hot & not simply warm before riding), keep the revs in check (I agree this is very hard to do), use a high quality motor oil and diligently maintain the proper valve lash setting - use two feeler gauges here (while checking the lash take the time to also inspect the valve train - look for wear on the followers and cam lobes). This mantra will help to insure the longevity of these amazing engines.

For the valve springs - KPMI offered a VTR250 kit (now discontinued) which should be a match for the '84/'85 (the '86 being a different spec) VF500F. Last I checked with them (spoke with Warren Fong an engineer there a couple years back) they requested sending them a spare head so they could double check the specs. I didn't dive into this at the time as I have a low mileage 500 and a set of spare heads but if this engine is heading to the bin --- perhaps the good head is a candidate to send to them?

Having a source for new valve springs to match OEM would be a great find!

Good luck! Hope you are able to get your 500 back up and running.

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...

Having a source for new valve springs to match OEM would be a great find!

....

If I was to do a full rebuild on an engine, I would start with a VTR250 engine first, since it's half the parts. I would get all new valves, guides, springs, retainers, keepers from KPMI. Then I would start the foolishness and fit Ninja 250 sleeves in the VTR jugs. Then get standard size Ninja 250 pistons from Wiseco. If this all works, then maybe someone else more foolish than me would try it on their VF500 engine.

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^ Kickstarter campaign? ;-)

It's all about time. First priority is finishing the Magna VF. It already has someone willing to buy it, and I didn't succeed in selling it without an engine, so that has to go. Then start on a full rebuild of the Tomos as a early Bday gift for my sister. Then we now have TWO 4th gen project bikes (not my doing) that have to get fixed and sold ASAP (at least they both run). Have to finish the final bits on the F2 track bike before track days open up. Then I can start on the fun stuff.

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...

Having a source for new valve springs to match OEM would be a great find!

....

Did a bit more research on the above. Ed Stewart from CV Products (Xceldyne) confirmed that they unfortunately do not offer valve kits (valve springs) for the VF500F. I think this is a snafu on the JCW site.

I think the best bets are either KPMI (bringing back their discontinued VTR kit) or R/D valves. I confirmed with both (now a couple years back) that they would require a spare head in good condition to check the specs - but both felt they could offer kits for the mighty 500.

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IC. I came across a thread on VFRW where you said you attached an arcticle showing how Honda said that the VF500 engines were made to maximum capacity (could not be bored out any larger). Do you still have that article? That would make sense if the VF500 was based on the 400cc V4 engine.

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For the valve springs - KPMI offered a VTR250 kit (now discontinued) which should be a match for the '84/'85 (the '86 being a different spec) VF500F. Last I checked with them (spoke with Warren Fong an engineer there a couple years back) they requested sending them a spare head so they could double check the specs. I didn't dive into this at the time as I have a low mileage 500 and a set of spare heads but if this engine is heading to the bin --- perhaps the good head is a candidate to send to them?

I could send them my 86 head with one side smashed and the other okay. But is there enough demand for them to bother? $400 to update a (nearly) 30 year old engine? New springs would be great for a preventative measure, but if you have a broken valve, you might have a seat damaged beyond repair, and then more costs pile up.

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^ Sending a spare head is definitely a postive thing but I have a hunch this will be up to the individual owner - more a restoration/challenge thing than a group effort. On a side note, the '86 engine has its own unique design so I think there would be more of a market for the '84/'85 which have the same valve spring part numbers and are a match to the later VTR250. The '86 is of course a great engine (some say an improvement over the '84/'85) but there are simply not very many '86s out there as they had a limited production run to start with.

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So with what little time I've had, I've managed to take out some of the valves and all the springs from the smashed 86 head. All the springs are well within spec. The two good intake valves I managed to take out were on the low limit for the valve stem OD. The two good exhaust valves that won't come out feel pretty sloppy in the guides. So unless someone can come up with a spec on the spring rate, I can't see the springs being the culprit. I can compress the springs (not fully) somewhat easily with just my hands though.

PS: I've uploaded the 84-85 VF500C service manual to the site. The engine should be the same as the F version.

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