VF750F Oil Mod - Beating a Dead Horse.

So, I've owned my '84 Interceptor for 8 years and 10,000 miles now, and the intermittent rattling from the cam chains is getting worse. I'm just about to tear into the top end to replace the camshaft tensioners with the later style units I snagged off of eBay for a grand total of $7.50 plus $14.00 shipping. I've been thinking about the various oil mods that have been attempted over the years all with the goal of increasing oil pressure/flow to the top end. It strikes me that compared to adding external hoses and tapping a different location for the oil feed to the camshafts, the most elegant solution would be to machine new oil pump drive sprockets to increase the oil pump rpm relative to the crankshaft. This should increase the flow of oil produced by the oil pump and subsequently the oil pressure at all rpm's, especially at the lower end of the rev range. Has anyone else ever attempted this mod or heard of someone who has?

 

if u need big mods to keep a bike runnin, maybe its the wrong old bike. people may love their vfs but theyre antiques compared to the vfrs that came out just 2 or 3 years later.

 

Eh, from what I gathered on various forums and through testing, the gen 1 oil pump just simply does not flow a sufficient amount of oil to keep the main bearings and the camshafts at an adequate oil pressure. Hell, at 1,200 rpm idle the mains are getting 12 psi and the camshafts are receiving a bit fat 0 psi of oil pressure. When bumped up to 6,000 rpm, the maximum oil pressure was attained at ~80 psi mains and ~20 psi at the camshaft. Over 6,000 rpm the pressure relief valve kicks in and all the extra flow capacity of the pump is wasted. Most of the engines with significant camshaft wear were bikes that were ridden at low engine rpms, and the worst offenders also had bearing clearance problems which simply exacerbated the low oil pressure problem. Pretty much all of the usual oil mods traded a bit of main bearing oil pressure for more camshaft oil pressure. And when examining the camshaft bearings, they do not fully surround the bearing journals. This means that any quantity of oil that makes it to the camshaft journals simply get scraped off on the opposite way round. The oil is not able to be recycled internally in the bearing journal as is the conventional for many other successful engine designs. Ultimately this results in a bearing design the requires more oil flow than a conventional plain bearing that fully surrounds the bearing journal. The permanent fix would be to increase the flow rate of the oil pump and increase the diameter of the orifice in the banjo fitting supplying oil the camshafts. I noticed there is sufficient room in the crankcase to permit changing the oil pump sprockets size which would lead to an increase in oil pump flow rate.

 

Go here for the Good Oil!

https://www.motorcycleproject.com/index.html

https://www.motorcycleproject.com/text/v4_cams_what.html

 

Thanks for the link Terry. I knew I read those articles before, but I couldn’t find them again.

 

Mike Nixons explanation seems plausible to me. I know nothing about VFs but I have seen a few pitted cams and followers in my pre VFR days.