Topic: 1976 CB750F1

[fritzer_108]

I just picked up a junked CB750F1 cafe racer project and after my last experience with a 1973 CB750K3, I am very sure that the oil jets in the head are clogged. Does anyone know if there is a method for clearing clogged jets, or the does the engine need to be removed and the cam towers disassembled? The bike has been sitting dry in a garage for 5 years, but still has a great compression, clean carbs, and a decent wiring harness. My previous K3 had a Gordon style frame kit modification made, so tearing the engine apart in the frame was no big deal....not here.


Thanks!!!

[ekpent]

  If the top end cam and towers are fried there could be some telltale signs like metal in filter or maybe some piles up in view under inspection covers and if you have been there before real damage can happen quick. If it is truly and or the problem you know what you gotta do cowboy.

[seanbarney41]

Why are you sure the oil jets are clogged?  Out of the dozen or so 750's I have tried to put back on the road, only 2 had camshaft oiling problems.  I mean, it does not always pay to take the careful route with these.  Sometimes it's best to just cautiously send it.  I mean, really no other way to be sure besides pulling the engine and popping off the cam cover etc. 

[fritzer_108]

I haven't run the engine at all since I've gotten it. It hasn't been on the road in 5 years and was running great before then. I am considering the possibility that the oil jets are clogged because after I unclogged the jets in my K3, I noticed that I could see oil flowing from the cam towers if I peeped into a tappet cover while I kicked it over. This is not the case here. I spent 5 minutes kicking it over and it still looks very dry. I do know that the engine has never been opened and you can see see yellow loctite on some bolts.

[TwoTired]

Do you know what oil pressure you achieved by kicking it over?  Has the pump lost its prime from sitting?

Does it have the stock oil filter?  Is the pressure relief valve working properly?  Have you looked at the oil pick up screen to see if clogged?

I'd check all that before pulling the engine and taking it apart. Few can build a motor like Honda did at factory.  Though many have tried.

Cheers,

[fritzer_108]

I don't know the exact pressure as I don't have a gauge installed. I do know that oil is being pumped through the bike because oil seeped out of the oil galley plug above the timing cover on the right hand side when I loosened it. The oil filter is new and I checked the relief valve to see if that was working...it is. I will check the oil pick up screen.

[seanbarney41]

I would guess in five years most of the oil drained to the bottom of the engine.  I know guys with fresh rebuilds who have kicked and kicked and kicked and never saw oil pressure.  You may move a little oil kicking but you are not turning the oil pump fast enough to make running pressure.

I cannot guarantee that your oil jets are not plugged and the consequences of that are devastating, but 5 years sitting is really not very much in the grand scheme of these old bikes.  Unless you know of blatantly bad storage conditions, most have been successful with much worse.

[newday777]

Kicking to do that takes a lot of energy expenditure to get the light off and see the oil flow.
Why didn't you use the starter (with the kill switch off) to get the oil pressure light off and inspect the tappet caps for oil flow? I do that each spring before fire up after it's winter nap(this June it had been an extra long nap of 19 months, as I got stuck in San Diego last summer......  ) As long as the battery is topped off it will crank over and you'll know fast the oil flow to the cam towers is happening or not.

[ekpent]

If it was running great when put away and there were no signs of a top end problem back then I would not be paranoid of a clogged jet. I would do the proper prep and start it up to get some real pressure and then take a peek if you feel the need. A lot of 750's I have rescued have been laid up a lot longer then yours with no problems.

[Don R]

 If you can get access to an automotive AC oil feed tool you can use one to inject motor oil into the right side oil port and feed a pint to a quart at a time. I was able to turn off the oil pressure light for 30 seconds each time and get oil through the whole system.

[fritzer_108]

I started using the starter for short increments of time as to not burn it out and after a few minutes, I was able to see a stream of oil leave the cam towers by looking into the Cylinder 4 exhaust tappet cover. Thank you for the help

[newday777]

I started using the starter for short increments of time as to not burn it out and after a few minutes, I was able to see a stream of oil leave the cam towers by looking into the Cylinder 4 exhaust tappet cover. Thank you for the help

😉

[Don R]

 Awesome one less thing to worry about.

[Bankerdanny]

Oil doesn't turn to sludge just sitting the way that gas will. It just doesn't seem likely that the oil galleys would spontaneously clog from a few years of sitting. My F1 had been off the road for over 20 years when I bought it and honestly it never even occurred to me to worry about that. I changed the oil and filter, made sure the oil pressure light went off from using the starter, then I just started it. No oil issues over several thousand miles of riding since then.