Topic: Engine/Oil Temperatures

[Crimson750]

Hey guys,

I recently got my 78 750 FK running. (F frame, K engine) I tore down and put back together the K engine I had. When putting it together I tried clearing the oil feeder passages the best I could because I know the little oil jets that sit beneith the cam holders have very fine holes. How would I tell they got clogged? But back to the title of this post. Assuming the engine is not oil starved. How would I tell the engine is overheating? What is the temperature range of a K8 when its running at 35 mph at 3k rpm and 65 mph at 5k rpm? I have a turkey thermometer stuck in between the engine fins taking temp. Those readings give me around 240 to 250 degrees F at 65 mph at 5k rpm. I couldn't get the oil temperature. When I took the oil temperature when the fins were reading around 240 to 245 after I got back from a short ride the oil temp was around 175 F. What is overheating, what is normal?

Bike info. stock 750 F carbs with 115 jets, mac 4 - 1 exhaust....carbs out of tune...boggy at hard wot. Engine is a K8

Thanks,
R.

[flatblack]

None of that sounds bad to me, based on what I know about air-cooled engines in airplanes...

Two things:

1. You don't want to see cylinder temps above 380 or so dF. Above that, aluminum alloys can start to lose their properties (the technical term is "funky"  ).

2.  You want the oil to get hot -- to evaporate any water -- but not too hot. 175 or so is good, IMHO. 160 or below after the engine is thoroughly warmed up would be too low. Anything above 200 and I'd start thinking about ways to cool it down.

I guess one could get really anal about temps and mount oil and cylinder gauges, but it seems like a lot of overkill to me. If the rebuild went well, your jetting is right, you use a good-quality oil, the bike's cooling fins are clear and you keep moving (i.e., not a lot of stop and go traffic), I wouldn't give it another thought.

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[scondon]

Hey guys,

I recently got my 78 750 FK running. (F frame, K engine) I tore down and put back together the K engine I had. When putting it together I tried clearing the oil feeder passages the best I could because I know the little oil jets that sit beneith the cam holders have very fine holes. How would I tell they got clogged?

    You can tell if they're clogged by the horrible screeching sound of your cam eating the towers. Seriously though, if your worried then take the valve adjustment caps off and run the engine(after it has warmed up). You should see oil spitting about. I had a clog in one of my towers and it was obviously not getting oil when viewed through the adjustment port.

   Can't tell you the temp that oil is supposed to run at, but usually the exhaust headers will "tick" a LOT when you shut off a bike that is running very hot. Usually a symptom of a "lean" fuel/air mixture.

   is your F a 75-76 model?

   

[TwoTired]

 Engine oil needs a certain temperature range to flow in the engine as the designers intend for the clearances they've chosen.  The "normal" operating range of petro oils is between 180 and 230 Degrees F.  Oil can begin to break down and lose its beneficial properties if it is heated beyond a certain point and that varies with the formulation and quality.  Usually 250-260 is an upper limit.  Some synthetics don't break down till even higher.  But, some begin the evaporate rapidly above 240.  There are lots of different oils.

Just as important is where you measure it's heat content.  It gains a great deal of heat while being squished in bearing journals.  Probing these points is problematic.  It's usually either the oil on delivery or the oil just after use that is measured.  I don't know how much oil remains in the bottom of the 750, as it is a dry sump system.  But, that is where the oil should be the hottest and have measurable access. The main oil gallery is where you'd measure to find out the delivery temps before engine heating.

Oil Temp guage manufacturers know a thing or two about oil temps.  Many of them center the needles on 210 Degrees.

Cheers,

[Crimson750]

This particular engine is a 78 K8. I'm not sure if my mixture is right. The jury is still out on that one. I'm in the process of riding it and reading the plugs which I haven't done yet. After today though, I should get a good indication if its too rich. Before I was running 105s on my F3 engine and that was running way lean, even though stock the jets were 90s. Stock jets on the K8 were 110s so I'm not that far off stock for the K8 but I'm not sure if the jets are right or not. The exhaust system on this engine and for the F3 is a Mac 4 - 1.

Ok, When I take the bike out next I'll bring the thermometer and I'll measure the temperature off the oilpan. It is right above my exhaust system so I'm sure its picking up heat from that. As for the oil I'm using its Spectro Golden 4 Synthetic 10w-40. Where would I find Oil temp/pressure gauges for my 750? And would I be able exchange them between my F3 engine and my K8 engine? From what I've found it seems as if I'm ok, I just don't want to have to rebuild this engine because of any oil problem because its my spare. I'm in the process of restoring the orginal F engine that came with the bike. Would an oil cooler be too much? I live in the North Eastern part of the US. Say the New England area. Yeah, it doesn't get as hot here as it does out west but we do have our 85 to 90 degree days.

[Clyde]

Rather than get concerned about the temperature I would be more concerned to be sure that the oil is getting where it is designed to go. Especially after a rebuild.
As Crimson750 stated I always take the exhaust valve covers off (one at a time) and start the engine to make sure that the oil is getting to each valve train. There should be a spray as you rev the engine up to say 3-4000. Keep a rag handy.
I have run a 810 engine in pretty hot conditions in Australia with no problems. If your engine is stock then I see no problems with overheating
Regds Clyde

[Clyde]

Sorry
I should have said "as Scondon stated"
Regs Clyde

[Gabus]

You could buy a temp gauge that replaces the oil tank cap for 35 bucks

[scondon]

This particular engine is a 78 K8. I'm not sure if my mixture is right. The jury is still out on that one. I'm in the process of riding it and reading the plugs which I haven't done yet. After today though, I should get a good indication if its too rich. Before I was running 105s on my F3 engine and that was running way lean, even though stock the jets were 90s. Stock jets on the K8 were 110s so I'm not that far off stock for the K8 but I'm not sure if the jets are right or not. The exhaust system on this engine and for the F3 is a Mac 4 - 1.

   Are you using the same carbs/rubbers for the K8 that you used on the F3 engine? F3 intake ports are 2mm larger than K8 and require a larger carb rubber. If you swap in a K8 engine without changing rubbers then you will have a loose fit, prone to air leaks.

  F3's are jetted 105 main stock. They run a bit lean but not by much. I put a K8 engine in my F3 and ran for a year and a half with the 105 mains and did not notice any problems running lean(stock airbox,exhaust).

    If you're using F2-3 carbs/rubbers with stock airbox/filter then you may want to check for leaks and jet down to 110.

    What type of carbs are you using currently? Stock air filter? Hows your ignition timing? Stock points/condensors?

[Crimson750]

I am running the same carbs. on my K8 as I do on my F3. The rubbers between the two engines are different. The carbs fit the K8 rubbers snuggly which makes me extremely happy. They are brand spankin new from honda. Well maybe a year old but the point is that they aren't hard as a rock. Its interesting that the F3 model runs 105s because my honda service manual for this bike says it runs 90s....I wonder what else is wrong in this manual. I am running a stock airbox, and K8 points and condensers. I freely interchange some minor parts from my K8 and F3 engines and visa versa. I suspect that the rubber boots on my airbox are shot but I haven't gotten around to changing those. I use a stock filter...I should probably change it but it still looks clean. My timing is spot on when I can actually get the bike to idle at first start up. Today I'm going to take it somewhere to get the carbs. tuned after I determine that the oil delivery is fine. Using the method you mentioned. There are a bunch of reasons why I think this engine was running way lean. For one the valves were burnt...badly and the previous owners where able to get the exhaust pipes cherry red. They had their hands inside the carbs and I don't exactly know what they did to do that. Then the other reason was that the jetting isn't right for the type of exhaust system. I think a 4-1 exhaust sys. requires larger jets. How much larger eludes me but I'm working on that one.

[scondon]

 The main jet sizes will affect how your bike runs at WOT. Changing to larger,or smaller main jets will not have much effect on your mid range or idle. I ran 105 mains on the K8 engine with stock 4-1 F3 exhaust/airbox with no noticable problems. Problems at idle were cleared up by "dipping" the carbs to clean slow jet passages, synching the carbs, and setting the fuel mixture screws at 2 1/2 turns out(stock setting is 1 3/4 turns).

   Getting the exhaust to burn "cherry red" is no easy feat. Ignition timing, valve gaps, open exhaust,missing air filter may have played a role.Since you're only using the engine of the PO I would stick to observing your bikes current running status and do some plug chops to determine how it's burning fuel. You may be much closer to optimum setup than you think.

[Crimson750]

What were you dipping your carbs in to clean the slow jets? I looked at the plugs and the bike is running a touch lean...not bad really. 2 and 1/2 turns on the idle jets is a far cry from stock.

[Lumbee]

I use chem-dip to for dipping, however if the bike runs at idle, then the slow jets are not clogged.  On the issue of engine temperature.  Forget trying to measure temps at the head or exhust.  Just be sure the oil temp is within the correct range.  Take that turkey thermometer you said you have and drop it in the oil tank after the bike gets at operating temperature...it should be 150-180.  Mine usually run around 170.  If any passages are blocked this will cause the eninge to run hot, in turn causing the oil to be hot.  Also like someon suggested removing the tappet covers and looking for oil will do if u'r still unsure.  If u'v been putting miles on it, I'd say u'r OK...a cam or tappet without oil won't last long.  If it hasn't burned up my now u'r OK...

[scondon]

     I use the Yamaha Carb Cleaner(white bottle) available at Yamaha dealers. It is expensive to buy enough to actually "dip" your carbs but it can be used by mixing it with gas and let sit in your float bowls overnight(instructions on bottle). This does a fair job of cleaning the jets.

     The 1 3/4 turns out is stock setting for the F3 carbs and the screws measure fuel with air as a constant These are the carbs with screw on float bowls and the mixture screws that points straight down and are a #$%* to adjust on the bike without the correct tool. Setting these at 2 1/2 turns out is not a great leap since 1 3/4 turns is LEAN. The other carb types(clip mount float bowls, mixture screws pointing out sideways) have a starting setting of 1 turn out and turns of 1/4 in or out may have a big effect.These screws measure air with fuel as a constant. Still not 100% certain which type carbs your running so don't want to give any bum advice.

[Boomologist]

As for the cam towers not getting oil, you would know that it wasn't in the first 20 miles or so. I had that experience. The engine squealed a couple of times real fast and locked up solid. Couldn't kick it or use the electric start. Let it set for an hour and it loosened up and rode it home.

The oil in the tank on my chop gets uncomfortable hot on my leg when at a red light if it's above 80f out.

[Crimson750]

Well, I was on the bike for a good 3.5 hours and and about 50 miles around trip ride. Yeah, at this point i'm pretty sure that the cam is getting oil. I also used the method scondon suggested. So oil i believe isn't an issue. The type of carbs used on my bike are Keishin or keisin. My float bowls are screwed on, not clipped on. Is it normal to have different temperature gradients in the oil tank. After about 1.5 of riding I pulled in and dipped in my temperature probe in the oil and measured 190 degrees F (normal for what everyone is telling me) then when I pulled it to the surface (about 5.5 to 6 inches in length) the temperature jumped to 220 degrees F. I figure the average of these is around 210. So I know th engine at normal running is getting oil that is around 190 degrees and is returning it at around 220. Does this sound right?

[Bob Wessner]

Is it normal to have different temperature gradients in the oil tank.

Convection could account for some the difference also. The hotter oil entering the tank would rise to the top and as it cooled, fall to the bottom.

[MRieck]

I get 180 to 205 with an electronic gauge off off the oil pan. I also run a good size Earl's but I have a large engine. It is tough to get over 200 though even in the 90's here in New England,

[Crimson750]

I figured the temperature differential could either be do to convection or oil being delivered from the pump. I would just really like to have my bike to ride for a bit because I haven't been able to ride it regularly because of various other problems. Having to take the engine out again this summer is going to kill me. I was hoping to put the engine together right the first time so I wouldn't have any issues. Once I get my F3 rebuilt I'll consider putting some money into the one I have in my bike now. I'm still kinda skeptical as to if this particular bike can do wheelies...Although doing stunts on it isn't my plan. Anyway thanks all for the help and have a safe riding season.

[SteveD CB500F]

Probably not relevant (but that's never stopped me before...)  but my the fan on my VFR cuts in at 104C which is 220F. The engine normally runs at 85C (185F)

I can't believe thermodynamics have changed much over the last 30 years.

Or then again...

[Crimson750]

I'm just trying to get a feel for what is normal. I'm still rather new to engine mechanics. This is the first engine I've taken apart, put new components in and get it running. I'm trying to avoid newbie mistakes that would typically destroy an engine.

[Bodi]

On the 400F (460 Yosh kit) I have a thermometer attached to the Lockhart oil cooler, on the return side. It reads 150C on highway runs in hot weather. This is 300F. No problems with the bike, so I presume this is not too hot. I do use synthetic oil exclusively.

[neil young]

if the oil dip stick is so hot that i cant touch it without a rag is this normal  this is after riding about 7 miles not to hard

[Bob Wessner]

if the oil dip stick is so hot that i cant touch it without a rag is this normal  this is after riding about 7 miles not to hard

Are you talking about the cap holding the dip stick? If so, that does seem hot after only 7 miles. If you are talking about the stick portion that is immersed in the oil, maybe not, that can be 180^oF.

[theunrulychef]

Sorry, a little off topic here:

MRieck, is the oil pan the best place to pull temp from?  I'd like to put a temp gauge on my F2, but I've already got a pressure guage in the galley.  Also wondering if it matters where on the oil pan you tap into for the temp sender.

Thanks,
Jay in Philly