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How hot is your engine?

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1967 R502
Posts: 143
Joined: Thu Jan 25, 2018 11:47 am

How hot is your engine?

Post by 1967 R502 »

My R50/2 is running with a sidecar. Came back from a ride today (70F degrees and drizzle, so not a searing temp) and after stopping, my bare hand happened to contact the engine block and was almost burnt.

Now it’s not like I keep a mental log of what my engine temp should be, but that seemed a bit much.

My dipstick thermometer read 120C. Or about 250F

Normal? I have t been running with a sidecar for very long, so while I might expect it to run hot, I just want to have an expectation of what is too much.
Last edited by 1967 R502 on Mon Nov 07, 2022 10:45 am, edited 1 time in total.

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niall4473
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Re: How hot is your engine?

Post by niall4473 »

120 degrees C is not really excessive.
When you say the 'engine block' do you mean the crankcase?
What is your oil capacity, do you have the original flat sump? in days gone by it was common practice to fit extended sumps, partly for this reason, my oil temp gauge on my R69S outfit shows about 90 degrees C after 120+ miles, although the ambient here is about half yours, what gearing are you on?, the 6/26 is a bit too low usually and keeps the revs higher than I like, the 7/27 is usually better if you can find one.
Oil is always cheaper than metal

1967 R502
Posts: 143
Joined: Thu Jan 25, 2018 11:47 am

Re: How hot is your engine?

Post by 1967 R502 »

1. Yes, the Crankcase was hot.
2. Yes I have an Extended sump. This is a mixed blessing at best. More oil yes, but increases the heat swamping once stopped, because of course the engine is on top of a bunch of boiling oil which takes longer to cool down.
3. Sidecar gearing. Forget the ratio off the top of my head.
4. Also had the cylinders nikasil plated on Vech recommdation.

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Flx48
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Re: How hot is your engine?

Post by Flx48 »

Here's another datum-
My rig is a '60 r69 w/spezial, 7/27 rear, carbided cylinders.
On the days we do 100+ miles on the way home, I'll often take the engine's temp when rolling back in the barn.
I take the temp at the heads, I'm not that concerned about the oil temperature, comparative head temps will let me know if I've got an issue.
Normal for this bike is around 240F, measured between the exhaust valve and the exhaust port.
A bit less if just doing local shorter local runs, and a bit higher if a long ride on a hot summer day.

I find the extended sump helpful, it allows for a somewhat larger quantity of oil in the sump-
The primary job of engine oil is of course lubrication, secondary is heat removal, and tertiary is keeping the engine clean.

Hot oil is a good sign it is doing its job, removing heat.
The big sumps are usually cast aluminum, and usually have cooling fins cast into them; these do a much better job of shedding the gathered heat than the stock stamped steel pan.
The difference in heat dissipation between aluminum and steel can be measured at the heads/cylinders.
The cylinders are usually about 10F cooler than the heads when the engine is initially shut down, but within a minute or two the heads are cooler than the cylinders and they continue to cool faster than the cylinders until they both reach ambient temp.
And the tertiary job of oil is keeping the engine clean: the larger quantity of oil is more capacity for further diluting of contaminants in the oil.
The oil, in effect, acts as its own filter; because the s/c rig constantly works harder than the solo bike, I make it a practice to change oil at 800 mile max intervals.
The longer oil is left in the sump, the more contaminates have a chance to be deposited in the slingers.
I view the slingers as oil distributors, not oil filters; that slingers also act as filters is by default, and not design.

You may want to calibrate your thermometer, if that hasn't been done recently, just for a base line.
Best-
George

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