R75/6 engine / Oil temp

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Andey
Posts: 77
Joined: Wed Sep 02, 2020 12:45 am

R75/6 engine / Oil temp

Post by Andey »

Hi all,

Andey here again, it’s been a while since logging in.

Straight to the point, how hot should the engine (looking more at the crankcase, rather than cylinders) be running at? I know we cant gauge the engine itself, so should I be looking at the oil temp?

I might be imagining it, but the crankcase seems to be a lot warmer than the cylinders at a medium powered run out… nothing like 80mph.

Of course the cylinders have the fins, but I always remember it being around the same temp as the crankcase and vice versa…

I’ve been reading that it should be around 220-260F, or is that just everyone says?

The bikes been riding great, slowly taking her further out, but still need to overhaul the gearbox at some point, most likely will happen in the next 2 months or so and will redo a compression test.

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schrader7032
Posts: 7806
Joined: Fri Oct 27, 2006 3:00 am
Location: San Antonio, TX

Re: R75/6 engine / Oil temp

Post by schrader7032 »

I think your number is in the ball park...maybe closer to 200-230F would be a good operating temperature and I'm speaking of the oil...not sure about the case. I suppose you could get one of those cheap infrared temp readers and take some spot readings around the bike just to get a baseline.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

Andey
Posts: 77
Joined: Wed Sep 02, 2020 12:45 am

Re: R75/6 engine / Oil temp

Post by Andey »

Good to hear from you Schrader, hope all’s well!!

I’ll take it for a few more rides and see if anything changes…

I’ll shoot it with a temp sensor after the ride to see if there’s any insights that way…

I did get a cam down the pistons and I’m wondering if the cylinders are passing oil past the rings…

Is that too much carbon build up on the exhaust valve side? It’s been about 800kms since I had the heads off
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schrader7032
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Joined: Fri Oct 27, 2006 3:00 am
Location: San Antonio, TX

Re: R75/6 engine / Oil temp

Post by schrader7032 »

I'm sure someone has more experience in reading the tops of pistons that I do. There is going to be some oil getting by the rings if you're still in the break-in process, which at 800kms sounds like it...I'm assuming you replaced rings then. Rings have to seat plus there's a way to orient the three rings to minimize seepage. But I don't think it's an exponential build up in the chamber...I'm sure it stabilizes as some point unless you have way too much oil usage which you would soon know if you see smoke from the engine and/or you have to put a lot of oil in.

Here's a picture of my left cylinder after about 90K miles. It's certainly covered in build up but I don't think it was excessive. If you do get excessive build up you'll begin to hear pinging when you had not before.
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LeftGasket.jpg
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

jimcarrr100rs
Posts: 14
Joined: Sun Oct 13, 2019 2:47 pm

Re: R75/6 engine / Oil temp

Post by jimcarrr100rs »

Your piston looks wet in the picture. It should be dry like the other picture.
77 & 83 R100RS, 56 R69

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