If you like our site, please consider joining our club!
By joining you will help ensure that we can continue to provide this service
JOIN HERE!

R75/6 engine / Oil temp

User avatar
schrader7032
Posts: 9016
Joined: Fri Oct 27, 2006 3:00 am
Location: San Antonio, TX
Has thanked: 2 times
Been thanked: 29 times

Re: R75/6 engine / Oil temp

Post by schrader7032 »

I've always added 1.0 to the compression ratio to account for the basic atmosphere, so 10x14.7. I've always thought that an R100/7 would be in the 150 psi range.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

Andey
Posts: 117
Joined: Wed Sep 02, 2020 12:45 am

Re: R75/6 engine / Oil temp

Post by Andey »

cbclemmens wrote:
Tue Sep 06, 2022 12:07 pm
Andey;

The compression test should tell you if your rings are seating or not. My Haynes manual says the compression ratio on an R 100/7 is 9.0:1. 9X14.7=132.3. You should get +/- 130 psi on your compression check. If you have less than 120 psi something is leaking, either rings or valves. But if your compression is good then you have to look somewhere else for your problem.

Craig
Hi Craig, thanks for your reply.

Yeah I haven’t actually gotten around to do a compression test. I really should get a new compression tester and try it.

I usually do a leak down test on other engines (using other methods) and if they pass, usually they run amazing.

But the cylinders both failed the leak down test this time, attached to the engine and I was hoping to check on the bench to see if they pass the rebore and oversized piston rings.

But I realised I can’t do the test on the bench because of the pressures on the piston will just pop them right out.

I was doing the test wrong anyways with the cylinders on the table.

I’m about to reinstall everything and test it out properly

Andey
Posts: 117
Joined: Wed Sep 02, 2020 12:45 am

Re: R75/6 engine / Oil temp

Post by Andey »

So ended up doing 2 rookie mistakes this time around:

1. After I put the last top end together and installed the exhaust. 2 screws left to tighten before firing her up. I look towards the parts box and lo and behold, I see a piston circlip… forgot to install the circlip to hold the pin in… reversing 4 hours of slow work… back to the start of the day

2. This one I’m not proud of, and definitely not very characteristic of me. After installing the circlip and I fire her up… sounds great… no smoke, carbs need a bit of adjustment, but all pretty good. Switch the engine off, and leave it to the next day to tune and test ride. Come back the next day to go for a short run, hoping to just re-adjust the carbs. But the left cylinder isn’t having any of it… plumes of white smoke from engine start to idle.

I’m thinking, “oh that’ll clear up…”. After about 5mins of idling, something isn’t right still, never mind I’ll ride down the road. Still smoke… push the bike home scratching my head.

Doesn’t make sense it’s only happening to one side only, the rebore happened to both cylinders. I must have put the oil scraper ring on upside down! Took the cylinder apart again… and I see the 1st compression ring was upside down… the rest of the rings were fine.

Button her back up, 3 hours later it’s started and back to normal… rebalanced the carbs and ready for its run in period…!

User avatar
srankin
Posts: 1054
Joined: Fri Jul 14, 2017 8:45 pm
Location: Spencerport, NY USA
Been thanked: 14 times

Re: R75/6 engine / Oil temp

Post by srankin »

Believe me, I learned the hard way, LOL. Nice progress on your part. St.
Owner of a 84, R80RT and 78, R100RS

Andey
Posts: 117
Joined: Wed Sep 02, 2020 12:45 am

Re: R75/6 engine / Oil temp

Post by Andey »

Just happy to hear the engine start again.

There was something I noticed though, the oily piston still exists… no smoke, so I’m thinking is it the type of mineral oil I’m using in the crankcase?? It just leaves a sheen on the pistons…

It is 20w50 mineral oil… wonder if it’s a problem.

The oil filter didn’t look bad when I changed it after about 1000kms

User avatar
srankin
Posts: 1054
Joined: Fri Jul 14, 2017 8:45 pm
Location: Spencerport, NY USA
Been thanked: 14 times

Re: R75/6 engine / Oil temp

Post by srankin »

Remember what I have said, there has to be some oil getting past the rings to lubricate them.

I would worry if you find your spark plugs after a good long ride are black, or black and oily, or if someone is following you and sees smoke, or you are using a lot of oil.

if your compression is now good, a leak down good, not much to be concerned with. Enjoy the riding. St.
Owner of a 84, R80RT and 78, R100RS

Post Reply