Honda XR80 / XR100r

[texscottyd]

Ha!  A BMW and Rotax partnership... what could possibly go wrong?   🙄

I will say that the Rotax V-twin in my Aprilia RSV-R has been remarkably reliable over 25K miles of pretty aggressive use.  Parts availability is becoming the limiting factor on these older bikes at this point... 

[knyte]

Agreed, on all counts.

This one has over 130,000 kms and it seems like the valve seats are failing.  Not bad, all things considered.  Just really tricky to diag that - had to outsource this piece.

[PhotoAl]

8 hours ago, knyte said:

I bet you wouldn't say that about a certain '03 BMW F650GS I know, haha...those Rotax engines are unlike any other when it comes to maintenance and troubleshooting, SHEESH!!

I had a BMW F800GT with the Rotax twin.  It was pretty reliable, i had it to 32,000 miles with no issues.  Dealer did all the service.  LOL remember I picked it up from the 2nd valve adjustment, tech mentioned the exhausts were set too tight.  He wrote down the before numbers for me.  I looked up specs and yup exhausts set to intake specs.  Service tech at 1st service obviously messed up!  They are difficult to fill with coolant - need to be vacuum filled and have a funky oil sump setup.  I love my CP3 🙂

[knyte]

3 hours ago, PhotoAl said:

They are difficult to fill with coolant - need to be vacuum filled and have a funky oil sump setup

Yep, this one too.

And, nk, CP3's are a treat to maintain compared to some bikes.

[skipperT]

14 hours ago, knyte said:

BBR says the stock breather is fine up to 120cc, which this is now.

 

It's black, but I'm sure it's oil because I installed smaller jets (one size down from stock - BBR recommends one or more size up, but I'm at a bit of altitude) and leaned out the mixture screw to 1 turn out (stock is 2 3/4 turns out).

The plan is to pop the jug off and try something different with indexing the rings.  I noticed a puff of air from the oil filler tube last night when pushing the kickstarter down, so I'm 99% convinced I've screwed up the ring indexing.

If you noticed a puff of air from the crankcase, then some of the compression pressure is escaping past the rings and blowing back into the crankcase. This suggests improper sealing, caused by too big piston to cyl clearance an/or faulty rings  

Ring end gap should have been checked and adjusted if necessary. Cyl should always be cleaned before assy (right out of the box they usually still have machining oil and grit left over which will ruin a new set of rings).  Rings rotate as the piston goes up and down, so I wouldn’t be as concerned with the indexing of the gaps (usually 120 degrees apart) as I would that the rings are installed correctly (markings facing up, compression and second ring in the correct spot, expander and oil rings installed correctly. )

To diagnose this correctly, measure the piston and cyl, calculate the clearance, and also install the rings into the cyl and measure the end gap. Make sure the piston was installed correctly so that the arrow or marking faces the exhaust side. 

I hate to say it, but once you tear it back apart you will probably find something that will need to be replaced, and then re-installed correctly for proper running. 

-Skip

[knyte]

8 hours ago, skipperT said:

compression pressure is escaping past the rings and blowing back

My thoughts exactly

 

8 hours ago, skipperT said:

Ring end gap should have been checked

BBR says this isn't needed, because it's a complete kit, made to spec.

That said, it's worth a check, for sure.

8 hours ago, skipperT said:

Cyl should always be cleaned before assy

Yep this is part of the instructions / assembly process.

8 hours ago, skipperT said:

so that the arrow or marking faces the exhaust side

Now this part was NOT mentioned in the instructions - anywhere.  The factory piston does have a marking on it, but the BBR does not.  I accidently found a vid where someone just randomly mentions one valve cutout on the new piston is larger than the other, and to orient it correctly.  I honestly hadn't noticed this - they looked identical to me.  Anyway it's something I'll absolutely be looking at.

8 hours ago, skipperT said:

you will probably find something that will need to be replaced, and then re-installed correctly for proper running

Apparently a somewhat common issue is the scraper ring can fold over.  I don't think that happened, but I do suspect the corrugations may have overlapped when the ends should butt up against each other.  It's not easy to ensure this during assembly.  I'll just have to try it again

Thanks for your thoughts...this is all valuable stuff

[texscottyd]

@knyte - Any update on this?   Just curious what you found… 

[knyte]

Been on vacation / away from the house for better than a week.  The plan is to tackle the XR this week.

Thanks for asking!!  ...will def post results when the time comes.

[knyte]

Quick update on this project.  After much messing about with no results, I finally ordered a bare head and valves.  The BBR kit already has everything else; springs, keepers, seals, cam - so I hope to wrap this up this summer.

The hardest part(s) to find are plastics, specifically the side shields.  Very hard to find.