1987 R100RT overhaul

[atle]

Hello everybody,

I thought I had been a member of this forum before, but I couldn't find my previous posts (from a couple of years ago), so I registered again.

The story goes like this:
I bought a 1987 R100RT four years ago and left it in the garage the entire time. I haven’t used it much, except for a short ride during the first year, when I noticed the motor ran a bit rough. Since I don’t have the bike's full history, I’ve been thinking about doing an overhaul before I start using it regularly.

Now that I’ve started tearing it apart, it’s clear that it has been worked on before. While this might not necessarily be a bad thing, I’d like to figure out exactly what modifications have been made and which ones are beneficial—or not so great.

So far, I’ve discovered the following:

The bike is registered as a 1989 R100RT, but the serial number indicates it’s actually a 1987+ R100RT.
The cylinders have been replaced with a Siebenrock set. I contacted Siebenrock, and they confirmed that the labels “10” and “S” indicate a Replacement Kit Extra 1000cc. I assume the entire kit was replaced, but I’m not entirely sure.
Can I remove the heads for cleaning and inspection without removing the cylinders, and then remount them and torque them to spec?
The heads have dual spark plugs. I don’t know if these are the original heads that have been machined for dual spark plugs. Is there any way to measure the heads to confirm their size? Did the heads originally come in different sizes with varying valve sizes?
The carburetors are 40mm with a needle jet of 2.66 (94/40/111 and 112). I think the stock carburetors on an R100RT are 32mm—am I correct? Will the bike run okay with 40mm carbs?
There’s also an external oil cooler installed.
Does anyone have suggestions? Should I just replace all the gaskets, O-rings, and fluids, and give it a try, or should I consider changing something else?

Best regards,
Atle

[atle]

Before and now

[melville]

Where are you located? US market 1000cc Monolever bikes should all have 32mm carbs. That said, the heads for 40mm carbs are slightly different and it's possible that along with the dual plugs the PO wanted to make some mods.

I have an R100/7 with 32s and an R100RS with 40s and I actually prefer the 32s on a touring bike. My R100/7 has the full vintage touring kit with big Luftmeister fairing, bags, backrest, and Russell Day Long seat and I like the way it pulls from a standstill with a pillion on it.

The RS with the 40s is softer at low revs but pulls harder from cruising speed. And probably goes a lot faster on the top end, but that stuff is strictly academic.

[atle]

Hi,

Thank you for answer I’m located in Norway.

If I understand you correctly the 40mm carbs require different heads than the 32mm ? Is the different carbs matched to different heads?

[Rob Frankham]

The bike is registered as a 1989 R100RT, but the serial number indicates it’s actually a 1987+ R100RT.

Not unusual. vehicles frequently stayed 'in the system' for one or more years between date of manufacture and date of registration

Can I remove the heads for cleaning and inspection without removing the cylinders, and then remount them and torque them to spec?

Yes.

The heads have dual spark plugs. I don’t know if these are the original heads that have been machined for dual spark plugs. Is there any way to measure the heads to confirm their size? Did the heads originally come in different sizes with varying valve sizes?

Valve sizes differ for model and year. a monoshock R100 should have 42mm inlet and 40mm exhaust. About the only sensible alternative is the 44mm/40mm used on most twindhock 1000cc models. If the heads were replacements from Siebenrock, then they are probablyt not the originals. I don't know what valve sizes they supplied in their kits.

The carburetors are 40mm with a main jet of 2.66 (94/40/111 and 112). I think the stock carburetors on an R100RT are 32mm—am I correct? Will the bike run okay with 40mm carbs?

According to the books, the monoshock R100RT was fitted with 32mm carbs although there are many reports of them fitted with 40 mm instruments. The R100GS still had the 40mm carbs so it is likely that the bike will perform pretty well with them. It may be that the substitution was part of the 'Siebenrock' upgrade

There’s also an external oil cooler installed.

Oil coolers (stock ones anyway) can be a PITA and they are almost certainly not needed (especially in Norway). However, they are also a real pain to remove requiring the replacement of the centre spigot in the oil filter to do the job properly anyway). Best left alone, at least for now.

Does anyone have suggestions? Should I just replace all the gaskets, O-rings, and fluids, and give it a try, or should I consider changing something else?

My approach would be to change fluids and check for obvious leaks then run the bike (with due regard for unusual noises and etc.) Watch out for any leaks and if necessary fix them but don't undertake a full refurb until you have some knowledge of how the machine is running. Make a list of things that need attention then take the machine off the road and tackle them all.

After 4 years laid up, the tyres are probably beyond their best.

Rob

[atle]

Thank you very much for the answers.

I think I will take off the heads and inspect them. I remember the bike ran rough the last time I used it, and the spark plug is now very black and sooty, so it looks like the mixture is too rich.
Regarding the oil cooler, the connections are rusty, and I would actually like to get rid of the whole thing. It looks ugly and blocks easy access behind the front cover.
I noticed that the cost of a new oil filter tube and cover is not much (less than the cost of new oil hoses for the rusty cooler), so if it’s not needed...
For the future, how is an oil pan extension as a solution?

And the tyres... way overdue! produced 2012....

[Kurt in S.A.]

An extension on the oil pick up and larger pan is typically done for some extra cooling. Since you're in Norway, it's not really needed.

Kurt

[Rob Frankham]

No need for an oil pan extension. The '87 models have a deep oil pan anyway. The extensions were produced mainly for the pre '80 machines which have a much shallower sump and arguably they gave some advantage... although it's debateable whether they are needed in temperate climates.

If you want to renove the oil cooler, well and good but be aware that the central tube may not come out easily... You will need a special tool to shift it anyway.

You can't take any inference from black plugs on an engine that has been standing for 4 years. Run the bike and tune it. It's highly likely that the 'rough running' can be tuned out. In any case, do a compression test (or better still a blow down test) before stripping. It will give you a great deal of information about what to expect.

Rob

[atle]

It looks like I went a bit further than I originally planned... Now, I will measure all the parts and check if any bearings or crankshaft thrust washers need to be replaced.

Overall, I think everything looks quite good.
I am trying to identify the crankshaft thrust washers by the numbers stamped on them. The color (if there ever was one) is no longer visible.

The inner crankshaft thrust washer is labeled 1256974,9, and the outer one is labeled 1256975,9. I don't understand what the ",9" represents.
It seems (based on BMW part numbers) that 1256974 corresponds to a blue thrust washer and 1256975 to a green one.
Anyone know?

IMG_4009 (1).jpg (1.43 MiB) Viewed 828 times

[Rob Frankham]

Before even worrying about the size of your existing bearings, I would check to see if the end float of the crankshaft is out of spec. These bearings seldom give problems unless they are damaged by carelessness or lack of maintenance.

Assemble the crankshaft into the crankcase with the thrust washers in place. Fit the flywheel and use a dial gauge to measure end float. This should be between 0.08 and 0.15mm. If it is, reassemble the engine and forget it...

If it isn't, you need to check the thickness of the existing bearings. The sizes should be...

1 256 973 - red - 2.483 to 2.53 mm
1 256 974 - blue - 2.53 to 2.578 mm
1 256 975 - green - 2.578 to 2.626 mm
1 256 976 - yellow - 2.626 to 2.673 mm

Wear limit is 0.2 mm

Now you need to sit down with a piece of paper, calculator or computer depending on how old you are and use the exisitng end float, together with the actual thickness of the existing bearings to decide which combination of bearings will give you a float in the correct range.

It's not advisable to use an out of spec existing bearing, even if you can achieve the end float spec because the bearing surface will possibly fail.

Hope that helps...

Rob