Need advice on Top end/motor rebuild

[dre]

I have a 75 R90/6 with about 36k miles that needs to have some engine work done. I've had a local shop in LA take a look and has recommended a full rebuild of the motor.

What questions should I be asking to be shown that all of these need/should to be replaced?

I'm also trying to separate parts from top end rebuild and bottom end rebuild.

Anything I should consider doing as an upgrade? He has noted a 336cam, but everything I've read means there are additional items needed for it to work (dual plug heads, 40mm carbs, etc.)

Below is the work order and parts list:

1. Cylinder heads need to be rebuilt
2. Cylinders in spec, need minor hone on cylinder walls and new rings
3. Needs all new bearings, mains, and rods
4. Polish crank
5. Timing chain and sprockets
6. Full engine gasket kit

Parts list
ENGINE REBUILD GASKET KIT 11 00 1 255 023
HEAD Valve Guides
HEAD Valve Springs 11 34 1 263 873
HEAD VALVE JOB valve grind/seat angle - grind and dress valves-install new valve guides. ream to spec - blast and decarbonize ports. face heads
HEAD SPARK PLUG INSERT - ANTI corrosive insert included CAMSHAFT TIMING GEAR CRANK 11 21 1 250 198
CAMSHAFT TIMING CHAIN 11311250258B
CAMSHAFT TIMING GEAR CAM 11 31 1 250 253
CAMSHAFT TIMING CHAIN TENSIONER 11 21 1 265 455 CAMSHAFT TIMING CHAIN TENS SPRING 11 31 1 253 188 CRANKSHAFT GROOVED BALL BEARING 07 11 9 981 722 CRANKSHAFT BEARING SHELL 11 24 1 258 460 (set of 4) CRANKSHAFT BUSHING STANDARD 11 11 1 250 155 (set of 2)
RING SET - 2ND OVER -
11 25 1 259 855 SET: REPAIR KIT PISTON RINGS -
+1,00.10
CYLINDER HONE - clean up only. - machine shop.

Crankshaft Sprocket Duplex 1121198
Camshaft Sprocket Duplex w/tachdrive 1131253
Bearing Shell Conrod R2V 1124460
Conrod Screw R2V 1124553
Ball Bearing for Crankshaft, front 7711722
Duplex Timing Chain w/ Master Link 1131258
(Optional) Camshaft 336Degree 1131053

[Kurt in S.A.]

Wow...that's quite a list. My first thought is...get a 2nd or 3rd opinion. I would certainly want to know what info is telling them that a 36K miles bike needs a complete overhaul. Sounds a bit fishy to me.

You need a good compression test and a leak down test. A top end can't be determined until the pistons are moved and measurements are taken of the rings and cylinder bore.

What is telling you that work needs to be done? Burning oil? Poor gas mileage? Other performance problems?

Kurt in S.A.

[jagarra]

36k is nothing, as Kurt asked what are the symptoms that caused you to bring to a shop in first place.

[dre]

I purchased the bike used through a friend that has a shop, it was from a former client of his who bought it used off of craigslist. It was purchased with the intent to strip down and cafe it. They ran it a few times while it was sitting in their storage. It was smoking a bit and had a leak, so they diagnosed a top end problem. Since they don't normally work on BMW, they recommended another shop that does BMW builds for the motor work, he opened her up and came back with the following.

So there is a top end issue. Cylinders were measured. I need to see why they're going to a 2 over hone, wouldn't 1-over be first step after stock? I'm going to have to speak with him at length to go over what items are necessary, and what is optional.

[SteveD]

You need a third opinion. Blowing smoke is usually just worn valve guides. The smoke is easily seen after accelerating from an idle, eg taking off from traffic lights. If the car behind has it lights on, at night, it's very easy to see the smoke in your mirrors.

[Airbear]

Something is definitely wrong there. Specifying 2nd oversize rings but only a cleanup hone for the cylinders implies that the engine has already had two rebores, or something equally weird. At 36k this is most unlikely.
And a complete bottom end rebuild at this mileage is very unusual. Bottom ends are very robust. Buying all the parts they specify plus the labour cost will be crippling.

I would want the mechanic to show evidence of whatever terrible disaster has happened and show examples of the damage to those engine parts.
If something catastrophic has happened - run without oil, or a nasty bit of metal has found it's way through all the bearing shells - I would be looking at a used short or long motor, depending on the extent of damage. Don't feel obliged to go with that shop. You can come to some arrangement for their time and retrieve everything if you have any doubts.

Are you mechanically inclined, have workshop space and tools?

[dre]

Thanks everyone for the info. I'm going to try and swing by today and get shown what needs replacement and why. Does anyone have any shop recommendations in the Southern California area? That I could take it to for a second opinion?

[Kurt in S.A.]

Irv Seaver's in Orange

Dave Campbell's in Santee

Kurt in S.A.

[Ken in Oklahoma]

Something is definitely wrong there. Specifying 2nd oversize rings but only a cleanup hone for the cylinders implies that the engine has already had two rebores, or something equally weird. At 36k this is most unlikely.
And a complete bottom end rebuild at this mileage is very unusual. Bottom ends are very robust. Buying all the parts they specify plus the labour cost will be crippling.

I would want the mechanic to show evidence of whatever terrible disaster has happened and show examples of the damage to those engine parts.
If something catastrophic has happened - run without oil, or a nasty bit of metal has found it's way through all the bearing shells - I would be looking at a used short or long motor, depending on the extent of damage. Don't feel obliged to go with that shop. You can come to some arrangement for their time and retrieve everything if you have any doubts.

+1 on all the points you make. I'm very suspicious about a mechanic recommending bottom end work. Nobody I know has had to rebuild their bottom end. (Uh, I guess I should have said their BMW's bottom end.) Head work, perhaps, but I would want to see the evidence of the need first. But even then airhead head work I would farm out to a known experienced head mechanic. (No pun intended--I wasn't even tempted).

Ken

[tsa]

I have a 75 R90/6 with about 36k miles that needs to have some engine work done. I've had a local shop in LA take a look and has recommended a full rebuild of the motor.
. . . .
Anything I should consider doing as an upgrade? He has noted a 336cam, but everything I've read means there are additional items needed for it to work (dual plug heads, 40mm carbs, etc.)

+ 3 (or more) on the very good advice you've got so far.

A few more comments; if it has 36 KMi on the clocks it doesn't mean that's how many miles the engine has done. I suspect you have no service history for it?

Re upgrades, an R90/6 doesn't need a hot cam, twin plugging or 40 mm carbs to run well. Before thinking about that, I'd consider a pair of used good R100 barrels/pistons instead, they should bolt straight on (unless yours is a VERY early one, with 97 mm crankcase openings!) and give a bit more "grunt" (= performance where you need it). If I wanted more power, I'd buy an oilhead R1100 boxer.

Without any service history, and a likely higher mileage than the clocks suggest, do also take a look at the bevel drive splines, and the condition of the gearbox. Both may need attention.