Bmw r75/5 microsquirt project for a newbie

[fefenin]

I would say it is lack of oil damage I didn't have any light for oil before...But I didn't remember running no oil at all or somebody didn't fit the proper before me, my dad rebuilt the thing 15 years ago. Could be knocking as well cause I came back hope with a bad capacitor/ points that was painfull for the hears.I ll try the close up on day light soon. For now here is another. It seams this is not flat on one edge.

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[R100RT]

I'm afraid to say that I would suggest your bottom end looks worthy of a rebuild. This is a tough thing to offer, as it comes with many highly technical procedures that aren't that bad if you had the shop, tools, and patience - but would be pointless if not.
Not sure what your shop situation is, and you may have no interest in such an investment when a good used short block might be reasonable money.
I tend to recycle anything that has a remote hope of living again, or morphing into something else on a project - so perhaps don't listen to my advice on this one

[fefenin]

I am really OK to rebuild it but how ?

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[R100RT]

Maybe "Yes", maybe "No" - all I'm saying is that what I can see through your photos tells me I'd continue forward inspecting things, measuring things.
Do you have someone who can assist you with the areas like precise measurement, parts cleaning, and to some extent special tools? What I can perhaps suggest also, is that we could do a search on ADV to see if there are any fellow BMW enthusiasts in your general area that might lend a hand.
This is not to suggest you are not able to perform the work - I'm just being cautious and ensuring you don't gain false hope on the situation if it is repairable but you don't have the resources to take it on.
Trying to be what we are renowned for being - a polite Canadian

[LAV1000]

Hello there fefenin,

Man you got a lot off trouble
I am stil reading your posts, and seeeing the mess.
Wich reminds a comment on your post at 12 may 2016.
Did look at the pictures again and it occured to me that there is rust on the crank bearing.
And also the tension spring on the camchain, looks like it is installed the wrong way, check your manual on this.

I don't know beemers but is it possible/done to regrind the crankshaft and use oversized bearing shells.
It is common practise on car cranks.
You need a specialist to regrind your crank it is not DIY job.

If you put things together again check the oilways for obstruction.

Good luck whit it you need it !!

[fefenin]

The timing chain spring is done the right way according to the manual

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[R100RT]

If your low oil pressure light comes on when you had first turned ignition on/ bike off, then goes out as it starts - and doesn't come on at idle even hot - then generally the relief valve, and the cam tension spring are in place. The oil filter on these engines requires a bit of care to ensure the designated cover "O" ring, and depth shim is maintained. Generally, if everything that was used previously is carefully viewed during disassembly, and then reinstalled in same order you are safe from low oil pressure issues. I believe you have some wear showing in the one photo from the timing chain having slopped about but wasn't that from the original worn item?
As previously mentioned in this chapter of your adventure here, the servicing of these boxer crankshafts is "significantly" not routine regrinding work due to the need to remove and reinstall the counterweights - many shops can't seem to get the rivets stabilized and things come flying apart at high revs .

Jeremey - do you have the ability to chat through private messaging on this site? I've sent you some and not heard from you. (Thinking to avoid choking this forum with rebuild chatting - although not entirely sure how much that bothers the moderators). I note you are using a phone most of the time. Let me know, as I have other parts news, and questions.
Regards, Lorne

[R100RT]

Another long post here.
Summary of comments and advice developing over on ADV Airhead forums (where I've posed questions on your behalf )
Suitability to repair is suggested.
- You should pick up a manual that covers your engine design, a Clymer's or similar.
- If low oil pressure is suspected as a potential reason for the failure, pull your oil pressure sender off the block (down on the left side adjacent to frame) and rig up a little pressure test on it with something like the "Mity Vac" or a shop air regulator that can be adjusted to provide air from nothing up to full) and using your multimeter, see if it sends the low pressure message when in fact pressure is low. I would have to look up the set point, can do tonight and post. We are assuming the reason for failure is something that doesn't still exist on your engine - hence it can be safely repaired without concern for another immediate failure and drain on funds .
- Appearance of rod journals is not bad at all. Most agree that you could attempt a lower cost overhaul by taking careful micrometer (or caliper) measurements with the crank still in the case. This is challenging but doable and confirms if there is excessive wear, taper (or slant as you mentioned), and if within the broad tolerances permitted then a polish job could be attempted.
- Polishing can be performed on this "assembled" boxer crankcase by the "shoe shine" method of working emery cloth (about 800-1200 grit for final) around the journal in a see/saw back'n forth manner while the crank is repositioned to allow all sides to be covered. After a finer appearance is gained the entire block can be rinsed with brake clean and air pressure or solvent, plug the oil feed hole in the journal with a bit of rag that is removed afterwards.
- Based on the condition of the oil pressure sender, the oil pump rotor and ring should be checked/ measured with feeler gauges. These items are replaceable - See Motobins in the UK. for better $$.
- A flush of the entire case and crank while together with light oil fed into the oil pressure gallery while turning crank would ensure a clean starting point without a full strip down. The idea here is that if the rod journals measure out okay, and polish nicely, then the condition of the main journals and shells will be okay as they are more of a priority feed point in the oiling circuit.
- The connecting rods can have their big ends resized by a competent machine shop. A slight amount of metal is removed between cap and rod, then when torqued together the original size is honed back into the opening for a nice tight home for the new rod bearings.

So, there you have it - if you feel like going down that avenue. If you don't have the place to do that, tools, or time then you may end up going for a replacement short block but the funds will bee more.

[fefenin]

I will try to do what you say but I still would like to remove the crank ;) sorry for my short answer I will try to do longer later

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[fefenin]

Will that be OK ?

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[R100RT]

Very Good - you have what appears to be a suitable manual. If you are in doubt about something it says, just post questions or seek alternate internet data.

[fefenin]

Thank you very much. Just have to find a way to remove that gear to remove the broken screw. One of my friends might be able to inspect the crankshaft then

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[fefenin]

Lorne sorry to ask but there is something I don't really get... The oversized bearings , are they for the crankshaft or for the rods ? If I grind the rods and the shaft will it work?
I don't really get that yet

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[R100RT]

Oversize bearing shells are used to offset material ground from the rod or main journals of a crankshaft. (& this is not recommend for an airhead crank due to grinding complications and failures/ short re-assembly life)
For your connecting rods, if the crank journals measure OK and can polish clean up, then stock bearings are used with "Resized" rods. That is a process where a machine shop accurately grinds a small amount of material from the rod big end "Joint" surfaces ( where the cap meets the rest of the rod). Then with cap torqued in place the original diameter surface is honed back into it (look up Sunnen Rod Honer) now the standard rod bearing will be at home again in a very tight and acceptable opening - your rods are almost guaranteed to be stretched and have loose holes which would kill new bearings.
I will mention "Oversized Bearings" which is totally different - and refers to the outside of the bearing being made larger.
Those are used when you have to machine a larger bore for perhaps main bearings that have spun in there bores. Quite different.
This is simple however for your situation - in order to be able to successfully rework your sick R75/5 engine, the crankshaft must have its rod and main journal measurements fall within the tolerances hopefully listed in your manual & which will require standard bearings for reassembly.
Hope that helps,
Lorne

[fefenin]

I ask that because motobins sells oversized bearings for the rods. But I see now how you can tighten up the bearing on the crankshaft by grinding the cap of the rods. Really have to do those measurements quick then !

Thanks it is very clear

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[R100RT]

Some examples of "Out of Case" crank polishing by hand:

Crank before.JPG

crank after.JPG

Crank polishing.JPG

[fefenin]

Ok finally managed to remove that .... Screw.
Back bearing

Front bearing

Inside back thrust washer

Outside back thrust washer

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[fefenin]

There is a dent a scratches on one of the crank journal

How do i know if it is too much ?

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[R100RT]

On the photo of the front crank journal, with those "swirled" marks - can you explain if you know how those got there? And are they pronounce by the act of photography or are they as bad as it looks?
The answer to your question is that accurate micrometer measurements need to be recorded on all journals from several angles.
These cranks do not do well if they are ground so hopefully your measurements will be acceptable and that swirly mark only on the surface. Then polish things up and flush everything & rebuild.

[fefenin]

Hello just saw your private mail. No time yet to check it properly. For the marks I cannot feel much with the nails. But there is a dent coming from the broken bit of one of the half rod bushing shell.
So the picture is not showing well everything. It is worse !!!

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