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Topic-icon 1971 R75/5 engine siezed

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2 weeks 1 day ago - 2 weeks 1 day ago #5314 by Chapster70
1971 R75/5 engine siezed was created by Chapster70
Welcome Aboard !!

The seizure is a symptom of the problem. If you don't want to spend a lot of money just to have the same thing happen again, then your job is to find out "Why?"

You have to assume that only one thing goes wrong at a time. This "one thing" may have many symptoms, but it is singular. So I assume your pistons are all scored up and have metal transferred to the cyl walls. That could be a timing issue, carb issue, or a lubrication issue. (BMWs rarely have cooling issues, for obvious reasons.)

One of the wonderful things about a BMW is that you can pull the rods without opening the engine. I would pull the oil filter and then the rods looking for signs of no lubrication. If there is oil in the sump, and everything else looks good, then we'll be looking for other things once the engine is together.

These days it's cheaper to buy a set of cylinders with matting pistons rather than fool with boring the old cylinders. Look in our AirBazar forum for used R75 parts.

When the top ends are all back together with NEW push rod tube seals, then we can look at the timing and carb issues.

All the best.
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2 weeks 1 day ago #5316 by Wobbly
Replied by Wobbly on topic 1971 R75/5 engine siezed
Welcome Aboard !!

The seizure is a symptom of the problem. If you don't want to spend a lot of money just to have the same thing happen again, then your job is to find out "Why?"

You have to assume that only one thing goes wrong at a time. This "one thing" may have many symptoms, but it is singular. So I assume your pistons are all scored up and have metal transferred to the cyl walls. That could be a timing issue, carb issue, or a lubrication issue. (BMWs rarely have cooling issues, for obvious reasons.)

One of the wonderful things about a BMW is that you can pull the rods without opening the engine. I would pull the oil filter and then the rods looking for signs of no lubrication. If there is oil in the sump, and everything else looks good, then we'll be looking for other things once the engine is together.

These days it's cheaper to buy a set of cylinders with matting pistons rather than fool with boring the old cylinders. Look in our AirBazar forum for used R75 parts.

When the top ends are all back together with NEW push rod tube seals, then we can look at the timing and carb issues.

All the best.

Don't hide 'em, Ride 'em !!
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2 weeks 11 hours ago #5322 by Chapster70
Replied by Chapster70 on topic 1971 R75/5 engine siezed
Thank you for the info. I’m not in possession of the bike yet but will be getting it soon, (I just recently was able to look at it briefly and see the condition in person), I realize there is a lot to figure out.
I just wanted some advice on whether a seized engine is something that can be corrected or if it’s a huge rabbit hole.

Found these on the air bazaar:
Set of R75/6 cylinders in very good condition. Cylinders, pistons, and circlips included. No rods or wrist pins.

Cylinders were blasted and honed. Standard size. Piston sizing is 81.965 and 81.975. Pistons marked to match original cylinder. Came from a bike having 63k on it.

Will these work on the r75/5

Thanks again
Chapster out

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2 weeks 4 hours ago #5326 by Wobbly
Replied by Wobbly on topic 1971 R75/5 engine siezed
Any motorcycle that's 40 years old is going to have lots for you to figure out. At least with this one, you'll have an opportunity to put it together right and then the nagging devil of "it's not going to make it" won't be in your ear every time you get more than 1 block from the house.

Others may answer, but I do believe the cylinders are the same for all R75's. Cylinders and mated Pistons is all you need. Along with all new gaskets, you'll also want new push rod tube seals and new rings. If you pull the rods, then you'll want new Std size rod bearing inserts to put it back together with.

Several hours of labor scraping gaskets and such, but technically a very easy job.

Let me re-state my assumption... All this advice is based on piston-to-cyl seizure... Which you have NOT confirmed.

Don't hide 'em, Ride 'em !!
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1 week 6 days ago #5329 by 8053
Replied by 8053 on topic 1971 R75/5 engine siezed
Another thing to consider is that the /6 motors had a change made in the opening of the motor casting where the cylinder fits in the crank case. All /5's and early /6's have a 97 mm opening, and later /6's were enlarged to 99 mm. I'm thinking the change was made for the 1976 model year bikes. It would be best to get a measurement on the cylinders you are considering.

James Strickland, IL. Airmarshal

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1 week 6 days ago #5330 by Chapster70
Replied by Chapster70 on topic 1971 R75/5 engine siezed
I’ll look into the size to confirm they will work. Hoping to pick up the bike this week and have more info in front of me.
Thanks for the advice, I’ll let you know as I progress with the new adventure.

I used to work on the 240 series Volvos and owned 3 of them over the years. They seem similar to what I’ve read so far on beemers in that they are fairly easy to work on will go and go if taken care of, and the communities seem similar in who they attract. Looking forward to learning all I can and the adventures to come.

Chapster out

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