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Thread: 1978 R100/7 Topend Overhaul

  1. #61
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    Quote Originally Posted by 140008 View Post
    Why not just put some new rings in and break them in.
    I'm not sure the bike was running that "fine". I was getting pinging once in a while and have a few scares with valves closing up...or at least I thought they might have been. And there has always been this concern in the back of my mind about running on the original valves and seats...I had the feeling that it was a time bomb. I'd rather not have that in the back of my mind...I want to enjoy riding.

    I think there is enough wear that the piston is going to be sloppy in the bore and even if I could go to some new rings, it just wouldn't be as tight as it should be. I'd be back to that worry mode.

    I went up to BMW today to price cylinders, pistons, and wrist pins. Without even trying to match up the right size parts, I was well north of $2500. So, I'll be calling Ted next week and ordering a kit from him to finish this out. Matching parts and lighter...I'll certainly have less to worry about.
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  2. #62
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    FWIW, when it comes to spending a little cash on a bike that's been down the road with yerself, like a friend, it's cash we'll spent. Can't take the cash with'ya. Measure the old pistons and cylinders, put'em in the flea market. Yes, an old airhead can be had for a few grand, but a sweet running airhead needs a little cash and TLC every few years. Which yields big smiles. All looks super nice so far, good job.

  3. #63
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    Did some cleaning today. Also removed the cam followers to see what the surfaces looked like. The left were pristine, but the right have some small pits. Any thoughts on reusing them? I'll have to think about this.
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    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  4. #64
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    I also made some measurements for reference.

    The head bolts measured between 252 to 254mm from the case surface to the end of the head bolt. This is pretty much standard...these head bolts were installed at the factory and have never been messed with AFAIK.

    I also measured the ring end gaps, for kicks, even though I'm going to change everything. Just wanted to see where I was running. I made the measurements with the ring squared in the bore by the piston at about half stroke. The rings are listed from the top of the piston to the bottom of the piston.

    Left: - Top (or outer) ring -- 0.52mm (spec is 0.50))
    - Middle -- 0.35mm (spec is 0.45)
    - Oil ring (first of three piece oil ring) -- 1.29mm (spec is 0.40)
    - Oil ring (second of the three) -- 1.13mm (same spec)

    Right:
    - Top -- 0.38mm
    - Middle -- 0.48mm
    - Oil ring (first of three piece oil ring) -- 1.37mm
    - Oil ring (second of the three) -- 1.21mm

    The oil ring gaps were HUGE...it's a wonder I wasn't pumping oil through the engine.
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  5. #65
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    Why replace cylinders?

    Why are you considering replacing cylinders?

    If you are going to replace pistons, and rings, why not purchase oversize pistons and rings and then bore the old cylinders to match?

    Isn't that how it is usually done?

  6. #66
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    Quote Originally Posted by jimmylee View Post
    Why are you considering replacing cylinders?

    If you are going to replace pistons, and rings, why not purchase oversize pistons and rings and then bore the old cylinders to match?

    Isn't that how it is usually done?
    Because the wisdom, as I've heard it, that bored out 1000cc jugs aren't stable and likely will cause troubles later on. New BMW pistons run something like $900 after checking this weekend. So, I can spend +$1000 boring my current cylinders and getting new pistons and rings and have a potential problem facing in the future. Or I can spend the same amount of money and get all new stuff with lighter pistons and wrist pins and feel better about a longer future. That's they way I'm going to go.
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  7. #67
    #4869 DennisDarrow's Avatar
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    Looks like it was totally time, from the end gaps to do exactly what you are doing! Yes, surprised you had the compression you had as well as not a lot of oil consumption. Anyway, NOW you know mostly everything you need to know.....OR........Did you ever plastiguage your rod bearings?..........Just another step but it sure lets you know about your bottom end.
    Does one have to purchase lifters by the set?....If not the left's surely look good to me. Glad you are making the progress that you are and following a LOGICAL replacement standard rather than just following what your money can buy.........God bless.......Dennis

  8. #68
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    Dennis -

    No, I have not done the plastigage measurement. I actually meant to try and get feeler gages in there or, at a minimum, see if I could feel any in-out movement of the rod. Actually, it seems a bit difficult to get anything inside that 99mm hole in the case with the rod sticking through the middle! I'll have to give another look.
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  9. #69
    Monza Blue 1974 R90/6
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    Kurt,

    I found the same problem with my lifters last year this time when I did a pushrod seal replacement.

    I can't find my old posts using the "search" function, but if there is a trick and you can find it, you will see the pictures I posted and the feedback/opinions that were offered.

    I ended up replacing the ones that had any evidence of pits. It was an unexpected expense. Primary feedback I got was that surface was hardened and once the pitting started, wear would be more rapid.

    I don't envy you on the decision about the cylinders. But, what is downside to new rings and a hone and see how it works with the new valves? I haven't priced the rings, but would the cost of gaskets, rings, and the hone be worth a try? You might get a couple more years out of it which will give you plenty of time to decide if you want to invest in new cylinders and pistons.

    Barron

  10. #70
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    Quote Originally Posted by Barron_Williams View Post
    But, what is downside to new rings and a hone and see how it works with the new valves? I haven't priced the rings, but would the cost of gaskets, rings, and the hone be worth a try?
    But have you priced pistons? They're quite a shock from BMW, nearly the cost of the other replacement kit. I think because of the wear I have, being tapered and out of round, just new rings won't seal very well. Plus the piston will have too much clearance and will rock in the bore over time. So, I see the only option is going first over with all new parts...very expensive and can be troublesome down the road. I don't want that...I want to bolt on something that will work for me for the next 50K+ miles without having to worry if things are OK or not.
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  11. #71
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    Good Job

    You've made the right call here, Kurt. I'm no expert, but I do know how to read and understand what the sages say, and just about ALL of them say DO NOT TRY TO OVERBORE the liter bikes. Besides, as you've correctly noted, the "savings" even in just dollars is not significant when you buy new, versus taking a chance on "mixing and matching." If the re-bore goes sideways, oh, brother!

    Even some respected cylinder shops will tell you that you CAN do this, so buyer beware, IMHO. I'm guessing that the overbore would work fine for awhile, and would offer improved performance for awhile. After awhile, not so sure. For those of us expecting to put high mileage on a rebuilt engine, and who don't appreciate strange sounds coming from "down there" while in the middle of the Mojave. . .that expensive man-jewelry is worth every dime.

    I've now done two of these "Siebenrock replacements" and am about to do a third, all on different '78 R100RS's. Before doing the first one, I went through the same due diligence that you've shared on this thread. You will NOT be sorry that you went this route, but that's just my .02.

    Walking Eagle

  12. #72
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    Thanks Walking Eagle...those are my sentiments. Also good to know that there's at least one satisfied customer out there!! The kit should be arriving later next week.
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  13. #73
    Cave Creek AZ 85K100LT's Avatar
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    Unhappy Lifters pitting

    Yes once pitting starts on those lifters it will progress. looks like you have 2 to replace the other 2 look good.

    I can see with the head work and new cylinders you will have spent $2K+ it is expensive. I spent over 2k getting the heads done BMW valves, rings replaced on my 89 GS - now you have to keep it get you money's worth. My 89 GS runs great now. Money well spent ( well not in the wife's view)

    You will be happy!!!
    1974 R75/6 W Sidecar
    1989 R100GS


  14. #74
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    Lifters will be replaced....I can't go down the road wondering. I will replace all four...keep the other two "good" ones as spares.
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  15. #75
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    Bought some new cam followers...ouch, those puppies are expensive! I guess they're pretty critical, huh!!

    I was a little shocked to see what they looked like new. A bit gnarly if you ask me...seeming a bit grungy, rough. I understand that I'm supposed to clean them up, maybe with some brake cleaner. Here's a comparison of the old (left) and new (right).

    Since the reassembly won't happen overnight, I suspect that I'll need more than just a coating of oil on the parts. Anyone have suggestions on some type of assembly lube so that the parts are well lubed when I do start it for the first time?
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    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

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