New to the forum/site. I've been slowly restoring a basketcase 1958 R69 for the past 15 years, and have a question about a company I came across Cyclewareables
which sells 72mm cylinder sleeves, requiring you to bore out the cylinder to fit them in. Has anyone done this? I've heard Volkswagon has done this for years, or used to. Is this too good to be true/bad idea? TIA
I have never had a cylinder sleeved myself, but I've heard that it can be successful. However, I've also heard that if the sleeving isn't done right, it can lead to hot spots in the cylinder and seizing. And of course, boring a cylinder to accept a sleeve means that it's too big to accept any normal oversize piston. I was able to have the cylinders on my R51/3 bored to 3rd over and it runs very well; there are 4th over pistons available for it, so I'm not currently considering sleeving as an option.
How far out are your cylinders right now? Do you need to go to a sleeve at this point?
This may be way off the mark, but I had one of the cylinders on my '59 Mercedes sleeved 25 years ago and I am still driving it. More to the point, vintage BMW cylinders, pistons, and heads show up fairly frequently on ebay. Why not start with one that is on the original or first or second overbore?
I would think that experience sleeving a low revving water cooled motor might not transfer perfectly to a high revving, cast iron, air cooled motor. As I understand it, the problem with sleeving is getting the sleeve installed so that is always in perfect contact with the cylinder. If the rates of expansion of the sleeve and the cylinder are not compatible throughout the operating temperature range, it's a recipe for trouble.
Since your 4th over is still working for you, use the time to find a good set of replacement cylinders. You may never need to do anything with your current cylinders, depending on how much you end up riding the bike, but if you can acquire a good set, you'll never have to worry about it. And you (or someone you sell them to) can still sleeve the old cylinders after replacing them.
That's my 2c. Good luck, whatever approach you take.
Just curious, is there enough material left in the original cylinders to bore once more and install sleeves? I've never heard of 4th over being a viable solution for long term running. 3rd over is about as far as people go. Too much farther and some of the embedded support structure of the cylinder begins to influence the ovality of the cylinder...bringing the hot spots, etc., that Darryl mentioned into the picture.
I have a 1952 R67/2 where the sleeves were not done correctly, and as mentioned above by Darryl, one of the pistons grew hot and began to seize (ran really,really hot and had smoke coming from the area). When I took the cylinder(s) to a mechanic who specialized in this type of work he said the prior sleeve job was not done correctly as it was missing a coat of silicon between the sleeve and the cylinder. This guy pushed the old sleeves out, bored the cylinders, re-did the sleeve job (both cylinders) and some paint work for around $450 (I had this done within the last 12 months).
Of course the piston on that side was ruined by the seizing. So with the boring/resleeving/bad piston - I had to get two new pistons from Vech for around $480. Total cost to fix problem around $1,000. No problems since.
I talked to Vech as I went throught the process - it is fairly common on these bikes and if done right will hold up forever. I did not use the company you reference but someone local to me in Florida. I hope this helps from first-hand experience.
The old bike runs like a champ once again!
Due a deep rust scar, the cylinder of my basket case R27 was rebored to 4th oversize in 1998.
Piston, 70.0mm (+2.0mm) 11 25 0 012 131.2
The engine broke in perfectly, and has run very strongly for the past 9,000 miles. There is no measurable oil consumption, and the oil is so clean at 500 miles that I usually let it go to 1,000 miles between changes.
I don't see that Darryl said anything against 4th oversize for pistons; his comment seemed to be about the even more amount of material removed for sleeving.
Stock size would be around 72mm, so 72.9mm would be 2nd oversize...one oversize should be 0.5mm.
OK, so why are you considering doing this again? Seems to me that you need to go through a thorough measurement process on the cylinders for diameter and ovality at the top, middle, and bottom of the range. Measure the pistons. Measure the piston to cylinder gap. Measure the ring gaps. All is is prescribed processes.
Then with that information decide what's next. Maybe you're OK where you're at...maybe you just need a set of rings. I believe the early motors came with the 5-ring set. If you end up buying new pistons, most likely it will be the 3-ring variety. If you end up reboring, you should get good input from a machinist and get all the parts together. Bore-Tech is a company that can bore to match whatever pistons you buy and they can also apply a carbide coating to the cylinder walls. Check out their website.
Regarding reboring, it's been mentioned that going too many sizes over can be problematic. Duane Ausherman discusses that on his website:
Just below the picture of the piston with ring orientation, he discusses his experience with going 3rd and 4th over.
Duane only says "My experience with the 3rd and 4th over pistons wasn't good and I quit boring them out that far." It appears that certain pistons were the problem, not the principle of overboring itself.
You said "3rd over is about as far as people go. Too much farther... bringing the hot spots, etc., that Darryl mentioned into the picture." But Darryl was talking about sleeving, not overboring.
The 4th oversize Huggett piston has worked well in my R27 for 13 years and 9,000 miles. Overboring to 3rd or 4th size seems like a viable option if one cannot find or afford more cylinders.
So the general opinions then are that sleeving may be problematic and that certain pistons might also create a problem when going too large. Meaning that getting the best possible service and parts is critical. As one might expect with any work of this nature.
If it were me, I'd want to ask about how far one can reasonably go with any kind of over bore situation, whether sleeving or just putting in larger pistons. The R27 and R69 might be different in that respect. Just how far dimensionally can the cylinder be taken without creating a problem? Probably wouldn't hurt to check with some experts on the R69, someone who has done the job. Give Vech a call...he'll let you know what your options are. Or with Bore-Tech. Bob's BMW works on these bikes, but they probably really just send things out anyway...not really sure on that, though.
My R25/3 was too far gone to overbore, so Bore Tech resleeved it and went back to a standard piston It has been running fine since. My suggestion is to send your pistons along with the cylinders, so Bill can fit them properly.