Piston top missing !?

[thessler]

Hi
I just joined this forum and have a few questions about the bike I just picked up. Maybe I could get some advice.

I have an 84 previous told me it is a 650 so I am taking a leap of faith and figure it must be a R 65.

Previous owner replaced the valve seats, I don't know why. He put it together and rode 40 miles and a valve head snaped off and destroyed the head and the entire top of the piston is just gone.

So I figure to start I have to track down the rest of the piston.
I'm guessing it is in the crank case in little pieces.

My question would be has anyone experienced this and have a method for flushing out the crank case ?
Why would a valve just snap off?

 As of now I have no manual, I am still in the thinking and planing stage.
  Thanks for any advice,  Tom

[montmil]

Tom, you have arrived at the Temple of R65 Wisdom. Welcome to our happy asylum.

Hope you got a really good deal on the bike. I'd bet it's an exhaust valve that dropped in unannounced. "Why would a valve just snap off?" We'll save that question for later.

Before you get too far into the repairs, BUY A MANUAL! Both Haynes and Clymer, if you can afford them. Wait... you just bought a bargain BMW. Sure, you can afford 'em!

You can remove the oil sump/pan on an Airhead quite easily. You will likely find enough bits of the piston to create a nice rattle in a soup can. Buy a fresh gasket for later. No goop-sticky stuff-form a cruddy gasket short cuts allowed.

Visit the FAQs section and grab the R65 owners manual in pdf format. Start reading while you shop for the manuals. Check the head stock for the VIN number and post that plus a photo of your scooter. We can tell you what cha got.

Not too worry, we'll get you up and running in just a little while. Besides seeing photos of member's bikes, we love spending your money.

Let us know something...

Monte

  

[Barry]

My question would be has anyone experienced this and have a method for flushing out the crank case ?
Why would a valve just snap off?

Welcome Tom,

The original valves are two piece with a welded joint and it's not unheard of for the head to snap off at the joint usually after a substantial mileage. Why did it do that just after the new seats were fitted ? maybe the valves already had a high mileage on them and were not replaced or more likely something was done wrong like the seat came loose and that caused the valve to fail. Don't know who did the seat job but there is a strong belief that head work should only be entrusted to the few shops experienced with these heads.

Could also be a combination of things including overheating of the valve for some reason. One odd possibility is grossly excessive valve clearances which were so wide that they bypassed the slow ramp phase of the cam which means when the valve is closed it drops abruptly onto the seat rather than being eased down gently by the closing ramp. A combination of overheating and the excessive shock could break the head off.

As you are in the planning stage it might be worth investigating a replacement engine from a breaker. Besides the valve, piston and head the barrel could be damaged and even the conrod bent.

[tvrla]

Should you decide to rebuild the motor, be sure the head you replace has the larger 36 and 40mm valves. The early (pre 1980) R65s have smaller valves.

I've seen cylinders and pistons for these bikes fairly regularly and resonably priced. If there was enough force to remove the piston top, I'd definitely inspect the rod!

When cleaning, don't forget the oil galleys! Remove the screwed-in plugs and pressure sender unit and flush, flush, flush! The janitorial duties on this one will be the killer.

[thessler]

Thanks for the replys

I just ordered a head from E Bay, not knowing they could have different valve sizes. I guess that was a little premature.

 Is there a listing with part numbers to see what year head I am getting ?
I checked the site on the FAQ put in the 7 digit number and came up empty.

Two people mentioned checking the conrod to see if it is bent, that scares me.
Is there anyway to see if it is bent while it's still in the motor ?

I really don't want to dismantle the motor just to put the rod on the bench and see if it looks straight.

 In fact I was hoping this would be an easy fix , new head new piston a thourough cleaning and away we go !!
 Thanks for any advice,  Tom

[Barry]

Is there anyway to see if it is bent while it's still in the motor ?

I really don't want to dismantle the motor just to put the rod on the bench and see if it looks straight.
 

If it was grossly bent you would see it in situ but the proper way is to accurately check the big end axis and small end axis are still parallel by inserting bars through the bearings. Here's a picture of a con-rod being measured.

As an approximate check you could leave it in situ and use one bar through the small end to check it's parallel with the crankcase cylinder joint face.

http://www.flickr.com/photos/74168320@N00/3424646984/#/
(Queer looking split con-rod but you get the idea)

[tvrla]

It's actually not difficult to remove the rod. It does take a special tool to remove the two rod bolts, but that's a common VW item and available at most of the larger auto supplys.

If you watch, it's also possible to find R65 parts fairly cheaply. You want to do this right - and if the rod is bent you'll definitely want it straightened or replaced with one that is. That's part of being a mechanic - inspecting parts for wear or damage, then repair or replace. Sometimes it turns out to be more than expected, and other times less. But you don't want to get it all together then wonder if that odd sound is because the rod is bent. You'll know it isn't because you checked it!

Hope you didn't just buy that set of small valve heads off ebay - I asked him what they were, but don't think he put that data in the listing - possibly hoping to snag a buyer who didn't know there was a difference.

[thessler]

Hi
 I took a look at that rod pretty carefully, it looks good to the naked eye. I may or may not pull it out, not sure.

Wirespokes- yes that sounds like the heads I just bought, and it sounds like he snaged somone who didn't know they have small valves.
Not off to such a good start  

Would it matter if I installed the heads with the smaller valves ?
I'm sure there would be some power loss.  I can live with that.

I am going to need a new piston.
 Is there a way to tell if the one that is wrecked is original and not over sized ? There are some markings on the skirt but nothing that makes any sense to me.
  Thanks for the Help,  Tom

[Dave 2]

Is there a listing with part numbers to see what year head I am getting ?

These are two sites that I find very helpful for identifying and pricing parts http://www.realoem.com/bmw and http://www.maxbmwmotorcycles.com/fiche/fiche.asp good luck! D2

[Barry]

Pistons are graded A B C

A   81.955 - 81.965
 
B   81.965 - 81.975

C   81.975 - 81.985

There was a recent thread that discussed small valve heads vs big valve heads. I doubt you'd notice much power loss. The small valve head is 5 HP down at the same maximum revs of 7250 RPM and peak torque is down by 1.7 lbft but that's at the 5500 RPM instead of 6500 RPM which fits the normal scheme of things. A small valve head should be better in the low to mid range and a big valve head better at top end. It's got to be vastly more important that both are the same.

[thessler]

Thanks barry

I am getting both heads so as long as I can use them both thats good enough.
 
Piston info is good now I have a starting place.
 Thanks, Tom

[Barry]

Just checking the original riders handbooks there's not a huge difference in claimed performance:-

0 - 62 MPH  5.8 Sec   vs  5.9 Sec

0 - 400m    14.3 Sec  vs  14.7 Sec

0 - 1000m  28.1 Sec  vs  28.5 Sec

My R45 is a little further behind at 7.4, 15.8 and 30.7


The torque graphs show that 45HP and 50HP R65's make the same amount of torque at 5500RPM but on the more powerful engine it continues to rise a little up to 6500RPM while on the other it starts to fall away.

[tvrla]

You really need a caliper or bore gauge to know what you've got. Or, most likely (and this is an assumption) both sides are the same - in which case, when you pull the other side head, clean off the piston and read the numbers on the crown. Try the other cylinder on that good piston and see how it fits. That will tell you something right there.

As for the heads, sure, you can run them as is. I'm not sure if there are any other differences than the valves, but you could compare for yourself. Not sure if you'd be able to notice any differences in the intake or exhaust tracts. If the casting numbers are the same, all you'd have to do is have a shop install larger valves. But a better solution would be to send off the damaged head and have it repaired while you're riding with the small valves.

Install the wrist pin into the rod and take some very careful measurements from the pin to the outside edge of the case. Make sure it's the same distance front and back. Another way would be to install the piston with pin, and rotate the crankshaft till the piston almost touches the block. Have a straight edge (or something straight and even) lying across the top studs and see if both sides of the piston contact evenly.

[thessler]

Ok thanks for the replys

I will pull the other head and see if the other piston crown is marked.

As far as my old head is concerned I doubt anybody can fix it, there is a tremendous amount of damage.
Good tips on checking the rod. If those measurements check out that i'll go with it.

 Any good sources for aftermarket parts ??

   Thanks, Tom  

[tvrla]

You're welcome!

BMW piston tops always have the size stamped in the top. And since you're going to be in there anyway, take a look now and start cleaning up the piston and head. Also, you'll want to compare a prospective new piston to your current good one - make absolutely certain they're matched - both the same dome shape. I'm not sure if there were different compression ratios during the 650 production run, so that's something to check out.

Go to the ibmwr site and find the link for wrecking yards or parts or whatever. There are really quite a few, and a good used piston (maybe even with it's mating barell) could cost $50. Maybe half that.