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Top End Rebuild Question


MASSRTRider

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I've decided to undertake doing my own rebuild of the right side cylinder. It has a burnt exhaust valve and I am trying to remove the head to confirm no other damage besides valves. Anyway, in my repair manual it says to use BMW Tool # 11-2-650, the TDC locking pin. Do I need to get this tool or is there another method that can be used? Maybe a screwdriver fits in the same way? It mentions the tool "locks" in place so I suspect I do need this but before I go searching for it I figured I'd see if I really need it. Another question is, am I foolish to be attempting this? I have fairly good mechanical skills but have never done any internal repairs to an engine other than rebuilding top ends on 2 stroke dirt bikes. Those were very simple procedures and if I screwed up the consequences were minor. I'm nervous about ruining the engine though I guess since its not running anyway how much more damage could I really do? Thanks for any advise/answers/tricks.

 

Chuck

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ShovelStrokeEd

The tool is not really essential.

You'll be pulling the cam chain off the right camshaft so that will have to be timed again on assembly. So long as the head is off, you could mount a degree wheel on the front crank pulley and use a simple piston stop to find TDC. You can find the procedure for doing so usually printed right on the degree wheel or do a Google search. Once you have the pointer set, it is a simple matter to verify that the cam is in the correct position. Do be sure that the other cylinder is at TDC overlap or your engine will make some expensive noises.

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Thanks for the replies. Sounds like I will just do the disassembly and then take it to the shop to get it put back together properly. It will be money well spent to make sure its right before I munch something else.

On a side note, I keep forgetting to ask what causes exhaust valves to burn up. I had gone over my usually 6k miles between adjustments, was this a likely cause or a freak occurance? I've gone over 1k past service intervals in the past but the bike was much younger then. Do I need to make sure I do the service before/at 6k? I'm up to almost 80k miles on the bike. This was the only major unplanned work on the bike. All the other major work done has been before failures/problems started. I'm planning on keeping the bike for many more years as the new models just don't do anything for me visually. Now if I could put my bodywork on the new RT that would be something. Thanks again for all your help.

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As flyboy says, too tight exhaust valve clearance can result in burnt exhaust valve. Evidently (I'm not a major wrench) the exhaust valve loses heat by its contact with the surrounding metal (valve seat); when clearance is too tight, valve's brief moments of touching seat decreases with subsequent decrease in opportunity to lose heat.

Now, MASSRTrider, you leave me with a mystery, that is, you say that in your bike's youth you mite go 1000 miles beyond the 6000 mile valve check yet you imply that more recently, you've gone further beyond the 6000 miles, so, how much further ? Was it 10,000 miles, 15,000 miles ? A curious mind wants to know.

 

Wooster, morphing into another MASSRTrider(to avoid copywrite infringement, I'll be MARTrider)

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I keep forgetting to ask what causes exhaust valves to burn up.
Or, it could be the lack of sodium filled stems, combined with bad metallurgy on some production runs. Or, the boxer's propensity to carbon deposits which may stick in the valve seat. Your problem is more common than I'd like to see. Can't remember the last time I heard about a valve burn on a stocker Japanese bike. There have been half a dozen or so reported on 1150's on this DB in the last year or two, all relatively new bikes. DAMHIKT
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David McClain

I've recently pulled the heads off my 95RS and didn't have the factory tool either. After getting the cylinder on TDC I used a 6mm allen wrench to lock the flywheel in place.

Having a Clymer manual also helped out a lot. You know what they say, a picture is worth a thousand words.

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Joe Frickin' Friday

Have had the heads off of my '99 RT a couple of times. Kept engine at TDC by standing on rear brake (geargox in top gear) while torquing the cam sprocket bolts off/on. May also be aided by having someone (brakeman?) sitting on pillion to give the rear wheel some traction, helping to prevent it turning while you're torquing on the aforementioned bolt.

 

Having the engine exactly at TDC for head removal is not critical. The cam sprocket is keyed on the camshaft (though the key is somewhat delicate), so alignment during reinstallation will be obvious, provided you've zip-tied the cam chain in place on the sprocket before removing said sprocket from camshaft.

 

Since you're only pulling one head, just make sure that head is on TDC-compression (i.e. all four valves for that head are closed) when you start. Note that during reinstallation, the camshaft has considerable freedom of rotational movement (not true when at TDC gas-exchange), allowing you to align it properly with the cam sprocket. thumbsup.gif

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ShovelStrokeEd

I find it difficult to credit the too little valve clearance theory. Unless you really screwed up so that the valve was off the seat on the base circle of the cam that is. Going from 0.012" to 0.008" is just not going to change the time that much. Probably not as much as the difference between running the motor at 4000 RPM vs 6000 RPM.

 

I believe carbon is the most common culprit. The real culprit is probably the combustion chamber design. Remember this is a way oversquare motor so there is a huge surface area when you count the piston top and chamber surface. If the swirl pattern in the chamber is not right and there is not enough squish area, carbon buildup is a given and with it will come flecks and chunks getting loose with nowhere to land but the valve seat.

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Now, MASSRTrider, you leave me with a mystery, that is, you say that in your bike's youth you mite go 1000 miles beyond the 6000 mile valve check yet you imply that more recently, you've gone further beyond the 6000 miles, so, how much further ? Was it 10,000 miles, 15,000 miles ? A curious mind wants to know.

 

Wooster, morphing into another MASSRTrider(to avoid copywrite infringement, I'll be MARTrider)

 

Welcome to MA, Sorry I can't resist are you moving to Worcester? It's sometimes pronounced Wooster.

 

Anyway. In answer to you mileage question, while my odometer was at 78915 at the time of failure I looked back through my maintenance records and I had gone in late for the last service and had only gone 5800 miles from last adjustment. I'm not sure if it has any bearing on the problem but when I first got it back from the 73k service I almost took it back because I was having a stalling problem. It was unusually hot for about 2 weeks around here when it was serviced and for about a week the bike started roughly and frequently stalled at stop signs and red lights. I called the shop to bring it back and the next day it started running better and I never did take it back. The weather cooled down about the same time the bike started doing better so I thought it was somehow weather related, though in hindsight it doesn't make much sense to blame the weather. I've ridden in everything from 17 to 105 and other than starting the ambient temperature should not effect the operation of the engine.

 

As to Ed's comment about carbon build up. I've always heard that if you run an engine fairly hard that should keep carbon deposits to a minimum. Well I'm probably the poster child for running it hard. I typically cruise in the 3.5k to 6k RPM range. I always thought that these engines were built for performance and could therefore handle the high RPM's. Have I been pushing it a little to hard and do high RPM's really help ward off carbon build up? Finally once I get the head to a shop and have it torn down should the rebuilder be able to tell me the cause of failure or will it always be a guess?

 

Mitch I like your idea of the brakeman.

 

Thanks again for all the help.

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Ed, what precautions can you take to help eliminate the carbon build up and flaking problem? Higher revs, tectron treatments regularily, etc? I think I read were Mitch was having a pinging/carbon build up problem and he just put in ear plugs and rode it harder (higher revs regularily)!! I beleive it went away or was less of a problem?? Just curious, my RT runs great at 18,000 miles(and I have done the 6000 mile valve adjustments, throtle syncs, and fluid changes) but want to keep carbon and possible burnt valve at bay!!

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I've been trying to buy a used head and do the repairs myself. I have been amazed at the condition of the combustion chambers compared to mine. I've seen heads from an engine with 51k miles and another with 40k something miles and they looked awful. Heavy black build up and discolored exhaust valves. My engine has 79k and the head is dark brown and tan. One thing I've noticed in all three is that one exhaust valve is typically discolored. It appears that it may bear the brunt of the gases escaping and the other valve is just along for the ride. I'm now wondering if I should just replace the valve in my head. The condition of the used parts seems like I'll just be inviting more trouble down the road. In my mind I think running high RPM's is a good thing for the engine. I know they are designed to be performance oriented and in theory should be able to handle the stress. Based on the people who have seen the damaged valve the consensus is a defect in the valve that has been present since new. A bad casting/hairline crack or something of that nature. There is a 3/8" hole near the edge of the valve and there was no colateral damage to the plug/head/cylinder wall. I now am going to take the head into a shop and see what they think about just replacing the one failed valve and related pieces. I don't want to spend huge money on the bike at this time just want to get it back to ridable. Any thoughts as to wether or not this is a good idea? Thanks.

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