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Old 01-24-2013, 11:49 PM   #16
Umarth OP
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Quote:
Originally Posted by gunnerbuck View Post
You could also install a thicker base gasket to slightly lower the compression, this would smooth things out a bit and make the engine less high strung.... I picked up four base gaskets that are intended for the early model LC 4 and are 0.7 thick compared to the 0.5 of the later bikes...

With the stock exhaust just pull the disk pack off the back of the muffler and then drill a bunch of small holes in the end plate {swiss cheese effect} around the core pipe... These holes will create a shortcut past the restriction and let some of the exhaust through without much increase in noise... When you reassemble add another 3 or 4 disks to the stack...
Oh I like that idea of simply reducing the compression ratio! Brilliant!
The thicker ones, where from what year model?

as for the exhaust mods, I'm pretty sure I don't follow your instructions but that's simply because I've never taken one apart, so I'm not visualizing the steps. Google time! :)

thanks for the info!
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Old 01-25-2013, 02:47 AM   #17
achile
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Originally Posted by Umarth View Post
It all started when I went to do a routine oil change on my 640 adv with 40,000 km.
Noticed the oil was like milk chocolate.
No big deal: had all the parts for water pump rebuild in hand.

So I fixed the water pump. In doing so, looked at the piston and figured,bah while I'm here might as well clean it too and check what the cylinder walls look like and check the ring gaps. So proceeded and remove the cylinder.

Now I'm thinking, since I have 3 and 1/2 months left before the big ass trip (100,000 km estimated), maybee I should crack open the case and check out the wear on the trans an replace some bearing in there while I'm at it.

My question is, any reason I should refrain from doing it? I'm learning all this shit as I go along, beeing a noob mechanic after all. But I'm not affraid to get my hands dirty and, more importantly, the more I know this bikes internals the better prepared I'll be when it craps out in the middle of patagonia or the sahara.

And If I do go and crack the case, what should I be looking for exactly and what parts would be good candidates for preemptive replacement? Main bearing? all the bearings? the gears? I dont want to spend uselessly on this (takes away from travel money - beer) but, well, you know...
My friend, it seems to mee that you have an all-mighty itch to crack it open and see how it ticks. So...you are seeking the approuval of your peers...

DO IT! Change the worn parts and you'll sleep better in Patagonia.
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Old 01-25-2013, 03:42 AM   #18
mountaincadre
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Well if your doing Europe you might as well pop in or a cup ae cha(tea), i'm in Scotland, the weathers shite but the roads are braw.Hey gunner i've taken your advice and dicided not to fit the 660 rallye cam to mine as it's already nippy enough and like you said "the more you tune it the greater the chance of self destruction and the more i'll have to service it", i'm half way through the rebuild of mine, i;ll post some picks when it's finished.
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Old 01-25-2013, 04:08 AM   #19
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Originally Posted by mountaincadre View Post
Well if your doing Europe you might as well pop in or a cup ae cha(tea), i'm in Scotland, the weathers shite but the roads are braw.Hey gunner i've taken your advice and dicided not to fit the 660 rallye cam to mine as it's already nippy enough and like you said "the more you tune it the greater the chance of self destruction and the more i'll have to service it", i'm half way through the rebuild of mine, i;ll post some picks when it's finished.
I did my top end last november. I had a difficult choice to make. Go stock or put in hotcams and big bore. I went with the stockye. It all depends on what you want to do with it and how it reflects on your finances. Are 4-8 hp worth spending a few houndred bucks and increasing the risk of a fatal engine faliure?(maybe at high speed, with you on it?) Service costs? I'd rather have it in perfect shape and stock. (I'm talking about the BRP I own since 2008.)
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Old 01-25-2013, 04:54 AM   #20
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Originally Posted by achile View Post
I did my top end last november. I had a difficult choice to make. Go stock or put in hotcams and big bore. I went with the stockye. It all depends on what you want to do with it and how it reflects on your finances. Are 4-8 hp worth spending a few houndred bucks and increasing the risk of a fatal engine faliure?(maybe at high speed, with you on it?) Service costs? I'd rather have it in perfect shape and stock. (I'm talking about the BRP I own since 2008.)
Aye Achile that's the conclusion i've come to, mine has 54 at the rear wheel and that feels more than enough.
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Old 01-25-2013, 09:02 AM   #21
gunnerbuck
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Cylinder


The scratches that show for the most part are pretty minor... The deeper scratch is pretty narrow likely will not have much effect.. But then again you are going on a long journey, the top end is apart, so now would be the time for a complete refresh if you have the funds... The scratching is likely caused by hard particles getting past the filter...

The budget fix would be to order a new set of piston rings and have the cylinder honed... You would probably be looking at $100-$120 total to restore to 95%...

To go 100% you'll need to have the cylinder replated or replaced and go with new rings or a new piston... Replating usually costs around $300 and a stock piston $350 VS $180 for a Pro X or $220 for a Wossner... Stock rings are about $60...

Wossner piston are the lightest and there have been some claims that they smooth the engine out, but I have noticed that with a refreshed top end regardless of piston brand, the engine will feel smoother...

The 02 and prior 640s with the low flo head used the thicker base gasket.. The low flow cylinder has larger alignment dowels so this difference in the gaskets will have to be addressed... Some have just installed the gasket filling the dowel gap with sealant while applying it to the cam tunnel area as recommended in the manual... My plan is to sacrifice one of the four gaskets I have and cut out little filler donuts to make up the difference...

One of my 640s has the compression reduced via combustion well milling and it is noticeably smoother than the other which is in stock form... The power between the lowered compression bike VS the stock is hard to compare because the lowered bike has an SM exhaust vs the others oem cored unit...
With the SM pipe the comp reduced bike has less low grunt end but more on top and uses a slight bit more fuel, maybe about 1-2KM less range per liter... These differences may be due to the freer flowing exhaust and nothing else... The only way to tell for sure is to switch exhausts and see how it compares...




f
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Old 01-25-2013, 11:23 AM   #22
rob748
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2 cents

i replaced the piston and had a sleeve put in and put two new valves in and decided not to do the bottom end. its lasted 5000 miles and went boom, it needs new bore, piston rings plus the bottom.
if i did it again i would have refreshed the bottom at the same time.
mine was raced a lot so the miles don't mean a lot
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Old 01-25-2013, 05:18 PM   #23
Umarth OP
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Quote:
Originally Posted by achile View Post
My friend, it seems to mee that you have an all-mighty itch to crack it open and see how it ticks. So...you are seeking the approuval of your peers...

DO IT! Change the worn parts and you'll sleep better in Patagonia.
I do but it's also countered by the "if it ain't broke, don't fix it". Especialy since this would be the first time I ever take a motor completely apart and would be a hands on learning experience. Kind of like learning to drive standard: you do it with someone else's car...

I'll go with gunners recomendation which makes a lot of sense.
But yeah, really would of liked to crack it open!
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Old 01-25-2013, 08:52 PM   #24
bmwktmbill
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[QUOTE=gunnerbuck;20572417]

The 02 and prior 640s with the low flo head used the thicker base gasket.. The low flow cylinder has larger alignment dowels so this difference in the gaskets will have to be addressed... Some have just installed the gasket filling the dowel gap with sealant while applying it to the cam tunnel area as recommended in the manual... My plan is to sacrifice one of the four gaskets I have and cut out little filler donuts to make up the difference..
Quote by Gunnerbuck


Yikes Gunner reading ths I realize that when my piston blew in Panama I used a 'high flow' gasket on my 'low flow' cylinder effectively raising the compression...hmmm well nothing has blown up yet and it has many more miles. I had to drill out the holes for the dowels. I thought that was strange and it pissed me off at the time. I was carrying a base gasket with me fron the local dealer.Come to thinkofitI think I used a pocket knife to enlarge the holes.

The motorcycle surely had more snap after the new piston was in and runs really nicely with reground valves and 17/42 gearing. Mpg is better too.

Oh well.
Another first?
Others?
bill
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bmwktmbill screwed with this post 01-25-2013 at 09:11 PM
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