About 2 years ago I rebuild my engine after buying my xr600 and have the piston grenading on me the first week.. (this topic: http://www.thumperta...2784&highlight= )
Then I rode the bike pretty hard for about 7500km's..noticed no problems. I've put a FCR41MX carb on it but made no other changes.

I had a organised enduro trip today, and halfway the first round, in very heavy sand, my engine started making a tapping sound, and about 500m later, when I stopped and got of the gass it died.. no more compression.

At home I took the topend off and I noticed the 'decompression' exhaust valve had been hitting the piston and leaked! So that's probably why I lost compression.
I don't have a clue how only one exhaust valve can hit the piston.. maybe it got stuck?

I also noticed 3 of 4 lobes of the hotcams camshaft were worn and 3 of 4 rockers were also worn away! The fourth rocker and camshaft lobe (at the end of the camshaft) was in perfect condition!

The rockers do not show any lack of oil or heat discoloring. They look perfect but are just eaten away.. The bearing in the middle of the camshaft is also still perfect.. so it looks like it wasn't an oil problem..

I haven't checked valve clearance for a while... for maybe 1500-2000km's, but I ride it pretty hard. I used to check it often after the rebuild, but clearance didn't change much so I stopped checking after every hard ride. Figured it isn't a CRF....
So maybe valve clearance was too tight or something, which made them chew on each other??
I've been finding a little gray mist in my oil changes since after the rebuild..figured it was normal, but it probably was the rockers already wearing away a little.. but like I said, valve clearance was never far off.

Cilinder and nicasil still in perfect condition thank god!

So I'm completely puzzled at how the right exhaust valve could hit the piston, and how three of four cam lobes&rockers can wear this much with proper lubrication.

Anyone got any ideas? I'll post some pictures tomorrow.

I`ve seen quite a pile of those cams eaten,,,and no reason for it..no way i`d put one in my bike,too risky..

Let`s see some pics of the head,cam and rockers..it`ll help....

Did you use HotCams clearance specs when setting the valves?,,check your downtube sceen for debris..

Did you verify oil flow at initial start-up by cracking the banjo bolt loose on the line going to the head..???

B

brianhare said:

Yes, I always checked for oil flow after oil changes, primed the oil pump by putting compressed air on the oil reservoir to pop open the check valve.

I think I always used the workshop valve specs though... (IN 0.1mm and EX 0.12mm) crap . So that must be the cause..
So I set it up too tight, and didn't check often so probably they got a bit tighter...  The cam has probably started to gall, and then wore through the chromed rocker facing and things started wearing pretty bad.

I just looked up the hotcams install sheet and with it came a little card that indeed notes specs for valve lash: "instake 0.15 -exhaust 0.2" Think I missed that when installing.

(Btw: Just measured the lobe difference between stock and hotcams and theres 1mm more lift with the hotcams shaft.)

As for mrs. valve kissing mr. piston... Just checked camchain wear by trying to lift it from the camshaft sprocket, and it was very loose. Also, my chain tensioner looks damaged on the inside of the roller construction, little pieces of plastic missing..
I do have a manual tensioning bolt installed, but I really suspect it skipped a tooth.

So why did only 1 valve hit the piston? The camshaft wear made the other one close sooner...

The rockers were the cheap set of ebay by the way. Something like 50$ for all 4 of them. OEM they are 50$ a piece around here!
Here's some pics:







I'll try to get a used head with oem rockers and camshaft so I can enjoy the rest of the enduro season. We hired a mx track with some people for the 18th of November so I would like to have it running at that date. Maybe I'll buy a new Hotcams camshaft later.
I'll also order a new camchaintensioner and camchain. Hopefully no more problems after that.

I think the e-bay rockers is what caused your cam wear, I had the same problem on my boys XR250 when I bought the e-bay rockers.
Now what I do is have them hard welded because there cheap enough to purchase.

pwrpapa said:

I see.. Well, one of them rockers is still in good shape.. so I don't know for shure.

Do you hard weld them and use them with a normal camshaft? I always thought you needed a hard welded camshaft also for that.

pwrpapa said:

Agree. The hard face, if any, wears off the cheap rocker contact surfaces causing them to gall and eat up the cam lobes.

I'm going to say the damage was done right after the re-build, may have had a lack of oil just long enough to start the wear. I say this because I had the same thing happen to me. i bought a rocker box off ebay with stock rockers in it and used them. I also because the cam doesn't line up perfectly with the rockers, as you can see in your pics i also polished my cam, it gave me a mirror finish on the lobes and broke the edge just enough for them to not be sharp, have about 1200 miles so far and all looks like new.
Moral being, after rebuild and prime, break banjo bolt at head loose and watch for oil at start up, you get oil-good to go, no oil after 5-10 seconds,shut it down.
Oil change I put one quart in rocker cap on the rear right side, one in the frame, then I know oil is there and it drains to the sump quicker

thumpharder said:

I must say I checked with a light into the valve cap hole a couple of times after rebuild, and it looked like everything was fine..
Also put oil in de head on first startup.

I changed the oil every 1500-2000km's and found a light mist of particles in it. Thought it was normal from the hard offroad use... I think it was the cam and rockers..
After oil changes I always checked if there was oil flow. I didn't pour oil in the oil cap after oil changes though.. but I'm shure it wasnt an oil problem as the middle bearing is perfect, and the fourth cam lobe&rocker also!

Probably was a combination of cheap ebay-rockers and oem valve specs instead of hotcams specs.

Been trying to get a new set of used rockers and used camshaft but people want like 300$ for them!! I mean those parts are used and 20yrs old!  I'll buy a new hotcams camshaft.. too bad I'll probably wil receive it in 3-4 weeks when riding season (organised enduro's) is almost over again..

Well... I had to get the bike finished for today (track day).. Did a valve job (recut the seats), replaced valves, replaced camchain and camchain tensioner.. the old chain was stretched pretty badly! I could get the old chain of the camshaft sprocket without undoing the camsprocket bolts... new chain was very thight even without the tensioner. Worked until 00.30 in the night to get it finished, and did the hot cams break-in procedure this morning.
I think I found some of it's power back. After the break-in procedure (30min drive above 3000rpm and checking valve-clearances) I loaded up the bike and drove it on the track. It was a f* awesome day I must say...I don't drive on the track often and it's like going to disney land when I was a kid! (although actually, I've never been there)
I also changed the old 88-90 shock to a newer xr600 98 shock... wow what a difference!
I'll check valve clearances again tomorrow... hope she lasts a while this time!

Edited by Ilja, 19 November 2011 - 04:19 AM.

Ilja said:

For that kind of money if would be more worthwhile to spend a bit more and get a hardwelded MegaCycle or Web cam and rockers.

I have been burned and seen others get burned enough times to not consider buying CCC (cheap Chinese crap) versions of anything important like engine parts.

Something else I personally think gives the Hot Cam a better chance at life is to install it with a high quality camshaft break-in lube and to use oil with lots of ZDDP. Stock valve springs are mandatory.

HeadTrauma said:

Indeed.. I used three spare OEM rockers I had and bought one new OEM one.
Also bought a new hotcam. Hotcam was like 145$ en the rocker 30$.
Just when I bought the stuff someone offered me a complete head for 100$ which I have bought as a spare set now.

Used grease with Mos^2 for assembly as that's what I normally use for engines. Checked today with a light and the cam lobes look fine thank god. But I did that after last rebuild also. Too bad I can't look under the rockers from the outside..  

I will take of the topend in half a year from now, just before I go on vacation with the bike. Then I'll see if it is worn again. Was thinking of taking this bike on a real long trip... like 1-2 months though europe.. but this cam failure destroyed this dream for me..

I wonder how much longer I would have ridden this thing if the timing chain didn't skip...

You know a lot of bikes use the same cam and rocker system. For example the tt600 I think and cb550 fours. You don't hear as much disaster story's about those bikes as this one.
The camlobes of the cb550 four turn in a large 'puddles' were oil collects. They don't have holes in the cam lobes as far as I know. Seems like they aren't as critical as the RFVC heads.

The xr600 head also has something that looks like 'oil puddles' but maybe they were designed too small or something...

Well... after about 2250km's since this rebuild, I took the head of yesterday because my headgasket blew. Turned out to be 3 headbolts loose. I used a cheaper fiber headgasket which I had lon the shelf. I think it's because of headgasket quality that the bolts loosened up after heating a couple of times.
Still drove 600km with it though! (thought it was an exhaust seal)

Before I had the cometic head gasket and had no problems...

I installed a 4AN stainless hose instead of the dinky oil line after the last rebuild, and the cam, rockers and cylinderwall are all looking perfect!
Pretty happy with that!
I'll put the engine together with ATHENA gaskets and the steel pressed head-gasket this time.

Otherwise the bike performed fine! It's pretty fast, I can keep up with the newer bikes and I'm faster on the longer sandy roads. :-)

Personally I don't use moly based assembly lube in wet clutch engines. Moly can make the plates too slick and not grab good enough even with heavy springs. It might be restricting or clogging your tiny paper oil filter too. If ya gotta use it change the breakin oil very early along with a new filter. Moly assy lube is best for flat tappet cams that need to rotate the lifters for maximum life. Engines that run rockers directly against cam lobes will do better with other assy lubes not conaining moly. Same for roller cam engines, no moly. A bad manual compression release cable or improper routing can pull the exhaust valve in just enough to contact the piston specially if oil gets low and the valves begin sticking cause of the heat and friction. Just my opinion but all that wear is pretty typical from low oil either from restriction or consumption.

Edited by valvesrule, 12 May 2012 - 09:18 PM.

valvesrule, on 12 May 2012 - 09:06 PM, said:

I don't know what caused the problems I had half a year ago... but this time everything is fine after 2250km thank god...
Maybe the oil pump feed line was kinked and it starved oil flow... but my nicasil was..and still is absolutely flawless and so was the middle bearing of the camshaft. But perhaps those were splash lubricated...
I do have a bigger line to the head now, but with the old banjo hole sizes in the adapters.. gives a bit more oil to the head when the oil is cold and thick. Maybe it doesn't do anything but it doesnt hurt either.
I'm going to install a AN6 line between the frame reservoir and the oil pump instead of the stock line to be shure it does not get restricted.

When I was doing the enduro event half a year ago in which the valve hit the piston I had a crash just before the I noticed the engine got f*cked. I think my throttle and decompression cable were pulled because they hooked under my steering-stop. I remember my throttle cable being f*cked and I got the problems directly after that.

So I guess you are right and I did pull the decompression valve in during the crash and it hit my piston..

Ilja, on 14 May 2012 - 08:25 AM, said:

Learned from experience. Had a 600 that would die every time you turned the bars left. After thinking it must be a bad electrical connection losing contact when turned and going thru all the terminals I noticed the compression release cable was tight, disconnected it and the problem was gone. Probably was a cable from a 185 or such. I got lucky with no damage to engine parts.

valvesrule, on 15 May 2012 - 11:34 PM, said:

I've had 3-4 XRs in the garage with the same problem, misrouted cable.