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rockieman

Mr. Valve meet Mr. Piston

16 posts in this topic

I finally got around to tearing my motor down on my 400 ('99) this weekend. It blew on me about a month ago..... as I suspected I dropped a valve on the piston.

http://i14.photobucket.com/albums/a306/rockieman01/wr400%20motor/IMG_2080.jpg

I was able to dislodge the valve which disclosed a hole in the top of the piston. Looks like a new head is in order as well....the seat for the valve that broke got hammered pretty good.

http://i14.photobucket.com/albums/a306/rockieman01/wr400%20motor/IMG_2077.jpg

In order to keep my cost down I'm thinking I'll stay with the standard bore and just replace the piston. I'm looking for suggestions on what I should do with the head? New? Ebay?

I also would appreciate input on whether or not I should split the cases? When I drained the oil it was like new....only had 30 miles on the last change.

Thanks in advance for your input!

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Time for a full rebuild. New head, valves, piston, bore & coat the jug, new crank and timing chain. Clutch baskets most likely are notched and all new engine seals. :banghead:

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Time for a full rebuild. New head, valves, piston, bore & coat the jug, new crank and timing chain. Clutch baskets most likely are notched and all new engine seals. :banghead:

OEM or aftermarket? I have to think there are better options for the valve train..... probably won't replace the clutch since I have a fairly new Revloc. The bike has about 8500 miles....

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You can do it a s cheaply as you can. aftermarket or stock parts. Keep in mind that the cam chain tensioner needs replacing, new cam chain and since the crank has the sprocket machined into it , a new crank and bearings is needed. The cam crank sprocket will be hooked. :banghead:

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A few questions to the original poster:

1. What was the mileage on that motor?

2. How was the bike ridden?

3. Was holding the manual decomp in while the engine was running cause the valve to penatrate (huh...I said penatrate) the piston?

4. What that motor properly maintained?

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A few questions to the original poster:

1. What was the mileage on that motor? 8500 miles

2. How was the bike ridden? trail riding only

3. Was holding the manual decomp in while the engine was running cause the valve to penatrate (huh...I said penatrate) the piston? never

4. What that motor properly maintained?

oil changed religiously, valves checked regularly, I had less than 300 miles on my last valve adjustment, 30 miles on the last oil change

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Thanks for your reply Indy....couple of other things come to mind while I'm in there. Water pump shaft, bearing and seals? Transmission? All the gears or should I inspect them first and order accordingly? I plan to replace the cam chain and tensioner if necessary. Any other chain related items?

Thanks again,

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Thanks for your reply Indy....couple of other things come to mind while I'm in there. Water pump shaft, bearing and seals? Transmission? All the gears or should I inspect them first and order accordingly? I plan to replace the cam chain and tensioner if necessary. Any other chain related items?

Thanks again,

I believe I would wrap a new bike around that new engine. :banghead:

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Your transmission should be fine as long as it shifts well. If not you may need to look at the shifter forks and drum. I rebuilt my 450 after 12,000. miles and the tranny was fine. You have to split the cases you might as well put in a new counter shaft bearing and seals. The water pump only needs new seals the bearing should be fine. It would be a shame to partial rebuild her and have her break down soon there after. Take your time and do the crank on up and you will should another 8,500. miles out of that engine. :banghead:

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Here is what it can cost to rebuild:

Bore and recoat the jug and coat the new piston: $350.

New bottom end crank, cam chain and seals & bearings: $450.

Complete top end overhaul with valves, cut new seats: $525.

I spent nearly $2,000. in parts on my full rebuild with complete clutch and baskets. Well worth it if you plan to keep her for another 10,000 miles. :banghead:

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I finally got around to tearing my motor down on my 400 ('99) this weekend. It blew on me about a month ago..... as I suspected I dropped a valve on the piston.

http://i14.photobucket.com/albums/a306/rockieman01/wr400%20motor/IMG_2080.jpg

I was able to dislodge the valve which disclosed a hole in the top of the piston. Looks like a new head is in order as well....the seat for the valve that broke got hammered pretty good.

http://i14.photobucket.com/albums/a306/rockieman01/wr400%20motor/IMG_2077.jpg

In order to keep my cost down I'm thinking I'll stay with the standard bore and just replace the piston. I'm looking for suggestions on what I should do with the head? New? Ebay?

I also would appreciate input on whether or not I should split the cases? When I drained the oil it was like new....only had 30 miles on the last change.

Thanks in advance for your input!

Are you sure you're not working on a Honda. ...they are more prone to this problem than the blue thumpers :banghead: J/K that really sucks bro. Let us know how much $$ so we won't be shocked if/when it happens :banghead:

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Are you sure you're not working on a Honda. ...they are more prone to this problem than the blue thumpers :lol: J/K that really sucks bro. Let us know how much $$ so we won't be shocked if/when it happens :banghead:

That could happen to any of these 4 stroke racebikes, they just happen sooner on the CRFs :lol: . My cousins 2001 YZ 250f burnt the valves after an ungodly amount of hrs. Somthing close to 350 *amateur racing* hrs. The original owner checked the valves around the first 50 hrs. and didn't touch them afterwards. Well they bit the bullet on the rebuild and after 20 hrs all 5 valves haven't moved at all. These 5 valve yamis are amazing :banghead:

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