Bent Intake Valves - XR400

[JKTrevecca]

I picked up a 400 for $600 that won't run. Got it torn down and it has jumped time and bent the two intake valves. Exhaust valves are okay and hold fluid when poured in the exhaust ports. I talked to the prior owner who said the bike did *not* smoke or burn oil before this occurred. The piston is okay. It's not dented at all. There is just a very slight mark on the top of the piston from where it impacted the valve. I can still see the factory hash-marks on the cyl walls with no verticle scoring.

Can any of you offer your thoughts/experience/wisdom regarding the following questions I'm tossing around in my head? 

1. If I purchase replacement intake valves, can I lap them to the existing seats with success or is re-cutting the seats necessary? Anybody on here done this before w/o re-cutting the seats?

2. I believe the reason for the jumped time is due to the timing chain having a manual adjuster on it that was no-where close to tight enough. The prior owner said he never touched the adjuster in the 2 years he owned the bike. During my tear down, I found the adjuster to be a full inch further away from the chain guide than it should have been. This leads me to the following question. Is there a way to tell whether the current chain is okay w/o removing it? If so, how can I tell? I tightened the tensioner and rotated the engine and the current chain appears to be okay. Can it be measured w/o being removed? Any thoughts on this are welcome. If there is no way to measure it w/o removing it then I'll plan to simply replace it. I'm just trying to avoid pulling the side cover if I don't have to and replacing the chain requires the side cover be removed - Correct?

3. Since the prior owner said the engine didn't burn oil, I'm considering *not* replacing the cyl and piston. Thoughts? If I do replace the cyl and piston, would you suggest a stock bore or the 440 kits sold on ebay? Any luck with those? Problems with those? I can buy a complete kit for $60 it appears! Sounds too good to be true.

I am a very casual rider. Just riding around the fields and farms and trails. I'm not a racer so I don't need max power or performance. Just need a bike that runs and thumps.

Thank you! Happy riding!

Edited October 27, 2018 by JKTrevecca

[chrisso]

If it was my bike ,and it is how you describe, then I would pull the bent valves out ,check whether the valve guides are ok and not cracked ,if there good then there's a good chance that new valves and a lap job will be good enough , tension the chain and ride

[Trailryder42]

After you the tension the cam chain adjuster to take up the slack, is there any adjustment left in it?

What year model XR? If you think the amount of hours on the engine are in the neighborhood you could expect for the year model or there's no adjustment left in the adjuster, replace the cam chain. Yes, the side cover has to come off.

There's not a pin to pin length wear spec for the chain.

I'd get new guides and seals for the 2 new intake valves. I'd take a close look at the old intake valves and seats for amount of wear where they mate. If they don't look bad/worn, you may be able to get away with lapping.

[BOAB]

When I did the big bore top end on my 250 I installed Wiseco SS valves.  I lapped them in with no problem.  Having new seats cut is not always necessary.

[JKTrevecca]

Thanks for the replies/thoughts.

I ordered Wiseco valves and installed them into the head yesterday. The first one, I lapped, installed, and poured acetone into the runner. The acetone very very slowly seeps past the closed valve. The second valve I installed without lapping and ZERO acetone seeps past that valve.

I'm wishing I hadn't lapped the first one! Now I'm debating whether to lap the seeping valve a bit more, leave it alone and put the engine back together, or take it to a machine shop. It takes about 10 seconds for a visual indication of leaking acetone to show up.

WHAT WOULD YOU DO?

I went ahead and bought a new timing chain. I read about and figured out a way to install it w/o removing the side cover! Basically, I'll be connecting the old and new chains, fishing the new chain around the crank pully and back up to the top, re-connecting the new chain to itself, and whala! Anybody else done it this way?

 

Looking forward to your thought on the ever-so-slightly leaking intake valve.

 

-- Jason

[Trailryder42]

Curious to know how the first valve sealed "before" lapping it.

So you're going to break the new chain to fish it onto the lower sprocket?

[JKTrevecca]

1 hour ago, Trailryder42 said:

Curious to know how the first valve sealed "before" lapping it.

So you're going to break the new chain to fish it onto the lower sprocket?

I have no idea how/why the valve that I didn't lap sealed when the one I did lap has an ever so slight leak in it. I can still lap that one but since it sealed w/o lapping when the other one didn't seal with lapping, I'm considering *not* lapping the 2nd valve. I may run the head by a machine shop and have them vacuum check it first.

Yes - I'm going to break the new chain, connect it to the old, then re-connect it to itself after fishing it through and around the crank sprocket. I have a tool made to press the pins in/out of the chain links.

-- Jason