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Discussion Starter · #1 ·
I have a 2003 400ex with a fresh top end new valves, cam, timing chain, and piston. I have had no issues with it since the rebuild approximately 15 engine hours ago. I replaced the valve cover gasket with a metal one since the paper one I installed during the rebuild was leaking, and I readjusted the valves after as a precaution. But when I went on a test ride to check for leaks it ran strong for about 2 minutes then shut off on me randomly under normal riding conditions nothing strenuous. When I pulled it apart it had bent both exhaust valves the left worse than right. What could of caused it I adjusted it at what I thought was tdc on the compression stroke and it ran fine when I started it up to warm up no weird noises whatsoever. Please help I can’t think of anything else that could of caused it.
 

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Very difficult to say - you did not disclose the specifics:

What brand of piston?
What compression ratio?
What brand of valves?
What was the valve stem to guide clearance?
Did you install new valve stem seals?
What did you lube the new valve stems with?
What type of engine oil are you using?

Now while the causes are many, there is about only one reason for the valves to be bent - valve to piston contact.

What caused the contact? Valve stuck in a guide, cam jumped time, valve float (happens at extreme high RPM), improper valve assembly, broken valve spring, rocker arm binding or seized on shaft, improper assembly of the rocker arm assemblies, engine overheating (caused by extended idling or low speed operation, grade of fuel, lugging the engine or lack of lubrication) - perhaps oil pump failure or cam chain tensioner failure.

BTW - welcome to the forum
 

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Discussion Starter · #3 ·
Very difficult to say - you did not disclose the specifics:

What brand of piston?
What compression ratio?
What brand of valves?
What was the valve stem to guide clearance?
Did you install new valve stem seals?
What did you lube the new valve stems with?
What type of engine oil are you using?

Now while the causes are many, there is about only one reason for the valves to be bent - valve to piston contact.

What caused the contact? Valve stuck in a guide, cam jumped time, valve float (happens at extreme high RPM), improper valve assembly, broken valve spring, rocker arm binding or seized on shaft, improper assembly of the rocker arm assemblies, engine overheating (caused by extended idling or low speed operation, grade of fuel, lugging the engine or lack of lubrication) - perhaps oil pump failure or cam chain tensioner failure.

BTW - welcome to the forum
Thanks, I didn’t use top quality parts this time as I was under a time constraint and on a budget but the piston I used is linked below I couldn’t find the compression ratio for it in the listing and the valves are Motoku I bought just about all of it off of Amazon I never measured the stem to guide clearance didn’t even know I should have. All valve stem seals were new and got lubed with Napa engine assembly lube. I also ran Honda recommended break in oil GN4 but I used 10-30 for my climate. The valves were all free less than an hour before the incident. I wasn’t running high rpm. All new springs and they were fine after disassembly. engine wasn’t even warm at the time i pulled it apart less than 5 minutes after it bent and it wasn’t even that warm and I checked the oil pump for proper flow after.

All that said I tried reassembling it today after getting new valves and it all went together perfectly up until the tune up and I couldn’t get the left hand intake valve to get any clearance no matter what I did the rocker was free timing was dead on and the right intake valve had plenty of clearance but on the left I could back the adjustment screw all the way out and still had no clearance the rocker itself was pressing against the valve. Could it be my cam was damaged during the bending or rocker arms?
Piston- NICHE Gasket Piston Ring Spark Plug Kit Combo for Honda 1996-2014 TRX400EX TRX400X XR400R 13011-KCY-670 https://www.amazon.com/dp/B07GT84P7...abc_5YKW15H83N0KVDD06TRN?_encoding=UTF8&psc=1

Valves-MOTOKU Cylinder Intake and Exhaust Valves kit for Honda Sportrax 400EX TRX400X XR400R 1996-2008 https://www.amazon.com/dp/B08SJ2LS4...abc_HPQWPKKHCCEF05175AJ4?_encoding=UTF8&psc=1
 

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Discussion Starter · #4 ·
Well I think I may have solved my tuning issue and possibly why it bent the valves is it possible that my cam sprocket flange could have rotated on the cam because when I look at orientation online it looks completely different than mine currently
Automotive tire Coil spring Motor vehicle Automotive design Household hardware My cam


Automotive fuel system Automotive tire Motor vehicle Automotive design Automotive exhaust one I found on YouTube
 

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Thanks for the info - the piston is std. compression (9.1:1) and although Amazon parts are the cheapest the Chinese produce, they normally hold up for a couple of years. I build engines for a living and routinely check the finest details.

In looking at the pics, I think you are right about the cam. If you check the old stock cam against the new cam you will find at TDC the lobes point downward at approx. the 4 and 8 o'clock positions. If the flange moved, I would not reuse that cam and would file a complaint with the seller (Amazon may have brokered the deal and the seller was a third party) or with Amazon (whatever is necessary to return the cam) and then don't buy the same brand of cam. I have removed and reinstalled the flange from stock cams - it is splined and cannot move!
Product Font Line Auto part Parallel

It's simply an example of the poor craftsmanship of some of the Chinese manufacturers.

Also, what is the red stuff on the gasket surface? Grease or RTV? Either way, the sealing surface should be clean and dry when the new shim is installed (the gasket is a shim and provides for proper bearing clearance when the parts are assembled and torqued as specified) - clean and dry is necessary for the coating on the shim to seal as designed.

With the cam lobes positioned as described you should be able to set the valve clearance. In addition; the oil you selected is perfect - when installing other than Honda valves, the stems need to be measured and compared to the OEM stem diameter. Normally Kibblewhite & Wisco valves are spot on the specified dimension of 5.480mm intake and 5.460 exhaust. Vertex, Faction MX and Hot Cams valves are within the tolerance of 5.475 - 5.490 and 5.455 - 5.470, but I have found Bronco and Shindy valves with stems larger than 5.495 and 5.475 requiring reaming or honing of the valve guide. New valves should be lubed with a molybdenum lubricant - I use DuPont Molykote D-321 R Anti-Friction in an 11 ounce aerosol can - it's $52 a can from McMaster-Carr industrial supply, but I only use a can every couple of years. You can also use Dri Slide Multi-Purpose which is available in a 4 ounce bottle for $10 or any lithium based moly grease.

A new cam should be lubed with a special break in lubricant and a new cam should never be installed without installing new lifters (or in the case of the TRX400) new rocker arms (not new sub-rockers). I use Comp Cams (UPC number 36584010074) in a 4 ounce bottle from O'reilly Auto Parts for $13.

I understand your enthusiasm and urgency to get going ASAP at as low of cost possible, but you will find out (as I did) it's cheaper to use quality parts spend more time to assure it is correct the first time than to have to fix it multiple times.

With the information you provided, I suspect you (with the help of YouTube) discovered the cause of the problem and are well on your way to rectifying the issue.

If you need any help or advice, please ask because I am Here 2 help (if I can).
 

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Discussion Starter · #6 ·
Thanks for the info - the piston is std. compression (9.1:1) and although Amazon parts are the cheapest the Chinese produce, they normally hold up for a couple of years. I build engines for a living and routinely check the finest details.

In looking at the pics, I think you are right about the cam. If you check the old stock cam against the new cam you will find at TDC the lobes point downward at approx. the 4 and 8 o'clock positions. If the flange moved, I would not reuse that cam and would file a complaint with the seller (Amazon may have brokered the deal and the seller was a third party) or with Amazon (whatever is necessary to return the cam) and then don't buy the same brand of cam. I have removed and reinstalled the flange from stock cams - it is splined and cannot move!
View attachment 4848
It's simply an example of the poor craftsmanship of some of the Chinese manufacturers.

Also, what is the red stuff on the gasket surface? Grease or RTV? Either way, the sealing surface should be clean and dry when the new shim is installed (the gasket is a shim and provides for proper bearing clearance when the parts are assembled and torqued as specified) - clean and dry is necessary for the coating on the shim to seal as designed.

With the cam lobes positioned as described you should be able to set the valve clearance. In addition; the oil you selected is perfect - when installing other than Honda valves, the stems need to be measured and compared to the OEM stem diameter. Normally Kibblewhite & Wisco valves are spot on the specified dimension of 5.480mm intake and 5.460 exhaust. Vertex, Faction MX and Hot Cams valves are within the tolerance of 5.475 - 5.490 and 5.455 - 5.470, but I have found Bronco and Shindy valves with stems larger than 5.495 and 5.475 requiring reaming or honing of the valve guide. New valves should be lubed with a molybdenum lubricant - I use DuPont Molykote D-321 R Anti-Friction in an 11 ounce aerosol can - it's $52 a can from McMaster-Carr industrial supply, but I only use a can every couple of years. You can also use Dri Slide Multi-Purpose which is available in a 4 ounce bottle for $10 or any lithium based moly grease.

A new cam should be lubed with a special break in lubricant and a new cam should never be installed without installing new lifters (or in the case of the TRX400) new rocker arms (not new sub-rockers). I use Comp Cams (UPC number 36584010074) in a 4 ounce bottle from O'reilly Auto Parts for $13.

I understand your enthusiasm and urgency to get going ASAP at as low of cost possible, but you will find out (as I did) it's cheaper to use quality parts spend more time to assure it is correct the first time than to have to fix it multiple times.

With the information you provided, I suspect you (with the help of YouTube) discovered the cause of the problem and are well on your way to rectifying the issue.

If you need any help or advice, please ask because I am Here 2 help (if I can).
Thanks
 

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Still, it an unknown if the cam failed first and if it did why? I suspect the cam was binding in the head - from the pics the new cam looks to be in worse condition than the old cam. What do the rocker arm pads look like?
 

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Discussion Starter · #9 ·
Still, it an unknown if the cam failed first and if it did why? I suspect the cam was binding in the head - from the pics the new cam looks to be in worse condition than the old cam. What do the rocker arm pads look like?
the old cam was in there for only a week and previous owner had piston in backwards and bent the valves and took out the lobe it never made it past break in the rocker pads didn’t look bad and all bearing surfaces are good light damage on the top of the center bearing surface but that was caused by this cam after failure it was fine right before
 

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the old cam was in there for only a week and previous owner had piston in backwards and bent the valves and took out the lobe it never made it past break in the rocker pads didn’t look bad and all bearing surfaces are good light damage on the top of the center bearing surface but that was caused by this cam after failure it was fine right before
So the old cam was only a week old? Having the piston in backwards will not usually take out the valves unless the cam timing is off or the engine run at extremely high RPM or having a high compression piston in place of the stock piston.

If the cam was aftermarket, did you plastigage the center plain bearing? I wonder if the center bearing seized and caused the flange to strip the splines? It would be highly unusual, but not impossible, for the rocker arms to exert enough pressure on the cam lobes to cause the flange to rotate on the splines. The only other thing I can think of is the cam was simply not properly hardened after machining and suffered material failure. The cam had to be too tight for the cam sprocket to turn and the pull from the crankshaft forced the flange to strip the splines.
 
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