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Discussion Starter #1
Ok so where do i start, i am not going to mention shop names as they are all real reputable engine builders and am pretty sure whats been going on is not their fault. So when we first built this 840 with dasa cnc heads +1 valves. Ran great for about 2 trips. Then i broke the front cyl cam chain bent all 8 valves. Rebuilt it and withen in 1 trip started to mushroom the valves tip. Replaced all 8 valves again last 3 trips and sucked a valve down and of course bought all 8 again but now the other builder put lash caps thinking the valve angle might be wrong,while it was down i decided to put good rods in it. Well after3trips broke the reat cam chain. After the 1st one broke i called fst since it was his 840 kit(not bad mouthing) i just wanted info he said its never happened to him and that he could only think of 1 time he as heard of this happening. My ? Is what iam i missing here everyone tells me this is so rare and here i am with 10k(after all the rebuilding and parts) in a teryx motor and 2 broken cam chains which i am sure bent all the valves again. I know people have a lot of knowledge on this website just need help thank you for any info
 

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Hmmm

Its very rare to actually break a cam chain on these motors... Normally if any one breaks its the jack shaft chain which drives both the cam chains.

Several things you can check though...

Rockers - Inspect and make sure they're moving freely because the easiest way to break a chain is for these to bind putting to much load on the chain.

Cams - Whos cams are you running? Are the valves bottoming out and binding from to much lift?

Valve springs - whos valve springs because you could have wayyyyyyy to much tension.

Cam chain sprockets themselves - over time they'll get sharp edged.

Now I'm curious about the heads... is it wearing out ALL the valves or just the intakes? Its pretty damn rare to wear out an exhaust valve in these motors. Are they all +1? Who makes them and are they stainless steel valves/titanium or what? Take it to a reputable engine machine shop near by and have them re-cut the seats.


Chains a chain... If its breaking then something is putting to much load on it and that revolves around what its rotating.

Though, why did the motor bend all 8 valves if only one cam chain broke? Shouldn't have gotten the other cylinder.
 

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Discussion Starter #3
All the valves have been kibble white valves, yes it would mushroom all the valves the intakes more. I dont remember what springs and retainers we put the last time but they were but they were expensive like 300.00 i dont remember the name but they were out of hesperia ca, i wanna say like (rev tek or high rev) somthing like that. I BELIVE IT WAS A WEB 214 OR 241 CAM AND THERE LONGER ROCKER PADS. AS FAR AS THE SPROCKETS THEY GOT ABOUT 50 HRS GOING OFF THE CAR HR METER. I DONT KNOW IF ANYBODY HAS CHANGED THEM WITH ALL THE REBUILDS THANK YOU FOR ALL THE GOOD INFO
 

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Valve spring coil bind makes the most sense to me.
I agree, though you would think there would also be wear on the cams/rockers or at least should be.

Personally, I'd just purchase a set of kibble weight double valve springs for $100 that everyone has been running for a decade now. FST/AMR/FCP all sell them and I run them in all the motors I build as well with no issues.

Who sold you the cams... I know a lot of the web numbers but its hard to keep track of them all because everyone uses web for their cams.

Also I'd take the head to a reputable engine machine shop around that does race engines for trucks/cars and have them check the seats on the heads to try and find out whats going on with the mushrooming... something is definitely not right.
 

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did you use the Kibble White +1 valves if so they have had lots of issues with those +1 valves u arent the first,you are prob just running longer than most that had this issue because on the ATV you can hear the valves out of spec prob alot easier than you can on a teryx being the motor is covered,but those =1 will mushroom on the tops and it makes you lash so great and finally bomb,and being a 840 makes it worse it runs so much harder,get a set of the custom +1.5mm valves from a builder no issues I got those and havent had any issues but seen lots with the +1s hope this helps
 

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Valve mushrooming is wrong valve spring, seen it 4-5 times now. When the valves float they slap against the seat and mushroom, there is no other way valves can mushroom. Take care of that problem and the other problem should disappear.
 

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Call Big Kevs Performance and he can explane,the valves are mushrooming on the tops cuasing to much clearance and trashing your motor,anyone I have spoke with about the +1 kibble white valves has had this issue,go over to Kwieriders and do a search on +1 Kibble White Valves,I bet this is the prob for sure,if you r running stage 2 or 3 cams or even 4 all you need is the Kibble White Dual valve springs,I have a 840 drag motor with Stage 4 Cams and Kibble White dual valve springs and the Web extended rocker pads no issues at all not 1!
 

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I am talking about the top tips mushrooming on the valves not at the seats,when the tops mushroom ,think how much valve lash clearance you r getting,BOM
 

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Discussion Starter #10
sorry its taken so long for me to write back been busy at work. and i am also sorry about the post head line as i did not break a cam chain this time, i just guess that out in glamis when i pulled the inspection plates and the valves did not move as i cranked the motor. it broke the cam compression release weight on the cam gear. so know i am buying new cams with those gone from web cam. back to the valves, yes they were kibble white +1. after two trips(maybe 4hrs on the new valves) some of my lash caps is almost worn to nothing. the installed height on the valves was .020off what they call for so thats 1 prob for sure. i am going to use 1.5 valves now. ill keep you guys posted on what else i find
 

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yep thats what I was talking about the tips wearing out so fast,get those +1.5s and dont look back you will be fine,and Web will do any cam for our motors with no decomps,but make sure to keep a full battery,if really low with no decomps it will cuase the motor to kick back and Breack teeth on the starter gear behind the flywheel,just replaced that gear on a AMR 730 with XX cams no decomps,battery was almost dead and he was trying to start it and $#&%#&%& gear broke 2 teeth off,needed a few seals anyway so replaced it all takes about a hour on the quad sure longer on rex do to where the motor is.
Let us know when you get it straight and how it runs!
 
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