416cc 87mm Top End Rebuild Problems. - Honda TRX Forum
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post #1 of 12 Old 05-12-2019, 05:37 PM Thread Starter
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416cc 87mm Top End Rebuild Problems.

Hello all, I am having problems getting the ring gap in specs per service manual on a brand new wiseco 87mm piston kit. I took my jug to a reputable shop and had it bored at .002 clearance with the piston. Put brand new rings in the cylinder to check clearance and its out of spec at .017 top ring, .023 second ring. Manual says I need .008-.014 for top ring, .014-.020 for second. It is however within service limits which is .020 for top, .026 for second so I decided to run with it and guess what, it lost compression during first two minutes of running during break in. Took it all back apart and nothing is damaged, rings still have the same gap as before running. What to do now? Maybe order a set of 88mm rings and file the ends down to spec? I assume I have to go with wiseco rings for a wiseco piston correct?
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post #2 of 12 Old 05-12-2019, 06:46 PM
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Your loss of compression was not due to the rings - I would have done a cylinder leak down before taking it back apart

That being said, Why didn't you have the shop that bored the cylinder set the ring end gap? I bore cylinders and typically set the clearance at .0015" unless the owner says he's going to race it, then I set the clearance at .002" - and, yes your ring end gap is within spec for an 85 mm bore - if you check the papers that came with the Wiseco piston, for a bore of 87 mm (3.425") the top ring is correct at .0137" and the second ring is correct at .0171", but for high performance engines, the top ring is correct at .0154" and second at .0188" and for extra high performance (using a turbo or Nitrous , the top ring end gap would be set at .0171 and the second ring at .0188.

Yes, a Wiseco piston has to have Wiseco rings. No, you can't get 88 mm rings and file them for proper end gap in an 87 mm bore - the tension of the rings will be too great and the rings will press into the cylinder wall too hard.

The questions I would like answered is; how was the engine run during the first two minutes? Idle only, moderate throttle 1st, 2nd and 3rd gear, wide open throttle and were the rings installed right side up? Although you had the engine bored, did you do anything else? Did you use the 10:1 or 11:1 compression ratio piston? High lift cam? What was the clearance between the piston crown and the valves?

I will guess the problem was the cam jumped time and you bent the intake valves.
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post #3 of 12 Old 05-12-2019, 09:02 PM Thread Starter
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Thanks for your reply, It didn’t even dawn on me to give the rings to the machine shop, they didn’t ask for them either. the cam gear was still timed correctly upon disassembly and the valves never touched the piston, neither had marks but the piston top had a quite a bit of oil thats why I figured the rings were the problem letting oil by but not sure now. I did forget to check valve clearance after it lost compression so maybe a valve did tighten up too much and started to not close during breakin. I’m using 10:1 piston with stock cam. I was following break in procedure that partzilla posted on YouTube. First let it run for a couple mins up to temp varying RPMs then shut off, Let it cool down completely Then rode it 1st-4th gear varying load 1/4 to 1/2 throttle staying away from high rpms. Rode for less than 2mins before it died loosing all compression.
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post #4 of 12 Old 05-12-2019, 10:01 PM Thread Starter
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So these compression ring gaps should be fine? I haven’t checked the oil ring gaps yet. I guess I’ll reassemble at TDC and double check Valve lash, maybe something wasnt seated properly when I set them before running. I had the ring markings “N” facing upwards so pretty sure that was all good. Am I ok reusing gaskets with only 3- 4mins run time?
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post #5 of 12 Old 05-13-2019, 02:38 AM
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With oil on top the piston I would be concerned about the oil ring. It's pretty easy to get the oil ring wrong. The expander ring needs to have the ends butted and not overlapped. Also, the expander should butted on the intake side (call it 12 o'clock) while one oil rail should be gapped at the 4 o'clock and the other rail at the 8 o'clock. The compression rings are installed with the marked side up (you did it right) and the black ring gapped at the 10 o'clock (or 2 o'clock) and the top ring (chrome faced - white or silver edge) gapped at the opposite position of the second ring.

Reusing the gaskets is your call - I personally always use new gaskets - when I order a big bore kit, I always order a spare set of gaskets just in case or so I will have them the next time I need them.
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post #6 of 12 Old 05-13-2019, 03:17 AM Thread Starter
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Yep, I made sure the spacer was butted and all the gaps set to 120 degrees or so per the manual and piston booklet. Just don't know what to do with these rings. It pisses me off to have brand new rings with new bore not in spec. I don't have a super accurate micrometer but have a digital caliper and it shows piston is exactly 87.000mm. Seems like Wiseco dropped the ball on this piston and should have made it something like 86.90 to make sure the rings will be in spec after the jug is bored for clearance. Oil may have dripped on the piston when I was pulling the head off because it was clean oil, not burnt. I cranked it over with valve cover off to make sure oil pump was working and oil flooded the head pretty quick so I'm sure that is good.

Its really frustrating that this is the second time rebuilding my top end and loosing compression within minutes. First time I bought a complete 416cc top end kit from ebay with a new china jug, wiseco piston kit that came from a race shop where they supposedly checked everything and was complete & ready to bolt on. Well that only lasted a few minutes as well before loosing compression too. Took it apart and found the Wiseco piston was stamped on top as 87mm but measured 89mm, Jug was bored to match piston at 89mm, rings were for 87mm kit. Thought it was the cheap china jug that was the problem but nope, Wiseco dropped the ball on this one stamping the wrong size piston. There QC must be going down hill. The race shop was nice enough to resend a new 87mm piston kit and refunded the jug money so I could bore the stock cylinder which I thought would be better but it didn't work worth a shit either. I've done a bunch of 2-smoke top ends and never had any trouble with new parts not working.
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post #7 of 12 Old 05-13-2019, 12:55 PM
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You are having a run of bad luck, but I don't think it's piston or ring related.

You need to look at the valves and rocker arms - possibly the auto decompressor is sticking causing an exhaust valve to be held slightly open.

I'm not there to see the parts, but I think before putting it back together you should investigate the valves, decompressor and rocker arms. Then if you put it together and have it lose compression again, do a cylinder leak down to find out where the compression is going.
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post #8 of 12 Old 05-14-2019, 04:37 AM Thread Starter
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Is the auto decompression really needed for an electric start? Is there an easy way to bypass it in case that is the issue? I don’t understand how that little pin/spring releases compression.
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post #9 of 12 Old 05-15-2019, 02:24 AM
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I just did a 416 rebuild on my 04. The machine shop I sent my cylinder to in Davenport IA would only gaurntee there work if I sent the piston and rings with the cylinder. Also I suggest getting rid of the decompression mechanism as the starter has plenty of power to turn the motor over even when hot. I have a 10:1 wiseco and put a stage 2 hot cam in and rejetted with an open air box running a uni filter with a big gun exhaust. The quad rips now, it will pull the wheels of the ground on a top speed run in third gear with stock gearing.
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post #10 of 12 Old 05-15-2019, 01:19 PM Thread Starter
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Aright, all this mess was indeed valve related. I feel dumb now for taking the jug off. I reassembled everything and the right exhaust valve was way too tight causing the valve to not close, Spun it over a few times and put at TDC, Adjusted intakes .004, Exhuast .005, and it had great compression again. Rode for 2 mins and it started running bad and sounding like a Subaru. Checked Valves again at TDC, intakes were good, Both Exhaust valves had tightened up with zero play! Re-adjusted to .005, now running good again but got too late to ride to see how long it would last, The cam, rockers, and valves all looked good with no excessive wear, Why the heck are my exhaust valves keep tightening up? Does that mean they are sinking into the valve seat?
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