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Discussion Starter #1
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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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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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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Discussion Starter #4
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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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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Discussion Starter #6
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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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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Discussion Starter #8
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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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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Discussion Starter #10
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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Discussion Starter #11
Rode around again for about 10-15min and rechecked the valves and they didn't move this time, maybe there was just some carbon on the seats that had to hammered in. Felt a nice increase in power with the 416cc kit too, just hope it lasts this time.
 

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How long does it typically take for rings to fully seat? I'm still on the first tank of gas and I am seeing a little bit of smoke out of the pipe when I let off the gas after a high rpm run in 3rd or 4th gear. I'm hoping this is only because the rings are not fully seated yet.
 

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How long it takes for rings to seat varies on many factors; the grit of the stones used for final honing, the brand of piston & rings, the set clearance of the piston to cylinder, the brand, viscosity and type oil used, and engine operation.

The engine should not be operated above half it's rated optimum RPM for the first 20 to 30 hours of operation. Heating and cooling cycles are critical for proper break-in. Starting and engine an letting it run at a steady speed for 30 hours continuously is not considered broken-in. It is best; started, let idle about 5 minutes, run at moderate speeds for 15 to 30 minutes, stopped and allowed to cool for 2 to 4 hours then repeating the cycle about 8 times.

This is not saying that the throttle cannot be opened fully - it just means the engine should not be operated above 1/2 it's rated maximum rpms. Punch the throttle, at about 1/2 maximum rpm, back off the throttle and coast to slow. This can be done in every gear. It's as important for the engine to be pushed by deceleration an it is for the engine to pull the vehicle up to speed.

The two bad things you can do to a fresh engine is to let it sit and idle for more than 5 minutes and operate at high rpm - the worst thing you can do to a new engine is to take it out on a road and operate at a steady throttle in any gear for more than 30 seconds at a time - running it at top rpm for any period of time before it it broken-in is inviting disaster.

A break-in will take more or less time depending on the oil selected for the initial operation. Normal break-in should be done with the oil that is intended to be used regularly. A fast break-in may be obtained by using 5w30 mineral oil - an extended break-in will be necessary if using synthetic oil (may take up to 10 times as long for complete break in) - whatever oil is used for break-in should be rated JASO MA or MA2. Break-in on engines with plated cylinders is very short compared to cast iron or steel sleeved engines.

With all that being said; it is normal for any engine to 'puff' smoke when run up to near maximum rpm and then backing off the throttle either for shifting or deceleration. Engines with high compression pistons are more susceptible to puffing due to high vacuum caused when the throttle is closed suddenly - oil may be pulled up past the rings or down from the intake valves.

The smoke may be diminished (although not necessarily eliminated) by raising the idle speed (decreasing the vacuum when the throttle is closed) and using synthetic oil after break-in.

Example: in 1975 I rebuilt the engine in my 65 mustang - I had it bored .030 oversize, installed 12:1 compression ratio Thompson race pistons with 'double' moly rings (both the compression rings were chrome faced) and I used 351 Windsor heads which had a larger chamber dropping my final compression to about 11:1, but had larger valves which allowed the engine to breathe better and raised my red line from 6000 rpm to 7000 rpm - I filled the engine with PENNZOIL 20w50 and began the break-in - after 5000 miles, the engine was still using about a quart of oil every 1000 miles - I talked to a race tech at Ford, told him all that I did and his first question was 'what kind of oil are you using? I told him and he said that was my problem - 'the oil was too slick' - Pennzoil was paraffin based, he suggested switching to Quaker State 10w40 for break-in because it was wax based and would allow for faster break-in - reluctantly I switched, within 1000 miles the engine quit burning oil - I switched back to Pennzoil and the engine used less than a half quart in 3000 miles - by the time I had 20,000 miles on the engine, the oil consumption was negligible, but it would puff between shifts when revved up to 7000 rpm before shifting.

Give it some time and I think the problem may take care of itself - if it gets worse, have the head rebuilt - at least new valve seals and possibly new guides.
 

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Discussion Starter #15
Cool, I hope you are right about it fixing itself. I did replace the valve seals while I already had the head off with OEM parts. I checked the compression to make sure these rings were ok and got 165psi! I had no idea a 10:1 Piston would raise compression that much. Stock specs are `100-128psi. Regarding break-in time, I think 20-30 hours is extremely conservative on a motorcycle/atv. I found a break in procedure on Wiseco's site and they stated rings should be seated after 6 heat cycles with about an hour total run time.
 

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Considering cool down takes an hour or more (for a complete cool down on a hot day) and at least 20 to 30 minutes to get up to normal operating temp it's definitely more than you can squeeze in in an hour. And I'm used to working with .001 to .015 clearances on stock engines that are designed to run for years without need to tear them down again. Race engines are put together looser, but are rebuilt or serviced more often. A race engine breaks in fast and wears out fast, but it's a cost of racing.

Typical compression on a 400EX is about 120 to 150 depending on the gauge, condition of the battery and starter motor and valve clearances. 165 is good - it just means you definitely need 93 to 94 octane fuel, but anything over 95 is probably too high. My CRF has a stock 12.9:1 compression ratio and calls for 93 octane - your stock compression ratio (9.1:1 called for 91 octane) - my CRF runs hot and loses power above 94.5 octane - I tried running 100 octane VP Racing fuel one time and noticed a considerable loss of power.

Let me know how it works out with some run time on it.
 
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