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Discussion Starter #1
I have a 2002 400ex and recently did a top end rebuild. I put in new rings for a 416 piston and new rocker arms. Seals and stuff too. I have already let idle For 20 minutes, cool. Then 1/4 to 1/2 throttle variation for 20 minutes, cool. What would my next step be to break in the new rings?
 

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Done - idling will over heat the rings - best way to break in is pasture riding - moderate speeds, accelerating, decelerating, loading the engine and unloading the engine. Of course heating and cooling cycles are important too. Modern materials and manufacturing techniques means break in is simply moderate engine speeds during normal operation for a few heat and cool cycles.
 

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Done - idling will over heat the rings - best way to break in is pasture riding - moderate speeds, accelerating, decelerating, loading the engine and unloading the engine. Of course heating and cooling cycles are important too. Modern materials and manufacturing techniques means break in is simply moderate engine speeds during normal operation for a few heat and cool cycles.
So I should just ride it like how I would? Just make sure I accelerate and decelerate a lot. How long should I do this and how many times before I change oil?
 

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Just ride normally avoiding letting idle more than 5 minutes when cold and more than a minute when hot and avoid revving to the rev limiter. You can give it full throttle, just don't rev it too high before shifting.

If you can only ride it 20 minutes a day - about 10 days. If you can ride it for 20 minutes 3 times a day about 5 days
 

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Thinking about putting a 87mm piston in my 400ex also. What size head gasket did you use? I have read everywhere that the stock head gasket will work. The only one you need to get a diff gasket for is the 426 and 440. Is this true?
 

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Discussion Starter #7
I just used stock sized head gaskets for my 416. I do not know for a 426 or a 440, but I don’t think the head gasket size would effect anything. I used a tusk top end complete gasket kit and it works good for me. I resurfaced everything too.
 

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I just used stock sized head gaskets for my 416. I do not know for a 426 or a 440, but I don’t think the head gasket size would effect anything. I used a tusk top end complete gasket kit and it works good for me. I resurfaced everything too.
Awesome. Thank you. I have the complete engine gasket kit. Bought a stage 2 cam and was just going to put a 11.1 piston in but have everything at work to bore so might as we'll put the 416 in it.. Also going to p&p the head.
 

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Special head gasket is needed for 88 and 89 mm bores - Cometic C7826

For all bores under 88 mm a standard gasket may be used
 

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On youtube the Partzilla guy has a video on engine brake in. I've done it his way for years and its worked great. The machinist who did the work on a chevy 350 block I did in the mid 1980s (my first rebuild on my own) pretty much told me the same thing... ring break in happens in the first 20 minutes, so you gotta get it right.

Also, use NORMAL oil for break in. Synthetic oils are too slick and you wont get a good break in. You'll end up tearing it back down and re-honing.

-DallanC
 

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Discussion Starter #12
On youtube the Partzilla guy has a video on engine brake in. I've done it his way for years and its worked great. The machinist who did the work on a chevy 350 block I did in the mid 1980s (my first rebuild on my own) pretty much told me the same thing... ring break in happens in the first 20 minutes, so you gotta get it right.

Also, use NORMAL oil for break in. Synthetic oils are too slick and you wont get a good break in. You'll end up tearing it back down and re-honing.

-DallanC
I watched a Partzilla guy and he said to idle for 30 cool 1/4-1/2 throttle cool then ride it for a while, then change oil. I already did up to the 1/4 throttle. What should I do now?
 

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Ride it - just don't flog it and don't ride for more than 20 minutes before letting it cool again - after that just ride normally
 

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So you used synthetic oil? You need that initial wear of the rings to the cylinder crosshatch. IDK at this point, i've not tried a break in with synthetic.

For the last two 400ex's I rebuilt, I started ran them varying the throttle from 20-50% until they reached temp then shut them down. I heat cycled twice, then took it out where I could run it. I then run it from 20-60% with lots of starts and stops (I like to let off the throttle, and use engine compression to slow the machine down, puts a different stress on the engine to help that initial wear). I do that for about 10 minutes, then another 10-15 minutes of 20-85% power starts and stops, then I change the oil. I do 4 hours after that running up to 90% power and another oil change.

After that I ride it like i stole it. I have two machines right now we finished the 4 hour run and are ready to hit the dunes, soon as this gawd-awful summer heat wave ends (still hitting 110 weekly here).

Probably hit the dunes again for labor day.

-DallanC
 

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Discussion Starter #17
Yea I wasn’t aware that I needed conventional at the time. So I’m thinking that I will now put some stress in the motor and ride if for about 20 minutes of 1/4-1/2 throttle cool then 1/2-3/4 cool then full go cool and then change. I already did one heat cycle, should I do another then get on it? Does this sound okay or should I change it up some?
 

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It depends on the engine construction, the engines purpose and how long you want it to last.

I know the 'proper' break-in procedure and what kind of oil to break-in with, but the break-in for my 70's Triumph air cooled with cast iron cylinders vertical twin is totally different than my 04 CRF250. I can put a new piston and rings in my CRF, not hone the cylinder (honing is not recommended for plated cylinders), fill with 15w50 synthetic oil on Sat., start the engine to check for leaks and proper coolant flow (never even reaching operating temperature) and then race it for 2 hours at upwards of 12,000 RPM and never worry about it. The old Triumph is filled with non-detergent 10w oil and idled for about 5 minutes, shut off and let cool so the head can be re-torqued - this is done 3 times before riding - first ride around town for about 20 minutes, let cool and re-torque the head before starting again - this is repeated until the head torque stabilizes. Change the oil and fill with 20w50 Castrol GTX. Then ride from town to town (5 to 10 miles one way) at about 45 MPH with varying engine speeds and upon return, let cool and check the head torque - two or three trips and then some cruising at highway speed up to 20 or 30 minutes one way - 4 or 5 trips and then if you get a wild hair, a burst up to 100+ after a 20 minute at highway speed. Proper break-in will assure long engine life.
 
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