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hedpi

400?..426?..differences?

11 posts in this topic

So i bought a used YZ...thing is it says on the papers it is a 99 yz400, but on the head it says 426...

The prev. owner doesn't know "anything" about the bike, he already bought it like that, and didn't do any major engine maintenance during the time he had it, only oil change valve adjust etc..

Recently the valves were at the max of the adjustment (120 125 shims) so i had the valve seats done, new valves, etc etc. After that, the bike started to make an obnoxious noise, which i thought was from poor valve adjustment.

This is what i've tried:

- Valves were set (in milimeters) at E30 E30 I20 I20 I20.. first thing was trying to put then tighter (as the valve clearance is E25-30 and I15-20. That didn't work.

- Valves were set per 426 clearance (from the manual in motoman's website). That didn't work either.

- Couterbalancer key was checked and it was tight, no lash.

- Various timing settings.. some actually were noisier than others...

Which leads me to some questions...

Is the timing from the 99 400 equal to the 2000 426?

The old valves were stainless so i think it was a 2000 head.. but it could be a 2001+ with stainless valves (because theyre cheaper?..i don't know.. but i have to think of all the possibilities). If so, is the timing equal to those?

I tried setting the timing per the dots, per the lobes, counting 12 links, counting 14 links... and +1/-1 of each of those.. the lobes method seems (as i've read) to be the most acurate, but it didn't work also, supernoisy....

I'm fed up with trying stuff with no result..i have had the bike apart for like a month now.. or more.. i dont even remember.. what should i do?

Thanks for the help :ride:

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99 is a YZ400. Each year from 98-present the 4xx bikes have a large list of changes to them. Each year being better than the previous.

For the timing, get the TDC mark on the flywheel. Easiest way to check this is put a pick down the plug hole and find TDC off that, then check the mark on the flywheel. Maybe you sheared a woodruff key. Then 12 pins between the cams, marks horizontal with the head.

There could be some many issues with the bike. Check the basics - spark, compression and fuel.

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yeah i used a screwdriver to find TDC and it was 100% aligned with the "I" mark.

then i tried the 12pins and horizontal marks, and it did not stop the noise.. :ride:

You think the spark compression or fuel could have something to do with it? Wouldn't the bike run bad like that? I've tried running her once to see how it felt, and it didnt seem to lack power.. :ride:

thanks for the reply

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Did you re-use the old cam chain or use a new one when you got the head work done?

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It sounds like your motor was converted to a 426. I forgot all the parts but I think its just a swap of the cylinder, head, rod, and piston, maybe the crank too. Do a search and you should be able to find that information

The 426 uses titanium valves and I dont thin the 400 does. So what valves did you buy, 400 or 426? I really dont know if it matters, but they could be different.

Make sure your chain tensioner is working right, or buy a manual one and replace the chain.

How much noise is coming from the top end? My 426 rattles and clanks pretty noisy

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Well i bought the ss valves, because it had ss valves in there before, and it wasnt noisy! well it was noisy, but not like this..

i think the tensioner is ok, cause when it is "activated"/"unscrewed"/whatever, the chain is stretched..the guys at the shop that did the seat work say it's not caused by the chain but i dont know..

yeah it seems to come from the valves, and its a little bit more audible on the right side than on the left side.. but very very audible on both..

yeah the bike is noisy, but it wasn't this bad, it was just normal valve noise.. now it's so noisy that everyone turns their head to see where is the "ducati"..lol :ride:

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If the chain is stretched, it might be a good idea to replace it. My buddy just blew up his 400 to 426 conversion motor because the guy he bought it from reused the 400's chain.

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have you checked your oil flow to the top end? Also check the carb closely.

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The cam chain is supposed to be replaced every 40 hours...many people overlook this and this is a very common problem. But what do i know....i ride a pinger

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