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TDC old xt225 vs new xt225 lets solve this #151279 04/28/21 02:32 AM
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TXrider Offline OP
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Ok, I want to find the definitive answer to what the top dead center mark on the 2001-2007 xt225 engine is.

I know everyone will say the center mark or the last mark, Lol. That's ok, however if you can't provide official documentation it doesn't mean you are right or wrong, because "you've always done it that way or you've been rebuilding Yamahas for 40 years and its' always been" without the documentation it doesn't mean you are right or wrong either.

I will state may case. I have purchased the official Yamaha manual $89.95 and shipping 24.95 for the 2001-2007 XT225. It is the H version (1996) and the yamahapubs customer service says Yamaha confirms it's the correct manual for 2001-2007. Obviously that is not correct. The manual shows the T as TDC and even indicates it for the H model (1996) on the cover page and several parts referenced are different. I feel like I have paid for the right to know what the true TDC mark is, directly from Yamaha.

The new engine timing marks I--I I are 9 degrees apart. I know this because there are 40 teeth on the cam gear, 360/40 = 9, meaning 9° for every tooth. If the cam gear is TDC on the compression stroke and rotor is at the center mark and I move the chain 1 tooth the pointer will point to the next mark.

In the ignition timing check pg 3-17 it states the "accepted firing range" is between the two lines (on the old motor). Since there is no correct documentation for the new motor one can and has assumed that this is the case for the I--I marks. Since I know the new motor marks are 9° apart, if I use the far right mark that would place the "acceptable firing range 9 to 18° before TDC. This seems excessive to me and could possibly burn up the piston if not engine. If the timing is late it would account for the lack of power. This could be some of our engine inconsistency problems. I have read XT250 engine manual where firing should be 10° at 1450rpm.

If you have official documentation that matches the new engine marks, I'd love to see it. Yamaha says to take it to a local dealer, the local dealers won't divulge the information. I don't think they know for sure either. If I took the bike to the dealer would it be aligned correctly? I mean, they can't seem to put the right oil filter in the bike.

The new engine port frames the marks (I--I I). Does the old engine port frame the 3 marks?

We need several people to answer these questions to get the definitive answer.

1. People to go to their old engine with the T timing mark and look for the "acceptable firing range" marks on the rotor, Where are the marks? Are they before the T mark, if yes, does the T mark act as the third mark and does the port frame the three marks (I I AT) ?

2. People who have a new motor and you know it hasn't been apart before and can align the cam and rotor marks, which mark does the pointer align to on the rotor? Please take into consideration chain stretch. Mine engine has been apart before and the mark was a little behind the center mark from chain stretch.

3. Has anyone actually done the ignition timing check? What did you find?

I'm serious, Let's settle this.

Thank-you to each and everyone for their time and efforts.


Last edited by TXrider; 04/28/21 02:43 AM.
Re: TDC old xt225 vs new xt225 lets solve this [Re: TXrider] #151287 04/28/21 02:18 PM
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2wheelfun Offline
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Pull the plug out and feel where the TDC is, then you'll know which mark is right.

Re: TDC old xt225 vs new xt225 lets solve this [Re: 2wheelfun] #151297 04/28/21 10:19 PM
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Thanks. I've done that, can't distinguish TDC with a certain mark, they are too close together. That's not really what I'm asking for here.

Last edited by TXrider; 04/28/21 10:21 PM.
Re: TDC old xt225 vs new xt225 lets solve this [Re: TXrider] #151326 04/30/21 04:01 AM
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Well I think I have the answer. I put in a new timing chain, along with two new chain guides. I spec'd the cam gear and it's fine. I compared the two chains by hanging them on a screw driver making sure they sat the same. The old chain was about 3/16 longer than the new chain. I went ahead and installed the new chain. The cam mark and the rotor mark will now, only align with the case and head alignment marks when the third mark on the rotor is used. I spent extra time moving the chain one tooth on the cam both clockwise and counter clockwise and the all marks would only align with the third mark on the rotor. I will check ignition spark timing as soon as I can and report back.

Last edited by TXrider; 04/30/21 04:22 AM.
Re: TDC old xt225 vs new xt225 lets solve this [Re: TXrider] #152436 10/16/21 06:55 PM
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utahn Offline
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Thank you so much for this, I had the exact same question. There is no T on my flywheel.

It also kinda makes sense, spark timing will be early thus in the middle of the |---|.

Re: TDC old xt225 vs new xt225 lets solve this [Re: TXrider] #152438 10/16/21 08:56 PM
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Really interesting and useful information. Thanks for your efforts and posting your findings.

Can you tell us how many miles are on the old timing chain?

Many motorcycle mechanics text books recommend making up a probe type measuring tool that will screw into the spark plug tapping in the head and use that to determine TDC.

My two stroke bikes have a central spark plug tapping and I made up a dial indicator adapter which I use to find TDC.

Based on your experience, do you think such a set up could be used on an XT 225?

Re: TDC old xt225 vs new xt225 lets solve this [Re: TXrider] #152439 10/17/21 01:01 AM
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peejman Offline
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I'm curious why you're concerned with finding exactly TDC? The cam has some dwell on both sides of TDC, so there's no need to be super precise when checking/setting valves. Is there some other reason?


This shall pass, be still and know.
2006 XT225, UNI filter, ProTaper bars, MSR handguards, SS front brake line, Shinko 241's.
Re: TDC old xt225 vs new xt225 lets solve this [Re: TXrider] #152442 10/17/21 05:15 AM
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If this is just about setting the valves, it makes no difference where the marks are. As long as the valves are closed, which is pretty much anywhere during the compression/power strokes, you can set the valves. The engine does not have to be at TDC to set the valves.


The above is my opinion. Your mileage may vary.
1994/2001 custom built XT225 with a ton of aftermarket parts.



Re: TDC old xt225 vs new xt225 lets solve this [Re: TXrider] #152450 10/18/21 08:01 PM
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I think TXrider is concerned about valve timing, not setting the clearances. A worn and stretched timing chain might have some effect on that.

Considering his last post was April 30, 2021, we may never know.

Re: TDC old xt225 vs new xt225 lets solve this [Re: Pumpguy] #152451 10/19/21 11:49 AM
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peejman Offline
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Originally Posted by Pumpguy
I think TXrider is concerned about valve timing, not setting the clearances. A worn and stretched timing chain might have some effect on that.

Considering his last post was April 30, 2021, we may never know.


Perhaps that's true, but valve timing isn't adjustable. You get what you get with the parts you've got. I don't remember how many teeth are on the cam sprocket, but being off 1 tooth is a huge change and will likely result in an engine that doesn't run or is very, very unhappy. If you had lots of spares, you could degree cams and pick the one you like the best.


This shall pass, be still and know.
2006 XT225, UNI filter, ProTaper bars, MSR handguards, SS front brake line, Shinko 241's.

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