What happens if you don't shim your valves

[Potentialbuyer2000]

I have a feeling my valves are out of adjustment (hard starting and 110psi compression). I dont feel like messing with them at the moment, will this damage anything?

Bike is a 2003 yz250f

Edited October 3, 2020 by Potentialbuyer2000

[BPPerformance]

If you can get it started it will be fine - those usually have intake valves that get too tight and you will lose compression and start hard especially when hot.

[Potentialbuyer2000]

1 minute ago, BPPerformance said:

If you can get it started it will be fine - those usually have intake valves that get too tight and you will lose compression and start hard especially when hot.

Thanks for the fast response. It starts hard when cold but usually starts fairly easy when it's hot, but sometimes not. Plan on using it for the rest of this year and fixing it over the winter.

[Trailryder42]

What now may be a simple valve shimming job to get the clearances in spec, can turn into valves wearing into the seat enough to need a valve job, cutting and lapping sort of work. If the clearances are gone, that kind of wear has started.

Edited October 3, 2020 by Trailryder42

[piltoyougram]

When you stop for a break make sure you park on a hill so you can bump start. The problem won't go away and will continue to get worse on the starting deal. Other wise ride! 

[SlowDinoDog]

That's what my CRF450X did with a badly worn intake....its hard to start COLD.

It would run and idle warm...I was eventually down to the thinnist shim.

It got to the point of not starting and idling cold.

The shop said the edge of my intakes were so sharp he could shave with them.

Edited October 3, 2020 by SlowDinoDog

[Potentialbuyer2000]

2 hours ago, BPPerformance said:

If you can get it started it will be fine - those usually have intake valves that get too tight and you will lose compression and start hard especially when hot.

Thanks for all the quick responses. Ive done a little more research and from what ive heard, once you start shiming the valves they'll only get worse and worse. is that true in most cases or is it possible i can shim them and itll be fixed for a good amount of time? (ive heard it may only last 5 rides before they go bad again). Is it possible I need new valves? If so how much would it cost for a shop to do them? I could probably do it myself but I dont have the time to do it. I do see evidence of the head being off so I wonder if the valves have been done before and it does just need a good adjustment?

My bike starts hard cold but will idle no matter the temperature of the motor and works good. It sometimes will start relatively easily as long as i give it 3 small kicks and one big one at TDC.  It does make little pops on deceleration, but I think that may just be because its running a tad lean.

[Tony Wyp]

3 hours ago, Potentialbuyer2000 said:

I have a feeling my valves are out of adjustment (hard starting and 110psi compression). I dont feel like messing with them at the moment, will this damage anything?

Bike is a 2003 yz250f

It will damage your wallet very soon.

[Tony Wyp]

7 minutes ago, Potentialbuyer2000 said:

Thanks for all the quick responses. Ive done a little more research and from what ive heard, once you start shiming the valves they'll only get worse and worse. is that true in most cases or is it possible i can shim them and itll be fixed for a good amount of time? (ive heard it may only last 5 rides before they go bad again). Is it possible I need new valves? If so how much would it cost for a shop to do them? I could probably do it myself but I dont have the time to do it. I do see evidence of the head being off so I wonder if the valves have been done before and it does just need a good adjustment?

My bike starts hard cold but will idle no matter the temperature of the motor and works good. It sometimes will start relatively easily as long as i give it 3 small kicks and one big one at TDC.  It does make little pops on deceleration, but I think that may just be because its running a tad lean.

Shimming valves makes them last and is the correct thing to do as normal maintenance.

You will find how bad the wear is when you select the thickness of your shim. You may be right in clearances not lasting, if the wear is great.

Edited October 3, 2020 by Tony Wyp

[SlowDinoDog]

33 minutes ago, Potentialbuyer2000 said:

Thanks for all the quick responses. Ive done a little more research and from what ive heard, once you start shiming the valves they'll only get worse and worse. is that true in most cases or is it possible i can shim them and itll be fixed for a good amount of time? (ive heard it may only last 5 rides before they go bad again). Is it possible I need new valves? If so how much would it cost for a shop to do them? I could probably do it myself but I dont have the time to do it. I do see evidence of the head being off so I wonder if the valves have been done before and it does just need a good adjustment?

My bike starts hard cold but will idle no matter the temperature of the motor and works good. It sometimes will start relatively easily as long as i give it 3 small kicks and one big one at TDC.  It does make little pops on deceleration, but I think that may just be because its running a tad lean.

I was getting about 10-15 hrs of riding on each shim job....before I could notice it was getting hard to start again...I think I remember a bit of backfiring.

I probably shimmed mine about 3 times...until I was down to using the thinnist shims in the kit.

Once the Ti valves start wearing...they wear quickly.

You'll need to pull the head eventually, and have it rebuilt with new valves.

[SlowDinoDog]

You can pull off the seat and tank...pull the valve cover...and measure your clearances with skinny feeler gauges.

Edited October 3, 2020 by SlowDinoDog

[Potentialbuyer2000]

4 minutes ago, SlowDinoDog said:

You can pull off the seat and tank...pull the valve cover...and measure your clearances.

I already have the bike all apart so pulling the valve cover is easy. Going to canadian tire to buy the proper feeler guages in a hour or so and will check the clearances when I get back so I know what im getting into.

Do you remember how much it was for the shop to do your valves SlowDinoDog?

Edited October 3, 2020 by Potentialbuyer2000

[SlowDinoDog]

2 minutes ago, Potentialbuyer2000 said:

I already have the bike all apart so pulling the valve cover is easy. Going to canadian tire to buy the proper feeler guages in a hour or so and will check the clearances when I get back so I know what im getting into.

for sure, buy the right feeler gauges. Take your time. Make several measurements to make sure you're correct. Just saying its a little difficult to be precise the first time.

Edited October 3, 2020 by SlowDinoDog

[RichieGoatGruff]

7 hours ago, SlowDinoDog said:

I was getting about 10-15 hrs of riding on each shim job....before I could notice it was getting hard to start again...I think I remember a bit of backfiring.

I probably shimmed mine about 3 times...until I was down to using the thinnist shims in the kit.

Once the Ti valves start wearing...they wear quickly.

You'll need to pull the head eventually, and have it rebuilt with new valves.

The 4 valve Hondas are harder on the valves than the 5 valve Yamahas...

[SlowDinoDog]

39 minutes ago, RichieGoatGruff said:

The 4 valve Hondas are harder on the valves than the 5 valve Yamahas...

That has been my experience too....with mine... and the friends I ride with...seems the 450s go first before the 250s for off-road riding. 

It may be a temperature thing and the largest diameter valve may have the hottest edge.

Edited October 3, 2020 by SlowDinoDog

[RichieGoatGruff]

30 minutes ago, SlowDinoDog said:

That has been my experience too....with mine... and the friends I ride with...seems the 450s go first before the 250s for off-road riding. 

It may be a temperature thing and the largest diameter valve may have the hottest edge.

Honda has to run a more aggressive cam to achieve similar flow rates on the intakes, may be one reason... Or, better intake flow makes for a cooler chamber.

[Potentialbuyer2000]

Sorry didnt get a chance to check the valves last night but I checked them today and they ARE in spec, guess i wont be needing to pull the head apart anytime soon. I dont have the right width of feeler guage but I made it work. Will order the proper one next time I make an order on fortnine and will check them mid season next year. I did find proof that someone has had their hands in this motor before (marks on nuts and bolts there shouldn't be, things like that) and I Changed the spark plug and put a camera down the hole and there is next to no carbon buildup on the piston, definitely was rebuilt within the past couple of years, i guess it's an 03, probably should've expected that. Just hope someone put new valves in it when they rebuilt it, which they probably did.

As for the Hondas valves I've heard bad about them and that's one of the reasons I stayed away from them even though its my nearest dealer (yami dealer is another 30 mins away).  Just wanted to see how ture that was.

Thanks for everyone's help 

[shrubitup]

57 minutes ago, Potentialbuyer2000 said:

Sorry didnt get a chance to check the valves last night but I checked them today and they ARE in spec, guess i wont be needing to pull the head apart anytime soon. I dont have the right width of feeler guage but I made it work. Will order the proper one next time I make an order on fortnine and will check them mid season next year. I did find proof that someone has had their hands in this motor before (marks on nuts and bolts there shouldn't be, things like that) and I Changed the spark plug and put a camera down the hole and there is next to no carbon buildup on the piston, definitely was rebuilt within the past couple of years, i guess it's an 03, probably should've expected that. Just hope someone put new valves in it when they rebuilt it, which they probably did.

As for the Hondas valves I've heard bad about them and that's one of the reasons I stayed away from them even though its my nearest dealer (yami dealer is another 30 mins away).  Just wanted to see how ture that was.

Thanks for everyone's help 

Still need to address the 110 PSI and you already know it's not the valve clearance so top end time.

[Potentialbuyer2000]

I have a feeling that the low compression is due to the decompression system and that im jot holding the it WOT. did a compression test on my atv and it only made 125 psi before I held it WOT while cranking, then it made 155. When I get my new throttle cable I will try again, also bike is torn apart and front tire is off to replace bearings and brake pads so its kind of hard to give it a proper kick while its on 2 blocks of wood, sketchy.

[ohiodrz400sm]

I had a brand new 03 back in the day.  As you said, there is an automatic decompression mechanism on the exhaust cam and you need to hold it WOT when testing.   It's been a long time, but I don't remember the bike being particularly difficult it kick, so I would except a fairly low reading.  I don't know if Yamaha even publishes a value.  1engine I'm extremely familiar with (drz/ltz400) has a similar compression ratio, auto decomp and factory recommendation of 135 PSI with the decomp active. 110 psi with a working decompression system and closed throttle probably isn't that far off from normal. However, that is just speculation as I never did a compression test on my 03.

On the subject of valves, running it with a zeroed out valve would damage the valve and seat.  Another bit of misunderstanding is valves don't wear in a linear progression.  They require shimming because the faces are worn/damaged. If reshimming becomes regular maintenance like adjusting a chain or changing the oil, the valves really should be replaced. To continue to shim only increases the possibility of catastrophic failure. The gentleman that mentioned his valves were worn to a razo'rs edge was extremely lucky a valve didn't break and destroy the entire engine.

I don't know if I would assume anything about what the previous owner did in regards to replacing the valves. You have 2 choices, be proactive and have the head rebuilt or run it and and keep an eye on the clearance. If you find they are continually moving, then you should have the seats recut and the valves replaced.