crf150 seized.

[Timmay#678]

Hi, a kid with a 150 asked me to have a look at his bike after it locked up on him. I'm more of a 2stroke man and have done plenty of top end and bottem end rebuilds on them but never opened a 4stroke before (those yzfs just dont give any trouble :cool: ).

Anyways, after pulling off the head, the valves have certainly met the piston a few times before the bike seized, there are clear marks on the 2 exhaust valve and one of the intake valves. also one of the lifters has broke the camshaft holder, and the camshaft lobe above that valve has been deformed a good bit. Other than that everything looks good, piston and barrel are good and rod isnt bent or anything. Seems like the kid got off very lightely!!!

The valves dont seem to be bent or anything, but when you rotate the cam around, at one point the inlet and exhaust valves are definatly both open (only a small bit though) at the same time, which I dont think is right, as i thought the valve opening didnt overlap. I'm thinking that I'll escape with just new valves, camshaft, camshaft holder and lifters. However i've never installed valves before, and am not too sure about the whole process.

Am I better off leaving it all to a proper bike mechanic?



I'm not really sure of what caused the valves to hit the piston in the 1st place also! the bike was a little low on coolant and oil, it was the kids 1st 4stroke bike and i dont think he did much maintaince on it. Having said that he couldnt have rode the bike for more than 4/5hours after buying it before this happened! the timing chain was well tensioned, yourman is a beginner rider and I'd be very surprised if he managed to float the valves. Also the bike was starting grand before this happened, so I'd be surprised if the valve clearance had gone.

 

[Patman]

Seems curious that the valves would have marks but the softer piston would not.

From the sound of the damage I would guess he had it singing pretty high in the RPM range! Perhaps the valve clearences were tightened up a bit also?

 

[_JOE_]

Seems curious that the valves would have marks but the softer piston would not.

From the sould of the damage I would guess he had it singing pretty high in the RPM range! Perhaps the valve clearences were tightened up a bit also?

Yes, it does.





It would be foolish not to replace the piston.

Is this a 150 F or R?

 

[Rich Rohrich]

when you rotate the cam around, at one point the inlet and exhaust valves are definatly both open (only a small bit though) at the same time, which I dont think is right, as i thought the valve opening didnt overlap.

Am I better off leaving it all to a proper bike mechanic?

If you don't know that all four-strokes have valve overlap, maybe having someone with more experience on these engines look at it would be wise.

The 150R engine has a redline over 14,000 rpm, so guessing on the damage done this time could put the rider at risk down the line.

 

[Timmay#678]

:) , Thanks Rich for spelling it out for me!

Yes its a crf150R. There are some marks on the piston from the valves, I'm going to drop in a new piston kit definately while the head is off.

The kid is a beginner when it comes to mx, and any time I saw him on a proper track he certainly wasn't reving the bike hard then, but it locked up on him when he was out on the opened and he could well have had it singing for a while then.

I guess I'll drop the head into my local bike mechanic and let him take it from here before I muck up thinks, the kid wont be happy if it blows up on him again. I think I'll try and convince him that an 85 or 125 if hes big enough is a better bike for him!!!!

 

[SHSPVR]

Timmay#678 can post picture of this?.

 

[Patman]

the bike was a little low on coolant and oil, it was the kids 1st 4stroke bike and i dont think he did much maintaince on it.

Might be a key indicator.

 

[SHSPVR]

Might be a key indicator.

How low was the oil level?.
That possable Patman but there is one other thing that can cases the valve to hit the piston which has to do with the cam the way Honda made the cam gear holder which is a press fit design which has no key way or pin to keep it lock in to places from what I hear and I heard that some poeple had welded there to keep it from shifing out of line mint.
Cause by the fact that there not pulling in the cluch before hitting the rear brake lock up the rear wheel.

 

[Timmay#678]

Piston:


Valves:


Cam holder:


Camshaft:


I got about 500ml of coolant out of it, and about 300ml of oil from the engine (which is ment to be about 500ml)

 

[Patman]

Sure looks like more than 4-5 hours of a newbie rider to me.

 

[IndyMX]

Sure looks like more than 4-5 hours of a newbie rider to me.

No doubt.. That piston looks worse than the piston I pulled out of my 450 when I got it. And the guy I bought it from claimed to never have had the head off, in 4 years!

 

[SHSPVR]

Yup he cook the top end I can see it this what happ when let the oil level get to low

(which is ment to be about 500ml)

It should be more like 560ml or with oil filter change 587ml
coolant should be round 760ml
My guest to why the Valve where hitting the top of piston is that the valve where stick due lack of oil in valve guide so there for the piston push them close.
I would have them check the valve guide and even replace the valve seals

If need help with reinstall best take look at HotCan web site and there Video on doing the Valve and you will need a shim kit from Hot cam

 

[IndyMX]

Yup he cook the top end I can see it this what happ when let the oil level get to low


It should be more like 560ml or with oil filter change 587ml
coolant should be round 760ml
My guest to why the Valve where hitting the top of piston is that the valve where stick due lack of oil in valve guide so there for the piston push them close.
I would have them check the valve guide and even replace the valve seals

If need help with reinstall best take look at HotCan web and there Video on doing the Valve you will need a shim kit from Hot cam

Anyone have a decoder ring for this mess?

 

[SHSPVR]

Anyone have a decoder ring for this mess?

What do mean by that? I take it you are ref to my spelling and grammer.
I trying best fix it but web site wasn't work when I made the post.

 

[flyingfuzzball]

hmm the website wasnt work?

just say that to yourself a few times...

but yeah i was thinking the same thing when i saw that piston. Looks about 10 times worse then my 150R that had about 30 hours on it.

 

[Patman]

Might want to educate this kid that the CRF150R is NOT a CRF150F so it will need to have maintenance just like a 2 stroke race bike and not a run until all the stars in the galaxy burn out XR/CRF-F. I'm sure the final tab in parts and labor will sort of help point that out but a good swift kick in the pants can't hurt.

 

[IndyMX]

but a good swift kick in the pants can't hurt.

I was thinking that would be good just for general purposes for most "kids"..

 

[Rich Rohrich]

New riders often downshift and use the engine to slow down. If you down shift far enough with enough load on the rear wheel, it's easy to have the rear wheel drive the engine way past the redline. When the engine is being driven by the rear wheel, the rev limiter can't stop it from revving sky high. Rev it high enough this way and the valves will float.

When you float the valves they don't seat when they should, which effectively retards the cam timing.

The piston chases the exhaust valve closed near TDC and if the exhaust valve doesn't get settled on the valve seat in time you end up with the exhaust valve closer than normal near TDC and they'll hit the piston. A sure sign that an engine is being over-revved and floating the valves is bent exhaust valves. Patman's son did the same thing on his hot rod XR95. Patman explained what was happening to him and it was never an issue again.

A bit of rider education might be in order once the engine is repaired, so the kid doesn't have this problem in the future.

The 150R is an incredibly well made and stout little engine, but like anything, if you abuse it from lack of maintenance (even inadvertently while riding) , you'll break it.

 

[Rich Rohrich]

Yup he cook the top end I can see it this what happ when let the oil level get to low

The cam has a black coating from the factory. :coocoo:

 

[SHSPVR]

The cam has a black coating from the factory. :coocoo:

Look at Lube in his picture see the blue tint that mean getting hot and lack of oil in all my year of doing cam swap and rebuilds the only ones I have ever seem with black lode is due to lack oil
And Mine not black at all

 

[Rich Rohrich]

in all my year of doing cam swap and rebuilds the only ones I have ever seem with black lode is due to lack oil

You need to get out more. :)

Here's a picture of an OEM CRF150R cam from a brand new engine I just pulled apart.

Most of the Hot Cams also come with a black coating as standard. It's pretty common these days, at least here on earth. ;)

 

[SHSPVR]

Ok that good to know

 

[_JOE_]

Educate us Rich, what do they coat the cam with and what benefit does it provide?

 

[Timmay#678]

Thanks for all the replies people! I've chased up the history on this bike a bit more, the kid who owns the bike now bought it off a friend of mine, conor, whos little brother used it for 5/6hrs total, and it wasn't rebuilt by him (which i thought it was). Conor bought it off a very quick young rider, who won several races on it in the top level of the british youths championship, so no doubt the bike had a hard enough life. Conor had been told when he bought it that it had just been rebuilt, with a new piston and timing chain put in :blah: , I dont see how his brother and the kid who owns it now could have left such a buildup of carbon on a piston in the space of 10hours!

Also, the orginal owner had the head tuned, by a local engine rebuilder in Northern Irleand, which you can see in the inlet ports, in the photo below. There also appears to be a hairline crack running along the bridge between the two inlet valves. The crack is visable for about 2cm, it is hard to tell how how deep into the head it goes though!

Inlet port:


Exhaust port:

 

[Patman]

Come on Joe everybody knows the flat black coating is stealth paint like they put on jets and subs. ;)