Jump to content

Top end damage. Cause?

Recommended Posts

I picked up the RB cheap.  It wouldn't start (kick or pull start) even though it had spark and fuel.  I started digging into the top end and found this.  What do you think caused this?

Thanks for your help

-gd

IMG_20170326_170546377.jpg

IMG_20170326_180520537.jpg

IMG_20170326_202306719.jpg

Share this post


Link to post
Share on other sites
1 hour ago, o313 said:

Cam chain skipped?

tensioner condition?

valves adjusted?

octane booster in the fuel?

Intake valves were tight but not at 0.0.  Exhaust were in spec.

Tensioner seemed ok.  PO could have installed the cam chain off a tooth I guess.  I should have checked.  

The rings on the exhaust side of the piston is just from carbon buildup?  Any idea if that is a stock piston?

-thanks

 

 

Share this post


Link to post
Share on other sites

Well that's an interesting one! First off, yes, that is a stock piston. At a quick glance you might say, duh ...  the valves hit the piston and go with a timing problem. If I'm looking at it correctly, the obvious contact spots with the piston is on both of the exhaust valves but there are also minor signs of contact with the right intake valve which is the same cam lob that is toast and which broke the cam bucket and holder. The piston isn't showing any clearance issues with the squish clearance or the left intake valve. 

I'd be suspect of the valve springs in that engine. I think your exhaust valves were floating which is what caused the piston to exhaust valve contact as the piston caught up to the floating exhaust valves. 

As to the right intake, valve float usually won't cause contact because the piston is moving away. That is most likely a valve timing problem. Have you tried pulling that valve out yet? I'd imagine it's bent pretty good to blow out the side of the bucket like it did. The stock cams in the 150r are known for rotating over time and throwing the valve timing off which could cause that damage on the intake side. 

Share this post


Link to post
Share on other sites

Rollers move freely.  I'm waiting for a valve spring tool to come in the mail and then I'll be able to see if the valves are bent.

Share this post


Link to post
Share on other sites

It is a good thing you got it cheap.

I would toss all the valves and springs, they are relatively cheap for oem.  The crank bearing will probably fail, too, from impact stress.  The last engine I did top and bottom end with all valves and springs was (All OEM) $600.  You need the cam, tappet, and bracket, too, and don't assume the valve seats are good. 

Are you sitting down?  You are probably pushing $900 if the head does not need work.  A new head is $280, I just bought one, cheaper than installing new seats. 

I'm not one to part out bikes, but dang!

Share this post


Link to post
Share on other sites

The same thing just happened to me... and I think it was lack of lubrication.  The engine oil transferred to the tranny through a bad seal, and the valve spring tension galled the bucket when it lost oil.  Downward spiral from there, breaking the camshaft holder and the valve off at the retainer.  The good thing is that my PC cam survived, yours probably ran longer.  It was a new head in a new rebuild with 5 hours on it, so I am reusing the springs with one new valve.  But still need a lot of parts.

Share this post


Link to post
Share on other sites
On 5/2/2017 at 6:13 PM, gsa102 said:

The engine oil transferred to the tranny through a bad seal...

Which part is responsible for keeping the oils separate?

Share this post


Link to post
Share on other sites

Engine oil migrating to the gearbox is a somewhat common problem with other Honda separate sumps engines (CRF250R & X)

I've never experienced it on both CRF I maintain but the only place for oil to weep past is the RH crank oil seal. (engine side oil is pressurized, gearbox isn't)

In the case of a 2-stroke engine, in the event of a bad seal it's the gearbox lube that gets sucked into the crankcase due to the vacuum.

Share this post


Link to post
Share on other sites

Interestingly enough, I just had the opposite problem happen on my sons. It was a crank seal on the right side.

This thing is driving me nuts.

Share this post


Link to post
Share on other sites

After working on this awhile and thinking about it, I think the bucket seized in the holder and broke it when it lost oil.  My holder bore looks like it was sandblasted.  The oil can get into the tranny through the right crank seal or through the balancer seal behind the flywheel.  Both are serviceable without splitting the cases.

Check your oil before riding!  When we tested it after we found the issue, it lost about 50cc in 30 min.  Unless you are on an all day ride, you should catch it before this happens.

Share this post


Link to post
Share on other sites
On 4/3/2017 at 1:46 PM, gsa102 said:

It is a good thing you got it cheap....

 

Motor ended up costing me about $500 (including local shop grinding the seats).  I shopped hard for the best prices (ebay, HondaEast, Partzilla).

OEM piston, crank, valve seals, cam holder and valve bucket
Wiseco cam and stainless valves

I started it up the other day and it sounds good and tight.  :thumbsup:

Share this post


Link to post
Share on other sites

I have never ridden a 150R before and I didn't get a chance to ride this bike when i bought it (near basket case) so I can't really compare it to anything.  I am currently trying to get the AP to work cleanly and have many carb parts on their way.  When I took it for a test run around the almond orchard the power curve seem to feel more of a mid range emphasis.  I didn't rev it out fully either since it only have about 7 minutes of run time.  I remember reading that this cam is more of a mid range vs. the stock one which is more of a top end rever (from what I hear).  I didn't seem to have an abundance of low end but I normally ride a 14' crf250.  Maybe adding a tooth or two would help (stock RB gearing and I weigh 150lbs).

Share this post


Link to post
Share on other sites

Still transferring oil after a total split and rebuild with all new bearings and seals.  Took it apart to insect the crank seal, and saw grooves where the seal rides on the balancer drive gear.  Hopefully replacing the gear will cure it.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:


×