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new head, new rings & combustion blow-by (Read 385 times)
deadman333
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new head, new rings & combustion blow-by
04/02/16 at 16:32:21
 
 I own a 2005 LS650.  I've started riding in July of 2016.  The bike had approx 6,000 miles on it.  Since i began riding it I have racked the mileage up to 33k and some change.  
   Recently I began to notice a loss of power after being on the bike for 20-40 miles.  Eventually I began to notice the loss of power within 20 miles of riding.  
 As it turns out the head was cracked right thru the threads where the spark plug threads in. After removing the head I could see the crack was quite extensive: moving upward from the spark plug and kind of wrapping the exhaust valve closest to the plug.  
 Since then i have completely tore down and rebuilt the upper engine:          
  1.Replaced the cracked head and head cover.
  2. Removed old rings & replaced with new.
  3. Replaced cylinder Jug gasket that sits between the upper and     lower parts of the engine.
  4. Replaced the head head gasket with a new one.
  5. Replaced Studs and Head bolts with new.
  6. Adjusted valves to .004in

 Upon rebuilding after replacing rings and cracked head all seemed to be in order.  The bike started right up & sounded great.  I tested compression pressure: It measured between 185-190psi.
 On the first ride everything seemed ok for the first 10-15 miles.  I was thinking that maybe i didn't have the power i expected, but thought that might be the case until the rings were broken in.  
 I stopped for gas approximately 10 miles into the ride.  No oil leaks, no smoke, and the bike seemed relatively cool.  
 I filled the bike up and continued on my test ride.  Some where around mile 15-20 I noticed my left boot was shining under the interstate sodium vapor lights.  
 I knew immediately it was oil and it was likely i had blown a gasket.  I was near a buddy's house and pulled off the interstate and into his driveway to inspect the engine for the source of the leaking oil.  the upper engine was clean.  There was no oil from the cylinder up to the top of the upper engine.  Of course i had just added oil upon completion of the repairs, and it appeared the leak was in fact coming from the oil cap.  
 I turned to tighten the cap and it was loose.  Maybe a half to three quarters turn.   So I added some oil to account for what had been lost and continued my ride to my girlfriends house where i intended to stay the night.  Approx fourteen miles.  
 Upon arriving at her house she opened the garage door and I rode the bike in to check it out under the lights.  It appeared that no more oil had been leaking since tightening the oil cap.  
 
The next morning I cleaned the leaky oil from the lower engine casing, made sure the oil cap was in fact tight, and headed for home- almost a forty mile trip.  
 Before i made it home, but on the last leg of the journey, I noticed my boot was shiny and covered in oil again.  
 I made it home and immediately inspected the bike.  I could see while the bike was running oil was oozing out in the front of the engine at the cylinder gasket.  No doubt it was the source.  
 
 I immediately ordered all new gaskets and studs and commenced to tearing the bike down and removing the engine.  
 I was ready for the gaskets when they arrived six days later and quickly but carefully put the bike back together.  Feeling confident that i was back in business a few days later I took the bike for a short test drive upon completion of putting it back together.  
  It was raining and i was late for a weekly gig i play across town so i loaded up my gear in the car and headed out.  Knowing i'd be late getting home and would have to rise early to leave for work the next day.  
  Early next morning I woke up a little late for work and was in a hurry to get on the road.  Of course the battery was just a hair too far drained to start the bike.  It turned over but wouldn't start.  Of course my short test run before my gig the night before was not enough to charge the battery so I jumped it off and headed for work approximately 18-20 mile trip-late.  
 Within five miles of work I had to stop on the interstate due to traffic.  When my left foot hit the ground it slid like it had oil on the bottom of my boot.  I looked down and of course it was covered in oil.  I carefully completed the ride to work and immediately inspect the engine for the source of the leak.  I saw that i still had enough oil in the bike to see it thru the oil inspection window, but it was obvious where the source of the leak was coming from.  
 It was the same darned cylinder gasket between the lower and upper engine, but this time the entire front side of the gasket was blown out and standing perpendicular to it's the front of the engine. It was standing straight out in the front of the engine and facing the front tire.  
   I think it is obvious that the engine is experiencing blow by upon compression and is pressurizing the lower end of the engine.  Thusly causing my cylinder gasket to blow out.  

My question is:  What are the possible ways that pressure from combustion can make it from the upper to the lower compartment of the engine?  and: What is the most likely cause from those possibilities?

Thank you.

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deadman333
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Re: new head, new rings & combustion blow-by
Reply #1 - 04/02/16 at 16:33:29
 
Correction:  I started riding in July 2014.
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justin_o_guy2
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Re: new head, new rings & combustion blow-by
Reply #2 - 04/02/16 at 16:38:56
 
Did I overlook the
I checked the rings end gap
I made sure that the piston to cylinder wall clearance was good
I cross hatched the cylinder
parts?

Footpeg bolts Must be tight, to close the case halves.
A cylinder can develop a ridge at the top, from the compression ring. Slapping a new one in and not cleaning that up can break the new ring.
Cylinders can develop a bit of a taper.

More to doing a top end than slapping parts in.
I'm hoping you did everything and just need to tighten the peg bolts up.
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Kris01
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Re: new head, new rings & combustion blow-by
Reply #3 - 04/02/16 at 19:56:16
 
Clymers lists compression at 145-203 psi with bare minimum being 116 psi. Sounds like the rings might be okay.
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Re: new head, new rings & combustion blow-by
Reply #4 - 04/03/16 at 03:50:15
 
You didn't happen to block the breather hose on the top of the rocker box by any chance? A fat rubber hose leading from rocker box to the airbox? If that's blocked, crankcase pressure will look for another way out and its conceivable that it chose to blow out the cylinder base gasket. Hope that's all it is. Check the new rocker box you bought has the steel wadding inside, and that it's not blocked solid with old gunk.
That's all I got.

Good effort racking up 25000 miles in 2 years  Cool. How's your timing chain?

Oh yeah: to answer your question about compression getting into the crank case:whenthe piston rises, it compresses in the cylinder. But when it falls, it also pressurises the crankcase. The pressure gets out through that hose. Good work btw.
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deadman333
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Re: new head, new rings & combustion blow-by
Reply #5 - 04/03/16 at 19:09:41
 
okay.  thank you for your response.  I am disassembling the bike currently to remove the upper  engine.  I did not know the lower end pressurized and escaped thru the vent.  Blockage there would make sense.  
 I hoisted the bike today to bring it to a comfortable level for working on it, and began disassembly to remove upper engine.  This afternoon i first cleaned the bike removing the oil from leakage that covered the lower end and frame of the bike,  removed the battery, battery case, Carburetor, and muffler/exhaust.  Tomorrow(monday) I will remove the engine from the bike and inspect the steel wadding and vent for blockage.  
 I agree that the rings are likely not the problem since combustion pressure test was so close to the high end as specs suggest.  
  Thanks again for the help.  I will return with what i find as soon as possible.  Hopefully tomorrow evening after work.  This leaves me with high hopes for a relatively easy solution that i had not considered.  
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deadman333
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Re: new head, new rings & combustion blow-by
Reply #6 - 04/03/16 at 19:17:10
 
  I did not check the ring gaps or measure cylinder or piston clearance.  i have purchased a digital micrometer and intend to do all of this.  I will post the results as I remove the upper engine and disassemble.  
   I should have done all of these things already but did not.  I have already considered after the fact that one of these factors is causing the problem.  
Thank you for your help from a novice wrench turning fool.  I will update you with measurements in a couple of days if not before.
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justin_o_guy2
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Re: new head, new rings & combustion blow-by
Reply #7 - 04/04/16 at 05:26:30
 
Someone said your compression is good.
If you have not checked the peg bolts, do.
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justin_o_guy2
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Re: new head, new rings & combustion blow-by
Reply #8 - 04/04/16 at 05:33:19
 
An inside diameter dial caliper will find if it's round or tapered.
I take my pistons and jugs to an engine builder. Yeah, costs a bit, but, I know it's right.
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deadman333
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Re: new head, new rings & combustion blow-by
Reply #9 - 04/04/16 at 06:33:08
 
Thank you.  I understand that compression is good.  That is why I included the info in the original post.   I have not checked the foot peg bolts because I took them off to remove the muffler in the process of removing the engine to replace the cylinder jug gasket that blew out.  
 I don't understand how foot peg bolts have anything to do with the cylinder gasket.  
 If I was having a problem with a gasket on the lower end I would understand how that could be a problem.  
   Gaskets arrive Wednesday.  I will have the upper engine removed today and take measurements of ring gaps, piston , and cylinder.
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Re: new head, new rings & combustion blow-by
Reply #10 - 04/04/16 at 16:42:48
 
deadman333 wrote on 04/03/16 at 19:17:10:

Thank you for your help from a novice wrench turning fool.


You're no fool. You're asking intelligent questions, providing the relevant information and acting on the advice you've received. You're doing the work yourself and learning from the experience. Keep up the good work, mate.
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gizzo
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Re: new head, new rings & combustion blow-by
Reply #11 - 04/04/16 at 16:58:47
 
BTW and just for interest's sake, your old cylinder head with the crack might be salvageable if you know a good welder/machinist engine builder. They can grind out the crack, weld it up and machine it back to shape. They'll have to fit new valve seats too. Worn cam tunnel can be fixed like this, too. Not cheap and probs not worth it in the 'states. You guys seem to have unlimited access to secondhand parts. But in australia, not so much. I've had maybe a dozen Honda RFVC head successfully reclaimed this way. Used to know a really good engine guy but then he died.
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Re: new head, new rings & combustion blow-by
Reply #12 - 04/04/16 at 18:41:18
 
I would be interested in knowing why the head cracked.

This is the first one I have ever heard of.

Was the bike overheated?
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gizzo
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Re: new head, new rings & combustion blow-by
Reply #13 - 04/04/16 at 19:15:15
 
Same. I only saw in on older Honda XR heads. they crack between the spark plug and valve seat. later models came with smaller valves and more meat between the plug and valves, as well as increased oil capacity and an oil cooler.
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justin_o_guy2
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Re: new head, new rings & combustion blow-by
Reply #14 - 04/05/16 at 05:42:19
 
I must have gotten it wrong. I thought you had a low engine leak.
I didn't notice how you put the head cover on the head.
What sealer you used.
Checking out that vent hose can't be a bad idea.
Just how much of a leak is it again?
I've seen major projects go sadly it awry, a Mack truck engine is dead today, and other smaller disasters. Add up all the wins and losses, I was brilliant. I quit that company with Zero notice and they called Me a few months later to work on a project, alone, after hours,,,, because they didn't know anyone else they could trust to work unsupervised. You walked in, you did stuff, and it's Running. Okay, maybe there were some unknown unknowns, and, maybe something didn't go just right,,but you're no dummy.
I do wish people could find this place before they get real adventurous.

And how Did that head get cracked?  That's a really good question.
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