Author Topic: Who wants to guess what broke in my second engine? (Read 2601 times)

camelman · « **on:** July 11, 2011, 10:30:27 PM »

So, I recently tore a couple gears up on my 350F on the highway at a real 80MPH. It was pretty scary, but I was actually able to ride it home since the broken pieces just fell into the oil sump and stopped making noise.

Fast forward one week, and I'm installing an engine I bought from a friend. I actually rebuilt the engine (fresh bores with new pistons/rings/circlips, new seals, replaced a few transmission bearings, and I installed a cylinder head from my working engine that ate it's transmission), and I know it was done right.
However, it was left to sit in his father's garage without spark plugs in the holes while his father did a lot of wood work. I pulled the head off to swap on my ported head, and saw a bunch of gunk in the cylinders. It was all sawdust, as far as I could tell, so I just wiped it out as best I could and bolted the engine back up. I got about 200 miles of great operation out of the engine before it just went kaput. I have spark, and it is timed correctly. I put in new plugs, pulled the carbs and checked them, and finally pulled a plug and put my finger on the hole. It just doesn't seem to have much compression (I don't have an adapter that fits these tiny holes). Also, the oil light comes on until I crank it a few times, after which it goes off.

So, who wants to guess what's wrong with my engine?

Let the votes begin!

Camelman

scottly · « **Reply #1 on:** July 11, 2011, 10:54:10 PM »

I voted too-tight valves....

dave500 · « **Reply #2 on:** July 12, 2011, 12:20:01 AM »

define kaput?

Hush · « **Reply #3 on:** July 12, 2011, 12:53:06 AM »

Was that House hold Cavalry or Lancers?

camelman · « **Reply #4 on:** July 12, 2011, 07:25:33 AM »

Quote from: Hush on July 12, 2011, 12:53:06 AM

Was that House hold Cavalry or Lancers?

Please elaborate... this might be the answer I am looking for.

camelman · « **Reply #5 on:** July 12, 2011, 07:30:35 AM »

Quote from: dave500 on July 12, 2011, 12:20:01 AM

define kaput?

The bike pulled strong right off the bat, although it had a somewhat regular skip. I just figured it was my crappy daichi points, so I didn't worry about it.
On the highway, it had a couple throttle positions where it felt like the mixture was off. The cylinder head, carbs, and exhaust were the same on the prior engine, so I tacked it up to crud from float bowls getting into the emulsifier tubes while I had the carbs laying on the ground during the engine swap, although I didn't find any when I took the carbs off after the engine went kaput.
Things went bad after I rode to a friend's house and let it cool down. When I got back on the bike, it started right up, but was low on power, which quickly went away until I only had a handful of HP left. I don't know if all cylinders were firing, but throttle response was almost non-existent and it felt like the timing was radically retarded. I was able to ride it home, but only very slowly.

I'm pulling the head this weekend, so I'll have an answer soon.

Camelman

lone*X · « **Reply #6 on:** July 12, 2011, 09:10:09 AM »

A little saw dust should have blown out/burned out without doing any appreciable damage. When you pulled the plugs what did they look like? Mixture problem? Burned valves/holed piston?

camelman · « **Reply #7 on:** July 12, 2011, 10:16:21 AM »

Good question. The plugs were physically in good shape without excessive wear or damage. There was a little carbon build up that flaked off, but all were consistent and all had a mix of black and tan coloring. I don't think the mixture was off at all since the only thing that changed on the setup was the trans and new cylinders/pistons that were second over from stock.

I did notice that the exhaust puffed white smoke when I opened the throttle past 1/4 turn. It was a little oily smelling, but mostly just smelled like unburned fuel. It was only really visible in my garage whether the engine was started from cold, or had been ridden for an hour.

Hush · « **Reply #8 on:** July 12, 2011, 12:04:00 PM »

Being green is a good thing Camelman but trying to burn wood chips is just being cheap!
I mean I can see you stuffing the tank full of saw dust but how the Hell you gonna vacuum sync the carbs?
Then there is the problem of ignition, small pilot fires in each cylinder to fire the wood chips.
Nah it's just too hard man, go back to petrol or try running water.

dave500 · « **Reply #9 on:** July 12, 2011, 01:30:43 PM »

i got rid of our steam powered computer ages ago,i got sick of having to shovel in extra coal to do a complex calculation or run a dvd,you might have just fouled plugs?if you holed a piston youll have heaps of blow by out of the breather pipe,even with brocken rings i think youll have a plume of smoke,i wouldnt tear it down yet,try new plugs,some left over gunk might just have worked up and fouled them?

camelman · « **Reply #10 on:** July 12, 2011, 03:08:20 PM »

It sounds like wood chips and steam are both bad options for these engines. There are a lot of dogs in my neighborhood though. Maybe I should switch fuels?

I put new plugs in without any improvement. the engine isn't burning oil noticeably either. This is quite the mystery, but I'm leaning towards burned valves.

camelman · « **Reply #11 on:** July 13, 2011, 07:27:59 PM »

Well, the plot thickens. I checked the valve clearances on #4, and they were good. I checked the timing and spark again, and everything checks out. When I tried to start the bike, only #1 would fire. So, I pulled the plug on #4 and found that there is almost no compression. It seems that #1 is the only cylinder with a good enough seal to pull air in through the carb with enough force to pull fuel into the cylinder. The other three spark plugs were bone dry when I checked them after cranking the engine twenty or thirty times.

Argh! It looks like the head is coming off.

Grabcon · « **Reply #12 on:** July 13, 2011, 07:53:59 PM »

Before pulling the head put a little oil in each cylinder just prior to the compression check. The oil is meant to seal not to fill the cylinder. Something like a 1/2 a teaspoon. A syringe works well with out making a mess. Make sure the throttle is full open when doing the compression check. Use the electric start if possible. If you get a change in compression the rings are the likely culprit.

I know in this thread you said that it was running, but I would also check the valve timing. It is unlikely to have little or no compression on 3 cylinders.

camelman · « **Reply #13 on:** July 13, 2011, 08:07:40 PM »

Good point. I'll give it a shot before I pull it apart. It is a fresh bore though, so I doubt it is the rings. I did notice that the cam chain was pretty worn/stretched and it was hard to get TDC lined up. I wonder if the cam chain jumped a tooth. I guess I'll know soon enough.

camelman · « **Reply #14 on:** July 13, 2011, 08:27:52 PM »

Actually, I think that's it. I bump started the bike while rolling down a hill and it ran like crap afterwards. Would one or two teeth off create valve interference?

Grabcon · « **Reply #15 on:** July 14, 2011, 05:59:03 AM »

I don't know if these are interference engines or not. But what may happen is that one or both vales could be open during the compression stroke.

Ernest T · « **Reply #16 on:** July 14, 2011, 10:00:16 AM »

Most bikes are interference fit between piston and valves. Did the piston have depressions for valve clearance in the top? If so that's what they are there for. It doesn't take much ring or bore damage to lose the seal--those are measured in thousands of an inch after all.

dave500 · « **Reply #17 on:** July 14, 2011, 12:32:51 PM »

to have near zero compression wont be rings,itll be worse.

Grabcon · « **Reply #18 on:** July 15, 2011, 06:42:56 PM »

So what is the verdict? Did you find the problem?

camelman · « **Reply #19 on:** July 16, 2011, 09:38:30 AM »

Grabcon,

I was going to finish this yesterday, but scotch and a game of poker on Thursday night ended those ambitions... at least I won the game. However, I did pull the cylinder head and have found absolutely nothing wrong. The bores are fine, the valves appear fine and hold liquid in the chamber, and the timing chain did not skip. The head gasket show no sign of leakage, and the engine was not leaking oil anywhere.
The only strange thing is that the sawdust did not leave the cylinder. It is all in there, burnt, and has been joined by a lot of other carbon. The pistons had about an 1/8 inch of black powder on top, and the cylinder bores leave grit whenever the piston passes. I'll pull the cylinders this morning to see how the rings look, and will report back. I have a feeling the piston rings are completely gunked up with carbon. I'll get pics of everything I find.

This is getting frustrating!

Camelman

camelman · « **Reply #20 on:** July 16, 2011, 12:12:19 PM »

I pulled the cylinders to get a good look at the pistons. The pistons were super dirty, and had a slightly damp coating of carbon. The pistons in the cylinders show the carbon buildup, although that pic is after I wiped them down. The valves did not hold liquid as I thought though. I just didn't test them very well yesterday, but found them to not seal today.

The headValves pic show the same carbon on the heads of the valves without being wiped down.

PistonSide shows the pistons as they came out of the cylinders, and pistonSkirt shows typical wear marks on the pistons after they were cleaned.

DirtyCyl shows the buildup left on the cylinder walls after removing the pistons, although this is mostly due to me wiping the pistons while they were in the bores. Something I did not capture was the amount of light surface rust and gunk at the top of the cylinders.

WearMark shows where the pistons were wearing scuffs into the cylinders. These scuffs are very minor, and cannot catch a fingernail. I don't have a honing kit, but I did polish them lightly with 400 grit.

I also pulled all the valves and checked them. The exhaust valves were in good shape, and a quick lapping with rubbing alcohol had them clean and shiny where the contacted the seats. The intakes were a slightly different story. All four of them had small deposits on the seats that could have been sawdust. The deposits were at most a couple thousandths thick, but that is enough to create a large leak path for such small cylinders. I picked the particles off with my pocket knife and gave the intake valves the same honing with rubbing alcohol to clean them up. They cleaned up fine, and I reassembled the entire head.

So, nothing was burnt, nothing is broken, the cam chain did not skip... I think the problem was those intake valves being stuck slightly open. I am going to reassemble and start it up. The only issue I have is that I do not have a new cylinder head gasket to install. This one has 200 miles of driving on it, so I'm not sure if it is going to hold. However, I have a classic motorcycle ride i want to go on tomorrow, so I'm going to try it anyway. worst comes to worst, and I have to replace the head gasket... no big deal since the entire engine can come apart in the frame on a 350F!!!

camelman · « **Reply #21 on:** July 16, 2011, 12:12:50 PM »

last pic.

finkbuilt · « **Reply #22 on:** July 16, 2011, 12:27:09 PM »

Quote from: camelman on July 16, 2011, 12:12:19 PM

I pulled the cylinders to get a good look at the pistons. The pistons were super dirty, and had a slightly damp coating of carbon. The pistons in the cylinders show the carbon buildup, although that pic is after I wiped them down. The valves did not hold liquid as I thought though. I just didn't test them very well yesterday, but found them to not seal today.

Interesting. I am no expert by any means, but that buildup of material on top of the piston looks like way more than a little sawdust that snuck in through a spark plug hole, and was then wiped down before assembly.

Did someone put sugar in your gas tank?

mjstone · « **Reply #23 on:** July 16, 2011, 12:31:37 PM »

Wow, dude!

Looks like you got lucky. Must be a relief to find no real damage.

MJ

Hush · « **Reply #24 on:** July 16, 2011, 02:25:51 PM »

OK I guessed right, I want my chocolate fish!

dave500 · « **Reply #25 on:** July 16, 2011, 02:27:54 PM »

have the valves just got that oily/ sawdusty gunk on the seats and a simple clean and relap will fix it?

camelman · « **Reply #26 on:** July 16, 2011, 02:58:53 PM »

The valves were fine with only a slight carbon coating which was probably from the prior 4k miles I put on the head on the prior engine (I ported this head for the engine that failed a month ago, so I swapped it onto this engine when I installed it).

I started it up, and it runs well. I checked the oil and found that it was super low on oil, which is strange because I only rode it 200 miles. I filled it up, and will keep a close eye on it. I wonder if this whole issue started from low oil... the oil light never came on though. Super lucky I guess. By the way, Hush, I'm fresh out of chocolate fish. Otherwise, I'd mail you some ASAP. ;-)

Thanks everyone, and I'll make sure to post if this turns into a recurring problem. I did notice some white vapor out of the exhaust again when I started it. I'm hoping it is just water vapor. However, if it is fuel... Well, I'll cross that bridge when I get to it.

Camelman

camelman · « **Reply #27 on:** July 16, 2011, 03:02:50 PM »

Just to make it official, the actual cause was junk stuck between the valves and the seats. That option had the highest total of 8 votes, although it also said the valves were burnt... which they weren't. One interesting tidbit, the exhaust valves had no grit caught in them, only the intakes.

The second highest vote count was for the cavalry... I like the way you guys think.

The third highest vote... well, who really cares about the third highest vote.

;-)

Camelman

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Author Topic: Who wants to guess what broke in my second engine? (Read 2601 times)