So, some of you read my post about my trip out to Denver and back. I really enjoyed the trip, and was quite sore after the trip and took a little break from the hawk and rode my dirtbike. Well, about 2 weeks after I decided that I wanted to go somewhere on the hawk. Went out to start it and it cranked without starting. I figured that it might have something to do with running into the mountains. Pulled the plugs to see if they were fouled (this after smelling raw fuel out the pipes), they weren't bad. SO...

Just did a compression test- 30 psi front, 40 psi rear. I am going to pull the valve cover and see where that gets me (valves), but I checked it last year, so it shouldn't be that. I guess I have to dig further...

My point for the title, I am lucky the bike made it back.

 

shoot, thats pretty weird without an overheat or cct failer. So what's the plan if it needs to be rebuilt?

 

Checked the valves on the rear cylinder, they are loose. Looks like the heads are coming off. carbureted bikes suck in the mountains, and I am guessing that this is the aftermath.

 

I noticed it's your Birthday. Well happy Birthday!

some thoughts about your bike:

Your bike ran normal throughout the trip.
You parked it for a while, and when you went to start it turned but wouldn't start.
It seems likely that the things you're checking would have occurred gradually and would have at least displayed symptoms of degrading while riding.
You smelled fuel. maybe the diaphragm in the petcock is leaking?

 

Measured the compression already. no compression.

 

I don't see how running in the mountains could have done anything to the bike.

Sure it would have been down on power while up at altitude, but that's it.

Did you check your oil to make sure there is no gas in it? If your petcock leaked, and your floats stuck, gas could have flown past your carbs into your cylinders and that could have damaged things. (possibly quite harshly when you cranked it)

see: https://www.superhawkforum.com/forum...ad.php?t=18307

 

Nope, no gas in the bottom end. The bike is jetted for under 500ft, and on the rich side. I ran up to 12,000 feet before I feared that it would not run if I shut it off. Kept it running and got back into Denver. I rode 900 miles on the last day and never had any trouble starting. Tried almost two weeks ago to start it, and it cranked but wouldn't start. The rings could have got carbon'd up and stuck, but I will know more after I open it.

 

so, low compression and free valves... pulling cylinders

 

Usually a sudden loss of compression after running well last time it was ridden is due to timing chain/belt failure during start-up (I've seen it many times on cars), but that doesn't explain the loose valves. I assume you cranked it with the valve covers removed, and checked valve timing.

Altitude should not be a factor. You'll just run richer than normal. I've had my SuperHawk up to over 6,000 feet a number of times. It actually runs better up there with stock jetting.

In any case it sounds like you'll find the cause soon. Good luck and keep us posted.

 

Soft carbon deposits can keep the valves from closing and will cause low compression. Running rich will increase carbon deposits.

 

If you're running that rich, you'll foul the plugs before you get any amount of carbon on the valve face or seats. They pretty much self clean when they close.

From my experience, zero to 40 psi compression is burned/bent valves or timing chain/belt problem. Come to think of it, bent valves will cause excessive lash, since they won't close completely.

 

It is sounding like CCT failure on startup..

 

Nope, nope, and nope.

replaced ccts last year, and I know what bad ones sound like.

No smashed valves, no over rev on trip

valves are at the correct amount of lash, did that last year

if I had shut it off to full cold outside of Vail, it would have never started with those plugs

If it were valves.timing chain related, how would I have had simultaneously dropped both cct's, or better yet, what is the chances of having both cylinders out because of smashed valves with no over rev and no broken ccts.


Possibilities are:
burnt/carboned valves (doesn't increase lash noticeably)
carbon'd rings

 

Well I hope you figure it out.. Keep us informed!

 

I will be pulling the heads off this week, and I will take pics of whatever I find.

 

Suspense...I don't see anything that would cause the compression to drop in both cylinders at once, definitely not valvetrain related since they are separate on both cyls.
I vote for carbon that locked the rings in their groove, pistons chill and pull the rings away from the walls, other than this and unlikely, but worth to consider.
Defective compression tester
Fractured or burnt piston due to detonnation (unlikely since you are jetted rich)
Blown head gaskets due to overheating (you should know if this happened)

 

To me, the symptoms doesn't add upp... One piece of the pussle is missing... I hate that... I can't stop mulling it over... Get yer rear in gear and pull it apart and put my mind at ease...

 

Never seen it happen on a bike but have seen it on a few cars during the last 25 years of working at a Honda dealership.

 

sorry to keep you all waiting, but my camera is dead...

And my allen wrenches are missing.

 

Did you try pouring some heavy oil down the cylinder then check the compression that would tell you if the rings are the culprit.

 

No I didn't, but it doesn't really matter if I dont have compression. The heads are coming off anyway...

 

A lot of people drove the hell out of Hondas never knowing the valves require adjustment every 15,000 miles. And if you're not careful with the auxillary intake valves on the CVCC engines you'll adjust them tight, as you know, allowing carbon build-up.

I taught Vocational Automotives for 34 years in a 10 bay shop in Garden Grove, and my students drove mostly Hondas and Toyotas for the last 15 or more years. We did tons of valve adjustments, and we worked as a commercial shop 2 days a week, taking in customer cars.

Also I can't see rings even entering the picture, since the compression is so low. A ring problem usually doesn't lower the compression below 80 or 90 psi. A hole in the piston or burned piston = mucho oil smoke out the exhaust.

I'm guessing bent valves.

 

How would the valves get bent? It did not have a cct failure, and did not over rev. Did all 8 valve springs give up and let the valves float at 6k rpm? This is carbon related, and I am sure that I did not hole both pistons.

And, wouldn't I notice a unreasonably large gap at the buckets? Its not so, so I don't think that is the issue. I will post pics when I pull the cylinders

 

I hear you. This is a weird one, but I just can't see that much carbon on the valve seats to cause zero compression, or even near zero. The slamming of the valves closing should wipe off any carbon, and again the plugs would foul first, causing misfire.

I'm hoping you find a problem that requires an inexpensive fix, seriously.

 

Just my .02 but before I would condemn an engine I would verify the gauge. Just a thought and might not be the gauge just check it on an operating engine before you break cases.

 

I just sat here and read this entire thread, and I agree with nuhawk, check the guage first.

Unless there is something your not telling us then I don't think you have any internal damage. You may have been running way too rich, but probably not enough to build up carbon on the rings like that. I'm thinking that would take substantially longer than the period of time your are talking about. Like months of running rich.

 

Well, I have to pull the oil pan to sneak the rods and pistons out, but here is the preliminary results:





Something, besides the enormous amounts of carbon that is covering the piston and the little bit of exposed cylinder, is that the valve seats are not trimmed flush with the combustion chamber. Did anyone else have that on there head when they took it off? I am condemning the rings, as the VALVES ARE NOT SMASHED. I am not saying that they are sealing 100%, but I am going to clean that up prior to reassembly.


Update:valves also have carbon deposits on them. Its like cancer, it flaked off cylinder, head, and piston and made it onto the faces and seats of the ex. I am sure the rings have seen similar "damage". I will be able to clean the valves and bring them back to life.

 

Ex valves had a easily removed "flake" carbon. The compression numbers and the amount of carbon in the cylinder has me wanting to pull the slugs and clean the cylinders.

Is there a chance, for those who have tore down their engines, that the piston and con rod can be removed just be pulling the oil pan?? I just dont feel comfortable with going through the motions of cleaning the valves, and ignoring the bottom end, spending the money to put it back together, to end up with marginal compression and more time invested.

 

Pretty sure you can Bill. Some people have put in high comp pistons without a full disassembly.

Bit of a weird problem. I would have thought with compression that low the bike would have performed terribly on your last ride. That much carbon build up needs smore thought given to it, as you need to find out why it has happened.

 

12000 feet extended ride, followed with 6-7000 feet for two days on a bike that was jetted on the rich side at 500. That is my guess.