Author Topic: Lost all compression (Read 5212 times)

Blue2swing · « **on:** April 01, 2018, 04:56:08 PM »

Happy Easter everyone,

I just drove my bike to my family's house for Easter. After arriving I tried to kick start the bike and heard a hissing sound like someone had pulled an air-hose off the bike. I then tried to electric start the bike and found there to be absolutely no oil pressure. I pulled one of the spark plugs and found it to be covered In soot. I just pulled and rebuilt the engine last year but rarely ride the bike. After a year of having this rebuilt bike I only have 36miles on it.

I tried to search for other post discussing "no compression" topics but keep getting an error message. I'm limited to searches on my phone till I get back home. If anyone can help with any ideas as to where to start my search I would definitely appreciate it.

Thank you

Keith · « **Reply #1 on:** April 01, 2018, 05:15:48 PM »

Make sure the cam is turning, broken cam chain?

Blue2swing · « **Reply #2 on:** April 01, 2018, 05:50:30 PM »

Thanks Keith. I'll take the tapped covers off to make sure I can see the cam turning.

I've been thinking about the hissing sound? Possible seal broken?? I just put new seals through out the entire engine. Any way of Checking if a seal is broken?

ekpent · « **Reply #3 on:** April 01, 2018, 08:08:31 PM »

Here is the old model, size, and year question. Is there zero resistance with the kick starter to show no compression ?

Blue2swing · « **Reply #4 on:** April 01, 2018, 08:11:49 PM »

I'm limited to what tools I have available here at my sisters house. I was able to remove one spark plug and found the entire thing covered in soot. I did not touch the carbs during my engine rebuild. I'm worried I have things running too rich which may be causing a build up of carbon deposits on the valves and plugs. Considering I'm using a socket that is the wrong size for the job I don't want to move any further on diagnosing the bike tonight. And I'm at an Easter BBQ and have yet to grab a plate of food or a drink!

I'm going to leave the bike here for the next couple of days and will pick it up on my day off to bring it back to my home garage workshop. Considering the soot built up on the spark plug im looking into possible non sealing valves and failing plugs. When I seated one of the possibily loose plugs and cranking the heck out of the bike the compression jumped up to 20psi. Soon still hopeful of this being a small problem.

Feel free to throw any suggestions as to what I should look for when I get the bike back. Thanks.

Blue2swing · « **Reply #5 on:** April 01, 2018, 08:14:25 PM »

Quote from: ekpent on April 01, 2018, 08:08:31 PM

Here is the old model, size, and year question. Is there zero resistance with the kick starter to show no compression ?

Sorry, the bike is a 1975 SOHC CB750 K5. When kick starting the bike everything turns like normal but the resistance is greatly diminished.

PeWe · « **Reply #6 on:** April 01, 2018, 10:22:23 PM »

The sound was most likely gas fumes that got ignited. My bike can fart like that when I turn on ignition, it depends on the fumes and position of ignition. No problems.

754 · « **Reply #7 on:** April 01, 2018, 11:17:53 PM »

Sounds like it could be head gasket, but it should still have compression on several cylinders.

dave500 · « **Reply #8 on:** April 02, 2018, 01:14:44 AM »

several cylinders?,#$%* is it a v8?

Yamahawk · « **Reply #9 on:** April 02, 2018, 04:30:05 AM »

Quote from: dave500 on April 02, 2018, 01:14:44 AM

several cylinders?,#$%* is it a v8?

Hehe... small block chevy.
Charlie

Kevin D · « **Reply #10 on:** April 02, 2018, 05:02:51 PM »

Quote

hissing

Spark plugs tight? Or loose?

Blue2swing · « **Reply #11 on:** April 02, 2018, 07:31:25 PM »

The hissing came from underneath the gas tank. Right near the spark plugs. At that time I had access to a socket that was too big for the plug, but was able to lock onto the plug enough to loosen it. I cleaned the spark plug and put it back in and, after some extensive cranking, was able to get the oil pressure to Jump up to 20psi. The oil pressure reads at 20psi now on every crank. I'm waiting on checking the other spark plugs until I can get the bike home so I can use the correct tools.

I have no experience rebuilding engines, and this is my first engine rebuild. I did everything by the book but I'm sure I may have unknowingly missed something somewhere. So far I'm $10K into this bike, lol. It's been a great experience and I'm learning as I go

Once I get the bike home, in about 2 days, I'll try to update everyone on my findings.

754 · « **Reply #12 on:** April 02, 2018, 07:51:22 PM »

Factory plug wrench works very well, although but looks crappy.
Dont expect to get good oil pressure cranking it over, without it running.

ekpent · « **Reply #13 on:** April 02, 2018, 08:12:47 PM »

First thing and easy to check is to see if you have spark. Crank over while a spark plug is grounded to the outside of the engine. Check your kill switch---------- and make sure you have enough gas in the tank

Blue2swing · « **Reply #14 on:** April 02, 2018, 08:57:45 PM »

Thanks ekpent, checking for spark, though a simple idea, did completely slip my mind. I'll add that to my list of things to review when I get the bike back. Considering how much soot was on the only spark plug I pulled I wouldn't be surprised if that is the problem. As I have gotten the oil pressure to return, some, but can't get the engine to fire. If that's the case I'll also have to look into cleaning the valves and seeing what I can do to lower the air to gas mixture. The carbs scare me, so I cleaned them on the outside to look nice, but left there inner parts alone.

Here's some pictures of the bike when I first got it. A picture of the bike during my custome wiring with Motogadget set up. And a picture of the bike pretty much complete. I did all the work myself, except for the powder-coating, seat upholstery, and I popped a couple of tubes trying to mount the front tire, so paid to have that done as well

. Everything else was done by me, and I had no idea how to do any of it before the project started, including the welding, so it was a lot of fun and a lot of learning.

Paintedseat · « **Reply #15 on:** April 02, 2018, 10:07:12 PM »

Is that a CycleX exhaust

Blue2swing · « **Reply #16 on:** April 02, 2018, 10:50:46 PM »

Yes, the SOHC sidewinder. I personally think the DOHC model looks better (it's a little longer) but it's only compatible with the SOHC bikes after modifications to allow clearance for the brake pedal. And the DOHC model is a pain to fit onto the SOHC head, but it's doable.

PeWe · « **Reply #17 on:** April 03, 2018, 12:58:35 AM »

Last pic: Bike looked really good as stock

Blue2swing · « **Reply #18 on:** April 10, 2018, 06:27:30 PM »

Thanks PeWe, I had a hard time beginning the project because the original bike was in such good condition. I even debated buying a second bike for the project! What happened is I made up my mind that I was going to build this bike. I did 2 years of research (buying and reading Manuals, watching YouTube videos, and hours and hours of reading on this forum). The first major milestone of course was actually acquiring the bike, so after the 2 years of casual research I purchased this gem on eBay for $3k. The pictures looked decent but I was really expecting to be disappointed with the actual bike. I assumed the pictures were taken at just the right angles to hide any blemishes. To my surprise the bike was not a disappointment at all and exactly like in the pictures. I got many complements drive long this bike around town stock which is what made it so hard to continue with the project. I looked for a second 75 CB750K everywhere but as you may know in the west coast these bikes are hard to come by. I did find a couple beat up K5's however the sellers always wanted around $3k for their non-running bikes and I couldn't pay that again when I already had gotten mine for the same price. So, with no luck finding a second bike I decided to continue the project with the bike I already had. Not. Knowing what I was doing I took my time and paced myself. The rebuild itself and custom fab work took me another 2 years (total project time of 4 years for learning about the bike, learning how to ride a bike and get my license, learning how to weld, learning how to rebuild a combustion engine, etc). I really was like a baby at the beginning of the build, had not a single idea or ounce of experience with what I was doing. Considering that, I'm extremely happy with the end result! I'm still learning however and have much to learn

Blue2swing · « **Reply #19 on:** April 10, 2018, 06:45:25 PM »

Finally got the bike back home and had a chance to pull the plugs. The problem ended up being no spark due to dirty spark plugs. I cleaned off the plugs and put them back in and everything fires right up. The bike sounds amazing again and oil pressure is where it should be! After 5 minutes of running the bike I stopped the engine and pulled the plugs For inspection. The plugs where full of soot again. I'm guessing this is due to running too rich of a fuel mixture? Anyone have any ideas on how to correct that?

I'm going to look in the manual and do some reading online for a solution shortly. I just wanted to fill you all in on what the problem was and thank you again for the advice.

ekpent · « **Reply #20 on:** April 10, 2018, 07:49:13 PM »

Some weird looking plugs, what brand and number are they ? Could be too rich on the carb jets,too much oil on your pods, wrong plug heat range or bad spark, all kinds of fun stuff.

dave500 · « **Reply #21 on:** April 10, 2018, 08:51:33 PM »

are you operating the choke correctly?

Blue2swing · « **Reply #22 on:** April 10, 2018, 10:19:47 PM »

Quote from: ekpent on April 10, 2018, 07:49:13 PM

Some weird looking plugs, what brand and number are they ? Could be too rich on the carb jets,too much oil on your pods, wrong plug heat range or bad spark, all kinds of fun stuff.

I found a section in the shop manual stating that running cold plugs will contribute to the build up in carbon.

I'm running NGK D8EA plugs. They are what came with the "tune-up" kit from one of the online SOHC parts suppliers. The Shop manual says to use NGK D7ES (I believe the D8EA is the replacement for the D7ES, the D8EA is also known to be a colder plug than the D7ES). The D7ES is suppose to run hotter which allow the plugs to burn off the carbon build up, or so that's what I'm reading in this forum (http://forums.sohc4.net/index.php?topic=77832.0).

In the same post Homdaman is recommending the Nippon Denso X24ES-U instead of the NGK D8EA. I may have to buy both the X24ES-U and see if I can find a set of D7ES to try each out and see what effects they have on the carbon build up.

Quote from: dave500 on April 10, 2018, 08:51:33 PM

are you operating the choke correctly?

I don't know. Possibly not

. I'm running the choke only like the owners manual suggests. I lift the lever all the way to the top position during start ups, then immediately lower it all the way down to the bottom position afterwards.

I'm intimidated by the carbs and try to touch them as little as possible.

dave500 · « **Reply #23 on:** April 10, 2018, 10:24:39 PM »

no worries a couple of guys have gotten that action wrong in the past,are the plug wire caps the original old ones?check their resistance they may need replacing,they unscrew from the wires end.

Don R · « **Reply #24 on:** April 10, 2018, 10:35:24 PM »

I couldn't find the denso's locally, Rock Auto got me a set in a few days and about the same price even with shipping.

News:

Author Topic: Lost all compression (Read 5212 times)