Author Topic: Stuck motor? (Read 2734 times)

wicat · « **on:** March 24, 2011, 02:24:50 PM »

Hey guys i have a 73 honda cb750K3 and ive teared the motor down to the point were i need to remove the pistons and found that the pistons are stuck in the block and i cant seem to free them up. Ive soaked the pistons in mystery oil and tryed spining the flywheel with a pry bar so far nothing has worked. My question is do i bother having the pistons machined out or look for a place like cycle X with an exchange program.

GammaFlat · « **Reply #1 on:** March 24, 2011, 02:47:54 PM »

You'll be able to free it up. Assuming it is a stuck piston (which it likely is), Put a 50/50 mix of acetone and trans fluid in the cylinders. I did a little tapping with a 2x2 block of wood on the tops of the pistons. I also hooked a jumper cable to the starter cable (black/negative to ground and red/positive to the starter cable). It seems the starter did a better job than trying push on the kick lever with my hand.

wicat · « **Reply #2 on:** March 24, 2011, 03:30:45 PM »

thanks ill have to give that a try. I never thought of doing the starter. lol

GammaFlat · « **Reply #3 on:** March 24, 2011, 03:31:44 PM »

Quote from: wicat on March 24, 2011, 03:30:45 PM

thanks ill have to give that a try. I never thought of doing the starter. lol

Wear goggles

Stev-o · « **Reply #4 on:** March 24, 2011, 05:48:14 PM »

Let the aft/acetone soak for a few days. Most likely, the rings have rusted to the cyl. I was able to free mine up.

ekpent · « **Reply #5 on:** March 24, 2011, 06:19:20 PM »

OK now not trying to start a big debate or fight but I have read about the ATF/Acetone miracle cure before,tried it on a two stroke Yammie twin with no success.Why is it better for the folks than a product like Kroil I think its called,or other products or is it a myth that has perpetuated itself here

Does it soak.penetrate and release better than most products.Lets hear the real science behind it.

MCRider · « **Reply #6 on:** March 24, 2011, 06:46:02 PM »

Quote from: ekpent on March 24, 2011, 06:19:20 PM

OK now not trying to start a big debate or fight but I have read about the ATF/Acetone miracle cure before,tried it on a two stroke Yammie twin with no success.Why is it better for the folks than a product like Kroil I think its called,or other products or is it a myth that has perpetuated itself here Does it soak.penetrate and release better than most products.Lets hear the real science behind it.

Two-Tired posted the results from an engineering magazine of a comparison of penetrants. I found the link but it now has a 404 error.

http://www.sohc4.us/forums/index.php?topic=20131.msg209311#msg209311

It compared in a semi scientific way the efficacy of the top 5 or so commercial penetrants: WD40 by far the worst, PB Blaster, Kroll, Liquid Wrench, a couple of others, and a 50/50 mix of ATF and Acetone. The ATF/Acetone cocktail had them all beat by at least a factor of 2 and more in most cases.

I'll keep searching for the link.

BobbyR · « **Reply #7 on:** March 24, 2011, 06:47:32 PM »

Quote from: ekpent on March 24, 2011, 06:19:20 PM

OK now not trying to start a big debate or fight but I have read about the ATF/Acetone miracle cure before,tried it on a two stroke Yammie twin with no success.Why is it better for the folks than a product like Kroil I think its called,or other products or is it a myth that has perpetuated itself here Does it soak.penetrate and release better than most products.Lets hear the real science behind it.

Somewhere buried in the past is a University report on various products and the homemade ATF/Acetone mixture. The homebrew beat everything by a lot. The Acetone thins the oil out to a point it wicks better, evaporates and leaves behind the oil. Acetone is so volatile it evaporates almost immediately, that makes it a non viable commercial product.

If you pour it in the cylinders the Acetone will be gone quickly, so you may need repeated applications.

CB750F2 · « **Reply #8 on:** March 24, 2011, 07:01:08 PM »

This is the link to the tests.
http://forums.sohc4.net/index.php?topic=20131.0
Pat

MCRider · « **Reply #9 on:** March 24, 2011, 07:07:09 PM »

Thanks Pat, that's what i was looking for.

GammaFlat · « **Reply #10 on:** March 24, 2011, 10:49:35 PM »

I have "unstuck" 750 motors with it. We tried to unstick my brother's small block Chevy with it and it wouldn't work until we found there was a bolt in the flywheel hung up on the engine stand bracket. It was never "really stuck".

scottly · « **Reply #11 on:** March 24, 2011, 11:02:45 PM »

Quote from: ekpent on March 24, 2011, 06:19:20 PM

OK now not trying to start a big debate or fight but I have read about the ATF/Acetone miracle cure before,tried it on a two stroke Yammie twin with no success.

Two strokes usually seize from under-lubricating/over-heating the pistons. Ask me how I know. I'll also tell you about which OIL is the best to use in a two stroke.

ekpent · « **Reply #12 on:** March 25, 2011, 07:53:01 AM »

Thanks Guys and Gals. I am now a believer.

dave500 · « **Reply #13 on:** March 26, 2011, 05:41:31 AM »

there are are lot of unsticking engine threads,,truly though once an engine is unstuck,it should be taken apart,lots are goers,the rings wont really be free and the rust that has been dislodged is only going to cause abrasion elswhere throughout the engine,,im sure theres tales of stuck engines with second lives,its not really good practise though to run them,wheres all the crunchy stuff gone?,,,just ignore it,,the engine runs,the filter will pick it up,,then on the other hand guys will get hung up on using silicone as gaskets because little bits will flake off and cause havoc?jeepers,strip the motor and do it right,your losing horspower if thats what your interested in,i only unstick engines to get them apart,sure if its an easy unstick,but soaking for days then running it as a good goer?bad short cuts boys.

ekpent · « **Reply #14 on:** March 26, 2011, 06:07:13 AM »

We have seen some pretty sick looking engines that have been opened up on here with rust issues etc. that's for sure.I would agree that if it has sat outside for any length of time especially and is seized it probably a mess.

dave500 · « **Reply #15 on:** March 26, 2011, 06:23:20 AM »

i think that you shouldnt get your hopes up that a seized engine will come back to life and have as much enthusism as you do,sure get it turning,,but pull it down,these cheap and lazy runners end up as someone elses rebuilds,,the old ,,lost interest,or "unfinished"project aint it all may seem,,someone else has had a go at it,,and it needs time and money,if you finish and keep what your unsiezing,youll only be on half power,do it right,or dont do it.

Blasbo · « **Reply #16 on:** March 26, 2011, 06:53:29 AM »

Dave, I was thinking the same thing you said. Even if I do get my engine unstuck, what about all the crap and gunk in there? Also what should I do once I get it unstuck? Clean it out, put it back together and check compression? Or should I replace the rings while I've got it open?
I tried ATF/acetone with no luck. It got me to wondering if the test was one time only or if it was repeated multiple times and the reslts averaged? Some engines aren't as stuck as others, right?

dave500 · « **Reply #17 on:** March 26, 2011, 06:59:56 AM »

some engines aint as stuck as others to be sure,some just need a little(the operative word here)persuation,you have to bite the bullet,these are a high rpm engine,and fairly precise for what they are,you expect a lot out of them,,you have to give them some decent input,if you aint happy with the unstick feel,,do take it apart.

Hondawggie · « **Reply #18 on:** March 26, 2011, 08:28:47 AM »

Quote from: Blasbo on March 26, 2011, 06:53:29 AM

Dave, I was thinking the same thing you said. Even if I do get my engine unstuck, what about all the crap and gunk in there? Also what should I do once I get it unstuck? Clean it out, put it back together and check compression? Or should I replace the rings while I've got it open?
I tried ATF/acetone with no luck. It got me to wondering if the test was one time only or if it was repeated multiple times and the reslts averaged? Some engines aren't as stuck as others, right?

I used the atf+acetone and freed-up a stuck '73 750. I let it sit for 2 weeks, then I went to check the progress, I lowered it off the centerstand, I forgot that I had left the bike in 5th gear (which you want to use as opposed to 1st or 2nd gear etc. due to the favorable leverage you get having it in 5th gear when you rock the bike back and forth to free it up).

I dropped the bike off the center stand and when the back wheel hit the ground, it freed up the pistons then and there since it was still in 5th gear.

But it did take 2 weeks.

About a year later I tried it on a 4 cylinder Kz Kawasaki. That time the atf+acetone failed to make an impression. It became a parts bike as it was complete.

So it doesn't always work.

Stev-o · « **Reply #19 on:** March 26, 2011, 10:14:50 AM »

Hwiggie - did you get it running yet? If yes, how is it?
You inspired me to "unstuck" mine last year, but I have yet to be able to attempt a startup (damn kitchen remodel!)

Hondawggie · « **Reply #20 on:** March 26, 2011, 11:14:03 AM »

Quote from: Stev-o on March 26, 2011, 10:14:50 AM

Hwiggie - did you get it running yet? If yes, how is it?
You inspired me to "unstuck" mine last year, but I have yet to be able to attempt a startup (damn kitchen remodel!)

Congratulations on getting it freed up, its great to find you have something to work with.

I have been procrastinating it because of the hassle of popping the motor out of the frame and the rebuild then reinstalling. It is in the garage, meanwhile since then I've been busy with 2 kz650s, one successfully the other a donor parts bike, a cb900 and a kz1000 revival. Took the easy road because it was the shortest path to having wheels. But I will get to it. Thing is that after it's freed up you pretty much have to assume it will need rings and a hone, minimum, and if condensation was enough to stick the pistons the valve stems are oxidized probably and so you need a valve job, so a full engine rebuild for this guy is coming.

GammaFlat · « **Reply #21 on:** March 26, 2011, 11:26:06 AM »

A lot of guys would say that it needs a rebuild after being "un-stuck" but a lot of other guys have gotten lots of miles on bikes after they "un-stuck" them. I guess it depends on how bad the cylinder walls are.

Johnie · « **Reply #22 on:** March 26, 2011, 02:57:13 PM »

Well check this pic out...this is a stuck CB750K4 that I bought as a parts bike with 4,700 miles on it. The guy bought the bike new, rode is a year or 2, bought a Harley and let the K4 sit for I don't know how many years. I have been soaking this on and off for a year now as I have not needed it. After seeing this thread I have now soaked the area with Liquid Wrench as the PB Blaster did not help. I have not tried the acetone/tranny fluid yet, but that could be next. Once I let it sit for a while I use a dead blow hammer with a wood block to protect the pistons. I was wondering is maybe my automotive air hammer might work? I could use a block of wood or could use it in direct contact with the piston tops. Your thoughts on banging it out??? Click the pic to enlarge it...

Old Scrambler · « **Reply #23 on:** March 26, 2011, 05:54:54 PM »

Johnie.........take 4-2x2 lengths of good wood and drill holes to match the case studs and bolt them together on the top and bottom of the barrels. Set the barrels on a large sturdy bucket or wheelbarrow and fill the tops of the cyclinders with the ATF-Acetone mix. Let stand for a week or so. You should be able to push the pistons out.........block of wood and rubber hammer, or a clutch or steering-wheel puller on reverse. The wood will protect the cylinders and give you a place to clamp-on.

This also works for cylinders still on the cases........just bolt the wood strips to the top for leverage and protection. I used a hardwood plank and cut holes in it for the cylinders. Success on one each of a K3, K8, and F2 motor.

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Author Topic: Stuck motor? (Read 2734 times)