Author Topic: Fighting with siezed engine (Read 2310 times)

danyo · « **on:** July 08, 2015, 09:01:44 PM »

Hi guys. 76 Cb 750, last registration 1981 so probably that year bike was abandoned. Odometer shows 3500 miles but no way to confirm that. Anyway, can't turn the engine. Atf/acetone in jugs (not much but can see pistons covered). Next day 5 gear and rocking back and forth. Nothing. I know I should wait more days, just trying, but no signs of my mixture in jugs. Refilled with PB Blaster again to cover up pistons. After 24 hours no signs of penetrant in jugs. Good sign?? (not rusted rings) or bad sign?? When you look through spark plug hole in cylinder 1,4 jugs looks nice without any rust. I'm thinking maybe pistons are free but valves siezed. What you recommend in that situation. Where to put penetrant to try to unstuck valves. Engine is still in frame. After reading stories about freeing motors without rebuilding them I would like to try that route - especially if mileage is original and I can save some time and money on rebuild. I don't think there are any other parts that can easily get seized? Waiting for your opinions.

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70CB750 · « **Reply #1 on:** July 09, 2015, 04:22:16 AM »

I think it's time to pull the engine and take the head off.

calj737 · « **Reply #2 on:** July 09, 2015, 04:33:05 AM »

Before you remove the engine, pull the oil drain plug. How much fluid comes out? Typically, the piston(s) at BDC are the ones that rust up. So if 1/4 are TDC, 2/3 are likely your issue.

Only use the bolt under the stator cover to rotate a stuck engine. Something else to try: go get some Kroil brand penetrating oil. It's unusually good for things like this. But you do need to try and track how much is going in, and how much is passing thru to determine whether or not you're actually making progress. ATF/Acetone works, but the Acetone evaporates too quickly to use a determinant for seepage.

Once you get the engine to rotate, fully change the oil and filter.

Phinn · « **Reply #3 on:** July 09, 2015, 04:38:37 AM »

Pulling and rebuilding is not that difficult. The engine is relatively simple, once you understand what everything does. And even if it's just the valves, you still have to pull the engine to service them, or cut the frame and install one of those removable sections.

danyo · « **Reply #4 on:** July 09, 2015, 06:19:25 AM »

Thanks guys for replying. I'm not scared to pull the engine and rebuild (I did k7 last winter) but that will be last option. I never tried to unstuck siezed engine so that's new experience which I want to tackle

. I will try for few days refill jugs with penetrants, get some kroil like Cal suggest and try more. When I will use bolt under stator to rotate, bolt will start to unscrew if to much force counterclockwise is applied. Should I try to rotate motor backwards??

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calj737 · « **Reply #5 on:** July 09, 2015, 06:21:10 AM »

If it unscrews, the motor is still stuck. That's really the barometer for it being ready to rotate. You can budge it backwards just to break it loose, but I'd avoid full rotations clockwise given the uncertainty of the internal condition.

danyo · « **Reply #6 on:** July 09, 2015, 06:40:52 AM »

Ok understand.

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DaveBarbier · « **Reply #7 on:** July 09, 2015, 04:41:17 PM »

I've never done this, but I've heard some people on here saying they used a grease gun. If a piston is at top dead center of its compression stroke (actually between the compression and power strokes) you could somehow fit a grease zerk into the spark plug hole with an adapter of some kind then pump away and fill up the combustion chamber. You can generate a lot of pressure with a grease gun.

calj737 · « **Reply #8 on:** July 09, 2015, 05:15:54 PM »

Quote from: DaveBarbier on July 09, 2015, 04:41:17 PM

I've never done this, but I've heard some people on here saying they used a grease gun. If a piston is at top dead center of its compression stroke (actually between the compression and power strokes) you could somehow fit a grease zerk into the spark plug hole with an adapter of some kind then pump away and fill up the combustion chamber. You can generate a lot of pressure with a grease gun.

This does work. The only reason I didn't recommend it is his hope is to avoid splitting the engine. If you do use grease, you really ought to pull the head to get all the grease out entirely. Harder to do assembled.

DaveBarbier · « **Reply #9 on:** July 09, 2015, 06:27:58 PM »

Quote from: calj737 on July 09, 2015, 05:15:54 PM

Quote from: DaveBarbier on July 09, 2015, 04:41:17 PM
I've never done this, but I've heard some people on here saying they used a grease gun. If a piston is at top dead center of its compression stroke (actually between the compression and power strokes) you could somehow fit a grease zerk into the spark plug hole with an adapter of some kind then pump away and fill up the combustion chamber. You can generate a lot of pressure with a grease gun.
This does work. The only reason I didn't recommend it is his hope is to avoid splitting the engine. If you do use grease, you really ought to pull the head to get all the grease out entirely. Harder to do assembled.

Ah, true, didn't think of that.

danyo · « **Reply #10 on:** July 09, 2015, 07:37:52 PM »

Believe it or not engine is free!!! More penetrant, heat gun and a lot of rocking. It give up slowly but I was able to see crank movements. After one full rotation I was able to rotate it with rotor bolt. It has compression so hoping for runner soon. Any recommendations what to check before firing it. I'll change oil, plugs, clean carbs. Should I drop the oil pan and check for debris or not necessary?

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Stev-o · « **Reply #11 on:** July 09, 2015, 08:37:13 PM »

Yo Dan...have not heard of heat gun method. You heated the cylinders?

danyo · « **Reply #12 on:** July 09, 2015, 08:52:30 PM »

Yep. I always use heat to unstuck slides in carburetors. I thought it can't hurt, I used heat gun but others use Mapp torch to heat up cylinders. I think it really depends how badly it's siezed. I had good feeling that mine isn't that bad. Now the fun begins and worst part is - not enough time for hobby due to work and kids vacation

. I believe my next fight with sized engine will be on K1 which I bought from Drew from Kansas. I was angry at you Stev-o that you stole gauges and triple tree from that bike but there is more missing parts so I'll be looking for them when time comes.

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70CB750 · « **Reply #13 on:** July 10, 2015, 04:01:43 AM »

Definitely drop the pan and see whats in there and clean the oil pump screen too.

Stev-o · « **Reply #14 on:** July 10, 2015, 04:01:54 AM »

Quote from: danyo on July 09, 2015, 08:52:30 PM

I was angry at you Stev-o that you stole gauges and triple tree from that bike but there is more missing parts

I still haven't closed a deal on those! The seller hasn't responded to my last PM a couple days back.

danyo · « **Reply #15 on:** July 10, 2015, 07:58:14 AM »

I know he's out of town until Sunday. I didn't pick up bike yet but I will asap. Let me know if you'll pass on those parts, I gladly have that bike complete as much as possible. Thx

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flybox1 · « **Reply #16 on:** July 10, 2015, 08:25:07 AM »

i'd try and knock out as many of the 3000mi maintenance items as i could before firing it. Give it a good shot at starting and running the first time you hit the starter.
valve lash, cam chain adjust, check points gap and clean,
oil pan, clean oil pump screen, and kick it over while the pan is off to expel any goo...new oil (spread one qt up top between the intake valve tappet holes), new plugs, plug caps. strong battery....

danyo · « **Reply #17 on:** July 10, 2015, 09:00:50 AM »

Thanks flybox1. Yes I will do full tune up but in the first order - good bath - bike deserves it after 40 years, hahaha

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Phinn · « **Reply #18 on:** July 10, 2015, 10:12:07 AM »

Clean out the gas tank and fuel lines. After that much time, old gas precipitates solids, and any moisture in the old fuel causes rust.

rotortiller · « **Reply #19 on:** July 10, 2015, 10:45:21 AM »

There is a concern I'd have with pressurizing one cylinder with grease. While the grease pressure load is distributed across the piston crown and it may break loose safely you have to consider the other seized pistons. The resultant load to free them will be localized on the rod bearings and not piston crown which could cause strain. Might be better to pull the cam and grease pressurize the 2 inner pistons at the same time for a tiny bit then swap out to the two outer 2. Not sure what the maximum safe PSI would be but grease guns can supply a lot of pressure.

danyo · « **Reply #20 on:** July 10, 2015, 11:31:21 AM »

I did not even consider grease gun method in my situation. That would be the option if I have engine out of frame and be ready for rebuild. I'm aware that even if I will be able to start that motor, it can be weak, low compression or other problems due to seizing, time will tell. Top end looks tight. No signs of old oil leaks around head gasket or anything so I wanted to try not open it. Maybe it's low mileage and will work like new - will see

.
Regarding tank. It is very clean inside. It was repainted at some point and has some dents from something dropping on it but that's it. Probably PO get rid of the fuel when he parked it. Not even one spot of rust inside. Carbs are clean also except 1st body from residual fuel getting to it from parking on a side stand.

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Stev-o · « **Reply #21 on:** July 11, 2015, 01:52:08 AM »

Quote from: danyo on July 10, 2015, 07:58:14 AM

Let me know if you'll pass on those parts...

I need them for my K1 I will be restoring later this year.

danyo · « **Reply #22 on:** July 11, 2015, 06:48:02 AM »

^^^ just tried ; )

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Author Topic: Fighting with siezed engine (Read 2310 times)