Author Topic: Engine rebuild problems?  (Read 1702 times)

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Offline RayT

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Engine rebuild problems?
« on: August 13, 2014, 07:53:52 am »
Hi all.

I've started rebuilding my CB750 engine.

After refitting the engine casings and torqued all the bolts it is very hard to turn over the crank .

It will not spin by hand, it only turns over with the aid of a bar. This is with no barrel or head fitted.

I am assuming this is not right, but I have no guide as to how hard/easy it should turn over as the rings were locked in the barrel on one cylinder before stripping the engine.

Could anyone point me in the directions of what to check ?

Cheers.

Ray

Offline MCRider

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Re: Engine rebuild problems?
« Reply #1 on: August 13, 2014, 08:01:03 am »
The crank alone should spin easily by hand. You've got a tight bearing, lack of prelube, or something going on. IT is fouled by the chains and trans so you have to feel for it.
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Ron
1988 NT650 HawkGT;  1978 CB400 Hawk;  1975 CB750F -Free Bird; 1968 CB77 Super Hawk -Ticker;  Phaedrus 1972 CB750K2- Build Thread
"Sometimes the light's all shining on me, other times I can barely see, lately it appears to me, what a long, strange trip its been."

Offline 70CB750

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Re: Engine rebuild problems?
« Reply #2 on: August 13, 2014, 08:01:39 am »
When my half rebuild engine would not turn over, usually the cam chain was binding on the lower sprocket.

If that's not the problem, I would think an oil ring is the culprit.

Edit:  my bad, barrel means cylinders, right?

Offline MCRider

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Re: Engine rebuild problems?
« Reply #3 on: August 13, 2014, 08:12:40 am »
When my half rebuild engine would not turn over, usually the cam chain was binding on the lower sprocket.

If that's not the problem, I would think an oil ring is the culprit.

Edit:  my bad, barrel means cylinders, right?
barrel = cylinder

Gads I hope he's not turning it with a bar against the cam chain, though that's possible. Damage done.
Ride Safe:
Ron
1988 NT650 HawkGT;  1978 CB400 Hawk;  1975 CB750F -Free Bird; 1968 CB77 Super Hawk -Ticker;  Phaedrus 1972 CB750K2- Build Thread
"Sometimes the light's all shining on me, other times I can barely see, lately it appears to me, what a long, strange trip its been."

Offline RayT

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Re: Engine rebuild problems?
« Reply #4 on: August 13, 2014, 08:16:45 am »
Hi guys thanks for the response.

I have no barrels or head on the engine and it is still tight to turn over.

I  prelubed the bearing shells and torqued bolts.

Is there a specific engine sealant to use on the main casing as it seems no gasket is available?

I have used Wurth RTV sealant which seems light in viscosity .

@ MCRider yes Barrel = Cylinder . No turning at the crank itself not cam chain.

Offline MCRider

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Re: Engine rebuild problems?
« Reply #5 on: August 13, 2014, 08:24:35 am »
Hi guys thanks for the response.

I have no barrels or head on the engine and it is still tight to turn over.

I  prelubed the bearing shells and torqued bolts.

Is there a specific engine sealant to use on the main casing as it seems no gasket is available?

I have used Wurth RTV sealant which seems light in viscosity .

@ MCRider yes Barrel = Cylinder . No turning at the crank itself not cam chain.
You should use a non-hardening sealer on the case halves, most popular is GasgaCinch. It should not harden and should not contain silicone that hardens. It will squeeze to the inside, harden and flake off. Travel like a blood clot to the oil orifice in the head and smoke your cam sure as can be.

To the problem: Slowly loosen each main bearing bolt one at a time till the crank turns easily. That will get you started anyway. But I'll bet it needs to come apart and be looked at, for debris on a bearing shell, or a shell that's not seated etc.
Ride Safe:
Ron
1988 NT650 HawkGT;  1978 CB400 Hawk;  1975 CB750F -Free Bird; 1968 CB77 Super Hawk -Ticker;  Phaedrus 1972 CB750K2- Build Thread
"Sometimes the light's all shining on me, other times I can barely see, lately it appears to me, what a long, strange trip its been."

Offline calj737

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Re: Engine rebuild problems?
« Reply #6 on: August 13, 2014, 08:26:48 am »
and when you proceed to assembling the top end, heres a great resource for you:

http://forums.sohc4.net/index.php?topic=107040.0

'74 550 Build http://forums.sohc4.net/index.php?topic=126401.0
'73 500 Build http://forums.sohc4.net/index.php?topic=132935.0

*** Currently experiencing life at 60 WTFs per hour ***
I always thought getting old would take longer

Offline MCRider

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Re: Engine rebuild problems?
« Reply #7 on: August 13, 2014, 08:29:52 am »
and when you proceed to assembling the top end, heres a great resource for you:

http://forums.sohc4.net/index.php?topic=107040.0

Yup!
Ride Safe:
Ron
1988 NT650 HawkGT;  1978 CB400 Hawk;  1975 CB750F -Free Bird; 1968 CB77 Super Hawk -Ticker;  Phaedrus 1972 CB750K2- Build Thread
"Sometimes the light's all shining on me, other times I can barely see, lately it appears to me, what a long, strange trip its been."

Offline RayT

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Re: Engine rebuild problems?
« Reply #8 on: August 13, 2014, 08:41:23 am »
Thanks for the update guys.

Yes ill pull it apart agian to be on the safe side.

Offline MCRider

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Re: Engine rebuild problems?
« Reply #9 on: August 13, 2014, 08:46:38 am »
If you applied sealer up to the bearing shells, it could have squeezed over into the bearing. You should stop with the sealer right after surrounding the mainbearing bolt hole, allowing for it to squeeeze towards the bearing without getting in the bearing. Use a Q-Tip. Let tthe sealer set up for 5 min to minimize squeezing.
Ride Safe:
Ron
1988 NT650 HawkGT;  1978 CB400 Hawk;  1975 CB750F -Free Bird; 1968 CB77 Super Hawk -Ticker;  Phaedrus 1972 CB750K2- Build Thread
"Sometimes the light's all shining on me, other times I can barely see, lately it appears to me, what a long, strange trip its been."

Offline 70CB750

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Re: Engine rebuild problems?
« Reply #10 on: August 13, 2014, 09:34:35 am »
When my half rebuild engine would not turn over, usually the cam chain was binding on the lower sprocket.

If that's not the problem, I would think an oil ring is the culprit.

Edit:  my bad, barrel means cylinders, right?
barrel = cylinder

Gads I hope he's not turning it with a bar against the cam chain, though that's possible. Damage done.

I know that word, just reading quickly missed it  ;D

https://www.youtube.com/watch?v=xnGEX72AToU



Offline MCRider

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Re: Engine rebuild problems?
« Reply #11 on: August 13, 2014, 09:38:24 am »
I thought so.   :D
Ride Safe:
Ron
1988 NT650 HawkGT;  1978 CB400 Hawk;  1975 CB750F -Free Bird; 1968 CB77 Super Hawk -Ticker;  Phaedrus 1972 CB750K2- Build Thread
"Sometimes the light's all shining on me, other times I can barely see, lately it appears to me, what a long, strange trip its been."

 

;
Honda