Engine rebuild question ..

[Hilly_70]

Rebuilding an engine and I have just had the casing to the engineering place along with the crank for align bore and thrust cut for the new bearings..

I am using a combination of the HP255 Rebuilding your engine book and the bentley manuals for reference

When I have got it home I have done a test fitting of the 2 case halfs with the new bearings and the crank (No rods just bare crank with flywheel temp fitted) .. All bearings cleaned and oiled thoroughly before assembly.

My question is this ..

When the case half are together, Im not confident on the amount of resistance to turn the crank from the flywheel there should be.

I can turn it reasonably freely although there is a slight initial resistance and I can spin the flywheel and let it go and it will turn approx another 180 degrees through its own inertia.

Im convincing myself its a little tight .. but need a second opinion .. or third!

Is is just the newness of the bearings? it does feel less resistant the more I move it..

Thoughts appreciated chaps!

Hilly

 

[K@rlos]

There should be no resistance or tight spots. What brand bearings?? I’ve ran into issues with Mahles not fitting nicely and nipping the crank journals but silver lines have always come out good. Have you used a plasti-gauge to check tolerance of them?

 

[Hilly_70]

Silverlines .. not used a plastiguage yet .. I've ordered some but never used it so need to learn that bit!

It's not got any tight spots .. but just feels a little resistive in its full turn .. if I break the case a few mm then it frees off a little ..

I've got a video I will try and post ..

Thanks for the help

 

[K@rlos]

Check your bearing clearances. You should be able to spin it over with your littlefinger when the case is closed up.

 

[atafonso]

Check your bearing clearances. You should be able to spin it over with your littlefinger when the case is closed up.

Exactly, check the bores on the case as well for the line boring could be done slightly tight.
Abel

 

[Hilly_70]

Thanks guys ..

Ive checked with plastigage on number 2 bearing (as its the split one) and clearance is 0.002 in ..

I can't turn it with my little finger, its not quite that free .. bearings click into the case ok without much force..

The engineering place took 9 months just to get it done in the first place so didnt fancy taking it back for another 9!

Any suggestions? .. bearing clearance seems in spec with the Bentley manual..

How can I check if the case bore is too tight?

Thanks

Hilly

 

[Hilly_70]

Just uploaded a video to demonstrate how free / tight the crank is :

https://www.youtube.com/watch?v=2JEMPnsmi0w

Thoughts appreciated

 

[atafonso]

You can determine what saddle is tight by loosening both nuts of one saddle at the time and rotating the crank.

It could also be the one or more dowels are too high, you can check that by reopening the cases and then looking for a high spot in the bearing, it will be sniny exactly where the dowel is located.

Has your crank been reground? Measure the journals with a micrometer as they can be the problem too. Have you checked if the crank is straight? Put the n1 and n4 bearings, then check the runout on n.2 journal using a dial gauge with only one half of the cases and the bearings fully seated on the saddles.

Whats that on the flywheel? It looks like it's woblying on the video?

If you stuck still, come to me i can do it together with you and help you out for free.

Abel

 

[Hilly_70]

Thanks for the info Abel .. much appreciated.
The flywheel is just on loose to turn it so the wobble is just cos it's not tight .. I have no shims in there at the moment either.

I tried it without the dowels in too and it was the same.

Cranks not been reground, just used same same inner main bearings as was in before .. just larger outer for the align..

I try the crank test next with the dial gauge..

Thanks for your offer .. it's much appreciated dude ..

Hilly

 

[atafonso]

If the crank is Std, chances are the line boring is too tight.

Try placing the bearings in the case, then torque it together without the crank, then use a flashlight to try and find out if there is a gap between the halves. If there is, then the line boring is tight.

You can do the same test without the bearings too to identify if the case is not spread, that happens when the engine had overheated badly or abused.

I can give you my number if you want, then we can talk through WhatsApp for a quick reply.

Abel

 

[Hilly_70]

Cheers Abel ..

I put the cases together and even used plastigage in between the case halfs next to the bearings and saw no light through the crank gaps and the plastigage went down to 0.002 so I dont think it is the line bore thats out ..

I also found this :

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

I think this is the issue .. how I now rectify without replacing it or the bearings im not sure yet .. My next step is to check it for round with the micrometer to see if its out of round or crank run out..

I guess this is the learning curve of building an engine though!

... at least I have all winter.

Hilly

 

[K@rlos]

Yeah that’s too tight. If Abel is offering to help then I’d take it to him and avoid pontental problems later on. Be sure to get him a good drink too

 

[Hilly_70]

I may have to bud .. Don't worry .. I'll deffo look after him for the assistance

 

[atafonso]

Yeah that’s too tight. If Abel is offering to help then I’d take it to him and avoid pontental problems later on. Be sure to get him a good drink too

Only a good cup of coffee is enough payment :lol: :mrgreen:

Abel

 

[atafonso]

Cheers Abel ..

I put the cases together and even used plastigage in between the case halfs next to the bearings and saw no light through the crank gaps and the plastigage went down to 0.002 so I dont think it is the line bore thats out ..

I also found this :

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

I think this is the issue .. how I now rectify without replacing it or the bearings im not sure yet .. My next step is to check it for round with the micrometer to see if its out of round or crank run out..

I guess this is the learning curve of building an engine though!

... at least I have all winter.

Hilly

Yes, your crank is bent. To correct it needs regrinding. But before that, insert the flywheel and check for runout too. If too much, you might be better off getting another crank as the flywheel runout will make a vibration in the engine and also when pulling off with the clutch.

Abel

 

[Hilly_70]

Thanks Abel ..

Do I need to check for runout movement on the flywheel on the edge or front face or both? ..

I'll have a play in the garage and see what I get ..

Much appreciated bud ..

Hilly

 

[atafonso]

Thanks Abel ..

Do I need to check for runout movement on the flywheel on the edge or front face or both? ..

I'll have a play in the garage and see what I get ..

Much appreciated bud ..

Hilly

Even though the crank is bent by 0.10mm, it would be enough to make the flywheel wobble. At the crank snout, the bentness(if that word exists lol) will be really small, but it is amplified by the size of the flywheel. If you have say 0.02 or 0.03mm runout at the snout, you could easily end up with 0.30 or 0.40mm at the flywheel edge :shock:

Check the runout at the face where you bolt the clutch pressure plate, just above the holes

Keep us posted

Abel

 

[Hilly_70]

Will do bud .. thanks for the info ..

I'll check and report back

 

[Hilly_70]

Ok .. so I have approx 0.18mm run out from the clutch face of the flywheel...

https://youtu.be/fNUfRGAjmS8

Is it a replace crank kinda thing?

Or a crank grind? .. either way .. any budget conscious suggestions

Hilly

 

[atafonso]

You could use the crank if you had no other choice, but i wouldn’t. There will be vibration and the life of your case will be reduced considerably. The main problem is that the flywheel shims will not be perfectly seated on the flywheel snout, so the n.1 bearing will wear quicker.
For the price of regrind plus the above, i would just buy another crank. You can get a good used crank that might just need a polish for less than the regrind price.

Abel