Engine difficult to turn

[peterheywood52573]

As I rebuild the engine, it becomes more and more difficult to turn over. I have a socket and wrench on the crankshaft bolt. The rope seal was the most significant drag but now as I add pistons with new rings it gets concerning. I am wondering whether I should take it apart again. Anyone got experience, reassuring or otherwise?
Peter

[piman]

Hello Peter,

yes the engine will get harder to turn as more components are added. The difficulty is the very subjective amount of force required, which is difficult to assess by correspondence.

Did you size the rope seal when you installed it and also lubricate with oil?
Was the engine rebored and pistons supplied by the machine shop or is it a replacement of the rings only? (I suspect the former)
Was the crank easy to turn before fitting the rope seal, it should take very little effort to turn it (I know subjective again) with no seal, but I don't think the seal should really add a lot of drag?.

I would suggest basically doing a check of each of the steps you took on assembly by removing all the pistons and rods, remove the rope seal (My engine is an early one with a scroll seal so I'm not sure if you have to remove the crank to remove the rope seal?) then tighten each main in turn checking for rotational drag. This eliminates the crank bearings. Replace the rope seal. and check for rotation.
Fit each connecting rod, one at atime,to it's journal and check for fit. If that is good as I'm fairly sure it will be. Re install the pistons in the block.
Basically what I'm suggesting is a double check on all bearings and if that is good the engine is as it should be. There certainly is some drag with new pistons in fresh bores but it should rotate smoothly. Plenty of oil as you go by the way.

Let me know how you get on or if you have any other queries?

Alec

[peterheywood52573]

Thanks Alex,
I measured the torque to rotate at around 60Nm. I might continue to do that as parts are removed.
I did size the rope seal but have sent the tool back to Ken Jenkins. I guess that could be the problem. I did not want to remove the actual seal again.
The engine had been done about 20k ago, with .020 oversize bores and pistons. There is very little wear. I did replace the rings. Concerning is that the top 2 new rings require a lot of compression. In free state the gap must have been 10 to 15mm. I'll check these.
I had intended to put it all together and hope it bedded in. Thanks for the nudge to retrace a few steps. It is a pain but it will never be easier.
Peter

[piman]

Hello Peter,

try giving the seal a good spray with WD40 and see if that helps.

Unfortunately I don't think in metric as far a torque goes, I'll have to have a look to see what that is in Imperial.
As long as the ring gaps are correct there is little else that can be done there. However just slackening off the big ends by several turns, one at a time could be quicker and easier than removing them as I suggested. If there is a tight bearing (e.g. having installed a cap the wrong way round?) that will show up. and also give a good idea if it is the crank, although pistons do add quite a bit of drag.

Alec

[peterheywood52573]

The 60Nm (44lb Ft) was without tightening the main brgs. Removing the 6 pistons dropped the torque to 12Nm (9 lb ft). All pistons were equally draggy. Like you say Alex, there's not much that can be done. Quite a lot of power must go missing but there's plenty of metal around to keep it cool while it beds in.
More concerning is the 12Nm in the seal. We don't want either the seal or the oil being burnt. I think I'll take this apart. Maybe I did not trim the seal properly.
As for the main brgs, maybe I should tighten them more progressively whilst turning the crank? At least I will know there is nothing obviously stupid.
Peter

[piman]

Hello Peter,

it's a very long time since I re built a rope seal engine and cannot comment on the torque to turn it against the seal. If you haven't already removed it I would suggest ringing Ken Jenkins for his advice?

Alec

[piman]

Hello Peter,
how did you get on, the reason I ask is that I have just installed the crank and pistons into my engine, but this is a scroll seal early engine.
All new pistons and bearings and it turns overquite easily. As each piston went in it got progressively harder to turn but when all six were in it is not what I call stiff?

Alec

[peterheywood52573]

Thanks for asking Alex.
I have stopped thinking about it, to be honest. I became more concerned about the pistons than the rope seal. I was going to try different piston rings but Robey supply the same rings as SNGB. The engine seemed to free-up a bit, with a bit of Redex in the cylinders. Yesterday I was torqueing-down the flywheel bolts (65lbf ft) and the engine would turn. It seemed reasonably smooth, though.
What piston rings have you installed ? Mine are Grant (USA).
Dinner is ready, must go.
Peter

[piman]

Hello Peter,

I don't know the make of the rings. I had new pistons supplied by the company that did the engine machining. I didn't really notice the make and I've binned the box they came in.

Alec