One for the engine rebuilders........

[berni29]

Hi There

I am just starting to put back my twincam engine again. In previous threads I have found out is a late 701M block with an early head. It is supposedly rebuilt (a longggg time ago) and just ready to put back together.

Following the Miles Wilkins book, I have the jackshaft in, and all well and good there. Turns freely with the resistance you would expect from engine assembly lube.

The crankshaft which has +0.30 bearings I measured with a green plastigauge. All the readings were wider than the widest end of the scale (tight) and my spider senses started to tingle.

I then reassembled with the assembly goop (red), plus some very thick old engine assembly grease. At 20ft lbs, and 40ft lbs the engine was rotateable by hand just by gripping the front small crankshaft sprocket (using a cloth), although it took a bit of an effort to actually start the rotation.

At 55ft lbs the crankshaft appeared to have bound up, but actually with a bit of leverage against it it will free itself and thereafter still rotate freely using one hand gripping the sprocket. However if you leave the engine 5 minutes it will not turn with the force of my hand even if I push against the counterweights. However, with a bit of leverage it starts moving and then is rotatable by hand again. and so the cycle repeats.

Is this an expected behaviour and perhaps a function of the assembly grease, or is in fact the crankshaft too tight and requires further investigation? Both standard thrust washers are in.

Many thanks in advance!

Berni

[Quart Meg Miles]

Hi Berni,

I'd get rid of any grease on rotating bearings and use Graphene or just engine oil. If you fill your filter with oil before fitting it and spin the engine without plugs before starting up the surfaces will be fine. Thrust washers should leave around 0.005" total clearance and shouldn't cause any drag.

I assume the 501 has a six bearing crank so you aren't fighting rope seals..

[Billmack]

Too tight. Something needs machining. Pull caps and look for shiny spots on the shells. That would indicate they're rubbing. Do they all squeeze the plastiguage down that much??

[rgh0]

Hi Berni

Your clearances appear to be less than 0,001 inch from the plastiguage versus a specification range of 0.0015 to 0.003 inch so it does not surprise me that the crank does not turn freely when tightended down. How straight the crank and crank main bearing tunnel is can also be influencing this as well ac acual journal diameter.

As a start I would carefully measure up each journal with an accurate micrometer to check diameter and roundness versus a +30 thou bearing specification to see where the issue lies.

Depending on that outcome you may need to get the tunnel bore and crank straightness checked.

cheers
Rohan

[tonyabacus]

Hi Berni
Do you know if the crank and the block have run together previously or are they parts brought together for the rebuild. If the latter it may be possible that one or the other has a small distortion and therefore need checking as Rohan has suggested. Are the main caps original to the block and is each one married to its partner in the block the correct way round.

Many years ago I had an AX block which had a similar problem and it turned out to be a minor distortion on one of the centre mains.
Tony

[2cams70]

I'd suggest backing off the bolts on each bearing cap in turn in order to identify if there is any particular one or two that is the cause of the problem. If the crank rotates freely when a particular cap is backed off you know where to investigate further.

In my build I had a similar problem that I traced back to a small 3mm long brush bristle that had landed on a shell before the crankshaft was installed. The origin of this was from the application brush in the lid of the ARP bolt assembly lube. I'd used some assembly lube for the main cap bolts and unbeknown to me a small bristle had fallen from the lid. It doesn't take much to cause a bind. A hair bristle was enough to cause a bind in my case even with 0.002 to 0.0025 bearing clearance!

If you think your bearing clearances may be too small I'd suggest confirming the suspicion by accurately measuring the bearing journals and tunnels with a micrometer and not just relying on Plastiguage.

[berni29]

Hi Guys

Thank you all for your insights and suggestions. I will investigate further and report back!

Berni

[berni29]

Hi Guys

Well I cleaned and reassembled, using only the red goop this time. Just as I finished my new assembly lube arrived. I didn't think it was arriving today.

So the result is that the crankshaft is still quite difficult to turn from a stationary position, but better than it was with the previously added assembly grease. Once it does rotate I can do this with one finger. Please see video link below........

https://www.wefm.co.uk/lotus/lotusengturn.mp4

Would you say that if I can do this then the clearances cannot be dangerously tight?

I am looking to find a reasonably priced accurate secondhand micrometer and bore measuring tool, but that could take a while.

In a perfect world I would take the engine to my local trusted, experienced, reasonably priced Lotus engine builder and let him check it, or even do the building up for me. But I don't have one or the funds for.......

So at the moment I am left with what I have in front of me and am experiencing using my senses.

Many thanks for your informed opinions!

Berni

[Donels]

I had a similar problem on a cross flow rebuild and did what 2cams is recommending. Turned out to be the centre bearing which was too tight. Have you tried that?

Also have no idea what ‘red goop’ is but sounds like you have made an improvement by removing the thick stuff, so why not try just using engine oil. If it turns easily you may be ok. You can always reassemble with red goop. Currently you don’t know if it’s a clearance issue or a goop friction issue. I always use Graphogen for assembly.

[promotor]

Hi Guys

Well I cleaned and reassembled, using only the red goop this time. Just as I finished my new assembly lube arrived. I didn't think it was arriving today.

So the result is that the crankshaft is still quite difficult to turn from a stationary position, but better than it was with the previously added assembly grease. Once it does rotate I can do this with one finger. Please see video link below........

https://www.wefm.co.uk/lotus/lotusengturn.mp4

Would you say that if I can do this then the clearances cannot be dangerously tight?

I am looking to find a reasonably priced accurate secondhand micrometer and bore measuring tool, but that could take a while.

In a perfect world I would take the engine to my local trusted, experienced, reasonably priced Lotus engine builder and let him check it, or even do the building up for me. But I don't have one or the funds for.......

So at the moment I am left with what I have in front of me and am experiencing using my senses.

Many thanks for your informed opinions!

Berni

You should be able to rotate the crank by just holding the crank nose with your hand, if you struggle to get it moving by hand grip it's too tight. Are all the mains caps definitely in the right positions? Numbers 1 and 3 are definitely right but are the rest?
Have you checked to see if your bearings are showing signs of pinching as that should point you to which bearing(s) is/are problematic and if it is in a small spot, or over the whole of the bearing surface?
If I found this issue I would check : crank sizes, main bearing bore diameters, and bearing thickness from the back of the shell to the contact surface (although you need a micrometer with at least one rounded anvil to measure bearing shells). Hopefully you'll find the answer while checking those three things.

[tonyabacus]

Promoter is spot on, the bearing shells will tell you if there is a problem. As you have had the caps and crank out a couple of times by the sound of it, it may be more difficult to spot which marks are responsible for the tightness.

. The solution to this is to buy some engineers blue, which once all the bearing shells are clean (that includes their retaining surfaces in the block and caps, smear a very light coating on each shell, don’t oil them, replace the crank and caps with care, tighten down lightly just short of full torque and spin the crank.

Where it is binding will show up in the engineers blue. At this point you may then need to follow the remainder of Promoter’s recommendations

[rgh0]

The plasti gauge measurements and stick / slip behaviour all say one or more of the bearings are slightly tight.

Just need to find out which bearings and why.

marks on the shells can help
loosening one bearing at a time can help
measuring up in detail the crank , bearings and bearing crush of the main caps can help

once you have done all of that a decision can be made on how to rectify or whether you accept the issue as is or whether further checking of crank straightness or block bore straightness is required

cheers
Rohan.