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renovated engine burning oil  Rating:  Rating
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 Posted: 04-27-2015 05:39 pm
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Jensenman
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Your description of the smoking problem does indicate a ring, rather than a valve guide, problem. I once disassembled a Ford 2.3 which had the same complaint, on that one it turned out whoever replaced the pistons and rings snipped the end off of the 'expander' for the oil ring. If that is done, the 'rails' won't seal correctly.

If I recall correctly, somewhere along the line there were shims available to adjust the liner nip. None of the usual suppliers seem to list them, but there's a Waukesha industrial engine which shares the 3.75 bore size and liner shims are available for it. http://www.powermaxparts.com/DEMO/WA-265-A.html

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 Posted: 04-27-2015 08:32 pm
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Esprit2
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I don't recall any liner shims, but then there were a few J-H parts that never made it to the Lotus world. But if the shims are available, I'm working on an engine that could use a little more 'nip'.

A shim 'donut' would have to slide on over the iron liner's spigot (the part that slips into the seat/bore in the block). The spigot's OD is:
101.360 - 101.384 mm (3.99055 - 3.9915") OD.

The shim's OD should be about equal to the liner body's OD, but I don't have a dimension for that, or a liner handy to measure.

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 Posted: 04-27-2015 09:33 pm
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Esprit2
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I lied, I do have a liner handy and it's OD at the step/ seat is:
4.294" (109 mm).

So a liner shim would need to be something like:
ID: 4.000" (101.6 mm) -0.000" / +0.???"
OD: 4.290" (109.0 mm -0.???" / +0.000"

Just laser cut a few out of stainless shim stock.

Last edited on 04-27-2015 10:13 pm by Esprit2

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 Posted: 01-15-2017 09:53 pm
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DonBurns
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I was looking for an answer to another question and noticed this discussion about liner nip, so thought I would add this recent experience. The machine shop had my block on the grinder and I mentioned the specification to the liner nip. Of course when I came back to look at the progress I saw that they had decked the block and liners flat - no nip. This lead to an argument about the need for a nip but I held my ground and insisted they fix it. They ended up spending quite a few hours (they say) programing their NC mill to grind the block down from the liners by the required nip. (Well - actually .003, but at some point you just give up).

So it sounds like shimming the liners up is the way people usually go, but is there any reason why milling the block down should be an issue?

My question, since I see valve clearances were also discussed in this string - I have a 2.2 liter, 104 / 107 cam combination and 9.6 compression. Are the valve clearances the same for any cam? So .006 In / .011 Ex regardless of cam?

Thanks-

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 Posted: 01-16-2017 05:03 am
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Esprit2
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DonBurns wrote:
So it sounds like shimming the liners up is the way people usually go, but is there any reason why milling the block down should be an issue?Anything that reduces the distance between the crank and the cams (milling the head, decking the block, etc) introduces that same amount of extra slack into the timing belt. By definition the cams are timed with the crank at TDC, and the crank cannot be allowed to drift off TDC. So as the tensioner pulls the new slack out of the run of belt between the crank and the exhaust cam pulley, it must draw it up and over the cam pulleys. That turns both pulleys counter clockwise, retarding the timing. How much? It depends upon how much the parts were machined; but something less that a full tooth pitch, so you can't do anything about it with stock parts. Aftermarket adjustable pulleys would be required in order to zero in on perfect timing. IMHO, that's worth it for a racing engine, but not for the street.

On the other hand, Lotus introduced the current composite head gasket in Jan 1993. It's compressed thickness is about 0.5mm / 0.020" thicker than the original steel-asbestos-steel gasket, so it lifts the head that much higher off the block deck. Besides 'advancing' the cams a bit, raising the head also increases the combustion chamber volume, and reduces the compression ratio by about half a point... 8.4:1 becomes 7.9:1.

When the new gasket was introduced, Lotus revised the machining on all new 910 & 912 engines (the 907 was long out of production), cutting the block deck that much lower, and seating the liners a like amount deeper to preserve the Nip. So engines built since Jan '93 have the correct compression with the new gasket, and all older engines have 0.5:1 less compression that they started with.

If you're ever faced with decking the block a few thousandths for whatever reason, consider taking the full 0.5mm / 0.020", just to get your compression back.

Alternatively, if you ever buy new pistons, order half a point more compression that you really want.
DonBurns wrote:
I have a 2.2 liter, 104 / 107 cam combination and 9.6 compression. Are the valve clearances the same for any cam? So .006 In / .011 Ex regardless of cam?The 104 and 107 cams both use the same valve clearances:
0.005 - 0.007 Intake
0.010 - 0.012 Exhaust

If you converted a 907 to 2.2 and are using the stock 907 head with the 104 & 107 cams, the stock valve springs will go coil bound due to the extra lift. The 910 & 912 heads are built from the start to work with the high lift cams.

For a 907 head, there are special thin-wire springs available from Dave Bean Engineering, and probably some of the other USA Lotus specialists, like JAE. I don't know if Delta carries them; but they sell the cams, so they might have the springs to go with them.

In the UK, it seems more common to machine the valve pockets in the head a little deeper to allow for the extra lift. Either method will work... just be sure that you do 'something' to allow for the lift. If you don't, something is going to break the instant you try to start the engine.

Regards,
Tim Engel

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 Posted: 01-16-2017 03:31 pm
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DonBurns
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Tim-

Thanks for the feedback. I did fit the "competition valve springs" that are sold specifically for use with 104 and 107 cams. The club store mentions they are necessary to avoid valve float (bounce?) but no mention of the binding issue, but I have to assume the springs are correct - the engine did not break when started anyway. I also fitted "big valves" , 1.450" Intake and 1.275" exhaust, and the upgraded studs to allow the newer torque specs, and new JE 9.5:1 pistons. I wonder if the final compression of 9.6 is due to the decking work.

I had not thought of the valve timing changing due to decking the block. I always thought decking was a standard part of any rebuild. When I have a moment I will do the math and calculate the degrees of cam shift that would go with the .1 compression increase. Although there are other factors going on, like CC'ing of the head and thicker head gasket, so I'll just calculate cam turn per mil.

I have another concern at the moment. The builder did so many things wrong besides decking the liners flush (no thermostat, no oil in the transmission and several more minor issues) that now I'm wondering if they put the cams in the right place. I told them (but I told them about the nip as well) and the boxes were marked, but... Anyway I was going to check the lift yesterday and took off the intake cover and was setting up my dial gauge, but realized mine is only a .25 maximum gauge. I think that should work as a way to verify once I get the correct gauge.

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 Posted: 01-16-2017 10:21 pm
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Esprit2
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DonBurns wrote:
The club store mentions they are necessary to avoid valve float (bounce?) but no mention of the binding issue, but I have to assume the springs are correct.Hmmm... the stock valve springs will rev beyond the stock tappets' and rods' max rev limits, so I don't see higher as being an issue. But that's picking nits... the real point is that the upgraded valve springs are also necessary to avoid going coil bound-with the high lift cams. You've covered that base.

DonBurns wrote:
I wonder if the final compression of 9.6 is due to the decking work.It's like touching a spider web... everything affects everything. The compression ratio will vary with all those things, and I can't tell you from here what is dominating in your engine. If you really want to know, then CC the combustion chambers, and add the incremental volume of the thicker gasket.

DonBurns wrote:
now I'm wondering if they put the cams in the right place.Are the cam's "Lotus" OEM, or regrinds? Lotus marked the cam's exposed shank... the part visible between the back of the pulley and the front of the cam carrier/ seal. The 104 cam will have a string of 444444444...s stamped around the shank, and the 107 will have 7777777...s. If they're regrinds, then you're at the mercy of whomever reground them... did they re-mark the cams in any way? Usually not. Failing that, the lift is the easiest to measure identifying trait... you're on the right track.

C-cam = No grove/ no marking.
D-cam = One grove.
E-cam = Two grooves cut around the shank.
104 cam = 444444444444....
107 cam = 777777777777....
The part number cast into the camshaft is for the raw blank, not the ground cam. It's the same for all.

Regards,
Tim Engel

Last edited on 01-16-2017 10:22 pm by Esprit2

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