Update: Clay test and Measuring Valve MOP

[512BB]

'The exhaust/outlet sprocket usually has the letters EX engraved on it. On your photo I can see IN scratched on the sprocket on the inlet side so that is correct. I cannot see EX scratched/engraved on the other sprocket.'

In my experience, only the inlet camshaft sprocket was engraved by Lotus. Latter day owners and engine builders may have scratched EX on that particular sprocket, for more clarity when reassembling.

'Oddly enough I do not know how to distinguish the inlet cam from the outlet/exhaust cam; someone else will have to describe that.'

As 2cams says, the camshafts are identical, OR WERE, WHEN THEY WERE NEW, so long as they both have no rings, 1 ring, or 2 rings where the sprocket fits. I say when they were new because when they were new, there was no wear on the lobes, but after thousands of miles, the lobes have worn individually but not identically with their respective bucket and therefore the camshafts should not be moved from their original location.

Leslie

[dlb123]

I find it interesting also that your engine even with a new block has close to zero deck height. I've heard it is supposed to be about 0.020" below deck for a stock standard engine. My engine was the same as yours with close to zero deck clearance even with standard length 4.800" length conrods. Are your conrods standard 125E type? Many aftermarket conrods are 4.826" length.

.

I was being daft. I don't have 3-3.5 thou. I have 30-35 thou or 0.035" as per the photo of my digital vernier has now led me to realise Which seems to tally up with the fact that the block is brand new. Yes the conrods are the standard 125e type.

Thanks for the diagrams, they are superb. Picture says a thousand words. Looking at them, that suggests I am measuring the deck height from the correct place.

I will take the measurements you have set out. I'm actually using a large medical syringe i pilfered from my dad (doctor), which he assures me is accurate (one would hope so). Perhaps I'm being a cheapskate haha. But it's an effective tool.

I did make a little groove in the the Perspex to accodate the lip of the inlet valve. 2cams70, are you concerned about your valves sitting just proud of the face of the cyl head?

Best. Dave

[rgh0]

35 cc sounds about right for your quoted head thickness at 4.58 and a relatively standard valve location and unmodified combustion chamber. The inlet valves lips being a little above the head face are not a problem as long as you have adequate clearance with the pistons which it appears you have. Your compression ratio will be high at around 10.8:1 depending on the rest of your measurements and that will work OK on premium unleaded for road use.

cheers
Rohan

[2cams70]

I did make a little groove in the the Perspex to accodate the lip of the inlet valve. 2cams70, are you concerned about your valves sitting just proud of the face of the cyl head?

Best. Dave

No that's fine that it's sitting proud. There's no piston interference and the valve clearance shimming is correct. I've done the clay test on my engine too and there's plenty of clearance even with higher lift Q420 cams. All of the aftermarket pistons have deep valve pockets these days so you are very unlikely to get valve/piston interference if you are running original Lotus specification camshafts. In original specification the "Big Valve" engine only had small valve reliefs in the piston. Only when using these pistons would there be a possible concern.

[dlb123]

Another update.

Put the measurements and figures in to a compression ratio calculator. This is what I came out with. Quite a useful little website actually.

http://www.csgnetwork.com/compcalc.html

Coming out at roughly 9.7 : 1 with a standard gasket thickness as measured. That seems pretty good to me. And knowing that the valve to piston clearance is sufficient, I'm going to opt for a standard head gasket.

I heard of some people using wellseal with the copper gasket. Is this advisable with a new block/freshly machined head? It's not somthing I'd instinctively do.

Best,

Dave

[2cams70]

You don't really need an online "compression ratio calculator". In this case it's easy to just calculate it from first principles. All too often in my working life I see cases where people just grab things from websites, "plug in the numbers" and the results are incorrect because they haven't properly understood the "whys" of what they are doing. You never have that problem when you work from first principles. Use a calculator only once you understand the first principles.

How did you calculate the piston dome volume? I was going to show you how to do this using the measurement I said to gather previously.

By the way, 0.035" deck height is more than standard. Standard is supposed to be about 0.020". Being a new block your engine may be taller than standard due to machining allowance. Too much below deck height is not good for engine efficiency. Although it reduces compression ratio it also promotes knocking. You may wish to consider reducing the deck height to at least the standard 0.020" value. Racers usually run zero deck height because that's most efficient and it also the reason the 4.826" (0.026" more than standard) conrod length came into existence.

You don't need any "Gunk" on the cylinder head gasket.

[dlb123]

That's fair enough, I know I dont need a compression ratio calculator but it's useful. I understand the first principles, that we are looking at a ratio of min/max volume in the cylinder, I was just being lazy.

I calculated the piston cutout volume by measing the volume with piston intruder exactly 10mm below the deck, then using 'V = ? r 2 h' to calcute the volume of the 10mm segment, and subtract that from the observed total volume. Hence the piston dish is the difference (55cc-53.5cc), which was 1.5cc.

I digress. I pulled the timing cover off and resealed with 'wellseal', which was recommended by the local machine shop. For anyone who's used it, I was surprised at how runny it was. I wanted to double check that the oil feed to the camchain was not obstructed, even though I used it very sparingly in this area. My method was to attatch a small rubber hose to my compressor, and feed that through the oil jet such that it sealed. With a very low flow of compressed air, I can hear it escaping the oil galleries somewhere deep within the block, but can't see exactly where (any thoughts). Nonethless, Im satisfied that there is a clear passage for the oil once the engine is up and running.

I now have the head back on again, and have been examining the timing with a dial gauge/timing wheel. Seems as though the exhaust is retarded by about 2 degrees, and intake 4 degress. Take a look at the pic below, I've discovered a couple of small chips on the intake sprocket. They seem fairly inconsequential, and are not in contact with the chain. Should this be a worry?

Next step is to finally bolt down the head, once i find the correctly sized breather grommet. I found that the stock twin cam breather is too narrow for the new 701m block. Dont know why?

Thanks for all your inputs

Dave

[2cams70]

Do yourself a favour and use all new timing gears. They aren't that expensive. From what I can see of the gear on the crankshaft that looks worn too. The LTC engine is not the best design being only a single row chain so things wear fairly quickly relatively speaking. Most other engines with timing chains are double row for improved durability.

I take it you used a new timing chain as a matter or course? I'd highly recommend the adjustable sprockets from QED. They are reasonably priced and make the task of setting up the cams much easier. I take it also you checked to ensure the valve clearances were correct before timing the cams? You'll get an erroneous result if they aren't.

[dlb123]

Hello again.

Ordered some shiny new adjustable sprockets from QED. Looking forward to tinkering with them later on. The valve clearances were set by the machine shop when they built the head, but a preliminary check tells me they are way too tight, I have no idea why. So before I time the engine up, I'm going to have to reset the clearances. Yes I used a new timing chain.

I've got a couple of questions for the wise among us. With my new block, I received a small bag of widgets (plugs etc), and there appears to be a dowel pin (picture below). Whats it for?

Also, I've got a lower end gasket set which has this clear plastic washer. Any idea where this goes?

Thanks for your help.

Dave

[512BB]

The washer is for the sump plug. No idea where the pin goes, not on any twin cam that I own.

Post up some more pics of your block and head Dave, I would love to see. Who did the head work for you?

Leslie

[2cams70]

That pin is for the timing chain tensioner pad if the block is used in an OHV application. You don't use it on a Twin Cam