Building a new engine

[Muppet]

for rings a diamond files betta if ya got one

[rosscla]

Yes, inside micrometer (or bore gauges and an outside micrometer or good vernier) would be accurate but making those measurements accurately depends greatly on experience and good technique with the tools.

For most purposes in a home workshop the feeler method will probably be close enough.

[Snails]

Thanks. I'll see what a feeler gauge tells me but get it checked properly anyway.

I've now assembled it enough to allow me to try and measure my port timings. I'm using a timing disk to do so but I get different readings depending on which way I turn the crank. Am I correct in assuming that this is because you can tell exactly where the bottom and top of the cranks movement is, and that I should take the average of the two?

Before assembly I measured my timings using a piece of card down the barrel so here are all of what I think my timings are. They are listed in order A. Card. B Timing Disc Reading 1 C. Timing disc reading 2 and D. Average of the two timing disc readings

Transfer's A - 123 B - 132 C - 122 D - 127
Exhaust A - 160 B - 168 C - 162 D - 165
Inlet A- 142 B - 146 C - 153 D - 149.5

So quite a large difference between the readings with the card in the barrel and using the timing disk. Also the inlet timing seems better than expected from reading what this article says

http://www.lambrettaspares.com/info/lam ... rs+45.html

[Snails]

I've now assembled it enough to allow me to try and measure my port timings. I'm using a timing disk to do so but I get different readings depending on which way I turn the crank. Am I correct in assuming that this is because you can tell exactly where the bottom and top of the cranks movement is, and that I should take the average of the two?

Anyone prepared to comment on whether I am have this right?

[rosscla]

Timing disks need to be quite large to read accurately, it's generally much more reliable and repeatable to take the measurement of the port heights, deck height and stroke and put those into one of the online calculators. The measurements you made with the card with the barrel off assume the deck height is 0. Is this in fact the case now it's is assembled??

The dwell at TDC and BDC can lead to slightly misleading readings. Ideally marking these you need to find the point midway between the points where you can detect the piston moving again this is easier with a dial gauge.

[Snails]

Actually I think the assumed deck height was actually 1 but if I'm honest I'm not even exactly sure what deck height is and how it can be measured?

I should also check my head squish at this point too shouldn't I, so i will do that next time I get out in the garage.

[rosscla]

Deck height is the difference between the gasket face of the barrel and the edge of the crown of the piston.

If it is level it is 0

If it is below it is -

If it is out the top it is +

[Snails]

Ah I see, well I assumed -1 in that case but I will check it now that its possible

[Snails]

So I measured the squish with the engine together, and it was massive - over two mil with no head gasket. I've therefore lapped the cylinder head until its now 1,45 but still without a gasket. I'm pretty sure I've read that some people don't use a head gasket? Could I just use welseal instead?

The reason I ask is that if I add the gasket its back up to about 2mm and I'm not sure there is enough of the mating surface of the head to take another .5 off.

[B-Race Tuning]

As long as your mating surfaces are good (which, after lapping over 0.5 mm off they should be perfect), then no gasket required and a very light application of loctite will suffice. When measuring with a degree disc your exhaust and inlet (and transfers, but less visible to be as accurate) open and close at the same btdc as atdc. if those then read the same, then you'll know your tdc, dead centre of dwell
Edit: Wellseal doesn't properly "set" so effectively for use on a two-stroke head.