452 replies to this topic

[JonnyAlpha]

 

1. Do I need to put assembly lube under the bearing shells, I am assuming not?

Between bearing and cap/block? No.

2. One of the holes in the bearing shell is offset to the hole underneath in the lower main bearing cup, I believe its on the flywheel end - see pic below.

Pretty standard.  You could widen the hole in the clock to match the bearing and in an highly tuned motor this would be advisable.  For a good road motor I think you have enough free passage.

3. One of the oil holes in the centre main bearing lower cup has what looks like a brass insert, the rest do not?

Normal - leave it be.

4. Do I need to lube the thrust washers?

Yes

5. End float is 6 thou so what thrust washers do i need, +3 thou oversize, as this would bring the end float down to 3 thou?

6 thou with standard thrusts in?  If so then yes, get a +3 thou set and re-measure it you are aiming for 3 thou endfloat - note you may only need half the +3 thou set (ie on one side of the crank only).

 

 

Thanks for the responses. 

Ref the Thrust Washers, I am not sure if these are standard so I guess I should measure them - what size are the standard washers?

Hadn't even thought about using half a set, I assumed that if you bought a +3 thou set each washers would have been +1.5 thou?

[GraemeC]

What thrusts are you using to measure the endfloat? They are normally stamped on the back, but I’m presuming they’re not new and hence could be worn.
In which case buy a set of new ones and measure again, or measure what you have and compare to the thickness of std ones (I don’t know what this is, but AC probably will).

[JonnyAlpha]

You can relieve the shell to bring it into alignment with a small file and extreme care so you dont bend the shell. Whenever I've built a mini engine (2x 998 ministox engines) I've always done this and the engines haven't let the driver down.

 

So a round needle file to ovalise the hole in the bearing?

[DeadSquare]

 

You can relieve the shell to bring it into alignment with a small file and extreme care so you dont bend the shell. Whenever I've built a mini engine (2x 998 ministox engines) I've always done this and the engines haven't let the driver down.

 

So a round needle file to ovalise the hole in the bearing?

 

 

If you look at the oil ways in the crank, they are countersunk.  I put a countersink in an electric drill, and from underneath, pushing upwards so that the swarf doesn't fall into the block, countersink the offending oil ways in the block;  a lot easier than a needle file ovalising holes in a bearing shell.

[gazza82]

Oil is under pressure so it will get to the bearing shells without tampering with them ... I think every A-series is exactly the same ..

[mini13]

If tis fairly standard I'd leave the oilways alone, if your building a trackday screamer then i'd chamfer/file them a bit to align them.

 

in terms of lube, alweays lube any sliding face with assy lube exept the rings whic i would do with oil, although some ring manufacturers give other instructions whoch you should follow, ie IIRC total seal say wd40.

 

for berting to block/rod faces i always put a bit of somthing there to prevent rust, a wipe of oil, even wd40.

[Cooperman]

That oilway will be fine.

[JonnyAlpha]

OK next up - checking the Deck Height.

 

So I put one piston onto Conrod No 1 using a linished down Gudgeon Pin.

 

 

And cut of some perspex pipe and fitted it over the bolt ends.

 

 

But I could not work out which way around they should go - is this correct?

 

 

After getting the Piston to TDC, I used two methods, first of all I used a steel ruler held on its side and a feeler gauge and then a DTI gauge:

 

 

After placing the DTI gauge on the block and setting it to zero, I carefully undid the magnet and slid the mount around so that the needle dropped onto the piston crown.

 

 

With both the feeler gauge method and the DTI gauge the piston measured 0.0175" down the block. When using the DTO gauge I gently rotated the crank slightly to ensure that piston was at its maximum height.

 

So 12.5 thou to come off of the deck, to give me a deck height of 5 thou or 15.5 thou to flush the pistons, for an extra couple of HP?

 

Does it matter which way you spin the Crank?

Edited by JonnyAlpha, 01 October 2019 - 08:27 PM.

[grizzler73]

What CR are you aiming at? Check the chamber volume,Do those calculations before any skimming.

[GraemeC]

You need to check all 4 and mark which rod and which piston was used in each bore. The next one may only be 0.009” down the bore so if you take your 12.5 thou off it would end up protruding.

[JonnyAlpha]

You need to check all 4 and mark which rod and which piston was used in each bore. The next one may only be 0.009” down the bore so if you take your 12.5 thou off it would end up protruding.

Sorry yes I had planned on all four, only managed one last night though.

[JonnyAlpha]

What CR are you aiming at? Check the chamber volume,Do those calculations before any skimming.

 

9.75

 

Already worked this out with a 5 thou deck height I need around 25cc (maybe less as the calculator does not allow for ring landing) in the chamber (currently 21.4 ish).

 

CR Calculator

[DeadSquare]

 

You need to check all 4 and mark which rod and which piston was used in each bore. The next one may only be 0.009” down the bore so if you take your 12.5 thou off it would end up protruding.

Sorry yes I had planned on all four, only managed one last night though.

 

 

If there is a difference, you will have to have a "step" on the surface of the block.

 

Wouldn't it be easier to work out the different piston heights and make an allowance by how much is polished from the corresponding combustion chamber to compensate the compression volume ?.

[mini13]

Eh? for that to work the head would have to be in 4 bits so it could sit at different heights for each cylinder.

 

Obviosly what needs to happen is to check all 4 in one cylinder, then swap the pistons around to even up the heights, then try them in all the cylinders and asign them so they all sit closest to the same height, then deck it accourdingly.

[Dusky]

Well to get it perfect you deck it to the height of the lowest piston, then machine the pistons accordingly.