457 replies to this topic

[JonnyAlpha]

So after a delay (apparently due to telephone and internet issues), I have just received my +40 pistons.
I have measured them using a set of Clarke Digital Vernier Calipers 90 Degrees to the Gudgeon Pin at the base of the pistons skirt. According to my calipers the pistons are 71.55mm.





According to info on here a 1275 +40 is 71.65mm, that would suggest that the gap is 0.1mm, which according to an online conversion tool this is 0.0039" (nearly 4 thou).

The recommended gap is 0.0025 to 0.003.

As mentioned above my machinist went ahead and machined the bores before getting the +40 pistons, so if he has bored them to quoted figures the gap will be too large!!

Let's hope my machinist hasn't done so :-(

Edited by JonnyAlpha, 06 September 2019 - 08:46 AM.

[JonnyAlpha]

Just re-measured the pistons (after remembering to zero the callipers) and am now getting a reading of 71.57 / 71.58 which gives 2.7 - 3.1 thou which would be pretty much bang on. Obviously I need the machinist to measure and double check as I don't have anything like Mitutoyo quality gauges

[JonnyAlpha]

Ok so I took the newly +40 pistons to the machine shop, today and had a few jobs done.

Whilst there I asked the machinist to measure the bores and the pistons so I could see and confirm the gap.

 

He only measured one bore and one piston but the results were as follows:

 

Bore - 2.8205" 71.64mm

Piston - 2.8185" 71.59

Gap - 0.002"

 

When I mentioned that the gap I have been advised is 0.0025" - 0.003" he said that if it were his engine he'd be happy with it and that it was within the Nural recommended tolerances. 

He said it could be increased by 0.0005" (if thats how you write 1/2 thou), but would be at my risk.

 

I have asked for advice on this on this thread.

 

He pressed off my old pistons, and ran the block and my rods through the engine wash, so I am nearly ready to start the trial build.

Whilst at the machine shop we appear to have misplaced a rod nut, not really a problem as I have decided to get some ARP ones but I do need it for the trial build.

 

When I next get some time in the garage, I am going to clean you the Con Rods.  

 

I still need to get some Piston Ring Pliers and need some linished down gudgeon pins so I can slip the pistons on and off.

 

Here's the block going in the parts washer:

 

[DeadSquare]

It might be cheaper to buy 13/16" bright mild steel than buy linished pins.

 

It is usually .about 001" undersize.

 

 

 

  

 

 

 

 

Edited by DeadSquare, 10 September 2019 - 10:41 AM.

[JonnyAlpha]

Well today I cleaned up my ConRods. 

They are tarnished in places so I clamped my drill in a vice and fitted a wire brush. 

 

 

 

 

 

 

I made sure not to clean inside the wrist pin area, apart from the chamfered area, and I left the old big end bearing shells in to protect the big ends but there is some tarnishing on the underside of the bearing face (the machined area). I will have a go at cleaning this with metal polish?

 

 

Here they are after a bit of work:

 

 

 

 

 

The marks on the faces above is just WD40 an a bit of residue oil.

 

Before I use them they will be checked for ovalness and re-balance before having the Pistons fitted. 

Hmm, now do I use them for the Deck Height check or should I wait until they have been check first, in case they are knackered??

Would seem sensible to get them checked first - damm, should have left them with the machine shop!!

[JonnyAlpha]

 

Someone posted this great pic a few days ago. Actually doesn't look as if it has any negative effect if filled there with RTV as the gearbox flange is there any way.

 

What a stroke of luck. 

Looks like an oilway that goes to the thread on the Oil Pressure Switch?

In the edited pic below I have marked what I think are the correct locations with the two red crosses.

The top one had silastic in it and the bottom one on the side of the block looks to have been brazed closed. You can just make it out in the pic I posted above of the bored block, a brazed circle below the Oil Pressure Switch hole.

 

Should I be concerned / do anything about this?

 

 

 

I have just been watching part of the Bill Sollis Ultimate Mini Engine Builder and noticed on his Metro block, he too has the same hole brazed up. I have taken and marked a screenshot:

 

 

I do need to double check that it has indeed been blocked off - need to make a note somewhere.

[JonnyAlpha]

Oh and jumping ahead to the final preparations, after Bill has had the engine painted he ran a needle file around the tops of the bores to remove the edge? Just wondering if I should do the same. I also believe the stud holes on the block face need to be chamfered, if so what's the best method for doing this?

 

[JonnyAlpha]

So, no responses to the above post - to be honest it's seems a little quiet on the Forum of late?

 

Anyway, latest bits arrived today. After much thinking I bit the bullet and forked out £100 for a set of ARP Con Rod bolts from Med Engineering.

 

 

They didn't come with any Torque Settings though so I will have to find that out?

 

Whilst some have said re-use the old bolts, even though I know I took them off and they were OK, for peace of mind I took the sound advice of fitting them to ensure they were bullet proof.

 

I was battling between ARP Con Rod bolts and ARP Head Studs but I figured the most important of the two would be the Con Rods as a failure there would be catastrophic, whereas the chances of a Head Bolt coming off would be less and, to my knowledge cause no damage (apart from I guess a warped head )?

 

I will be replacing the head studs but probably not for ARP more likely a Mini Spares competition head stud kit like this.

 

A few other tools arrived, some went to the parcel depot so I'll have to get them Friday. 

 

1. Soft Magnetic Jaws for my vice

2. A set of Moore and Wright Micrometers

3. A set of telescopic gauges

 

I will also be picking up a Laser Piston Ring Compressor from Halfords and a set of 32 blade mm / AF feeler gauges. 

[Cooperman]

The very light chamfer at the top of the bores is to help prevent the rings from fracturing when the piston/rod assembly is fitted. Use either a hand scraper or a fine draw file and some emery cloth.

A very slight chamfer at the top of each stud hole is also recommended and this can be done using a 1/2"  diameter drill running at slow speed. It needs to be a maximum of around 1.5 mm x 45 degrees.

[DeadSquare]

Just to clarify, the 1.5mm chamfer only refers to the stud holes.

 

Using a good quality ring clamp and care to only clamp the ring portion of the piston, I have never had any problem inserting the rings into a bore.

 

With an 848 cc engine, chamfering the bores is fine, but with a bored out 1275, if there is anything more than the minimum chamfer on the adjacent cylinders, there won't be much for the head gasket to sit on.

 

.

[DeadSquare]

To any one reading this..........I don't know where the photos have gone, but J Alpha will understand.

 

 

 

 

Top photo:- Run a little triangular file round the bolt threads and either blow out the holes with an airline or wrap string round a bit of wood, grease it and firk it in the hole in the block.  If the thread is badly damaged, the hole in the block should be helicoiled.  These bolts do not take much strain, they don't do much more than hold the aluminium to the block to keep the oil in. The strain is taken by two dowels.

 

Next photo:-That white stuff must come out, and out of the one at the front, and a stepped dowel holds the gearbox in the correct place under the block.

 

   "      "     :- That is the pressure relief valve, there is either a ball or a thing like a thimble on the other end of the spring.

 

   "      "     :- They take a two piece bracket, between which one end of the engine stabiliser fits.  these need cleaning out;  they are 5/16 UNF.

 

A big screwdriver, either side, behind the sprocket, with successively larger rods (drill shanks) as fulcrums, and keep heaving on both at the same time as equally as you can.

Edited by DeadSquare, 20 September 2019 - 11:41 AM.

[JonnyAlpha]

To any one reading this..........I don't know where the photos have gone, but J Alpha will understand.

 

 

 

 

Top photo:- Run a little triangular file round the bolt threads and either blow out the holes with an airline or wrap string round a bit of wood, grease it and firk it in the hole in the block.  If the thread is badly damaged, the hole in the block should be helicoiled.  These bolts do not take much strain, they don't do much more than hold the aluminium to the block to keep the oil in. The strain is taken by two dowels.

 

Next photo:-That white stuff must come out, and out of the one at the front, and a stepped dowel holds the gearbox in the correct place under the block.

 

   "      "     :- That is the pressure relief valve, there is either a ball or a thing like a thimble on the other end of the spring.

 

   "      "     :- They take a two piece bracket, between which one end of the engine stabiliser fits.  these need cleaning out;  they are 5/16 UNF.

 

A big screwdriver, either side, behind the sprocket, with successively larger rods (drill shanks) as fulcrums, and keep heaving on both at the same time as equally as you can.

 

The photos Deadsquare is referring to can be found on this post here. This is an old question that has been resurrected after posting this thread ref tools.

[JonnyAlpha]

OK so I started the trial build. Couple of questions / observation cropped up:

 

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

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.

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

4. Do I need to lube the thrust washers?

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

 

Heres today's progress:

 

Quick 5 minute rub with a wet stone on the face of the block, ready for doing the deck height:

 

 

Blew everything through with and air line and wipe the bearing housings with thinners. Wiped the bores with some WD40.

 

I noticed that one of the oil holes in the centre bearing housing has what looks like a brass insert?

 

 

I cleaned the 10 thou oversize bearing shells with thinners and when fitting them I noticed that the oil hole in the one at the Flywheel end is not centred on the hole in the housing - what do I need to do here?

 

 

 

I then carefully inserted the bearing shells and applied some Torco build lube:

 

 

 

I then pulled the Crank out of its polly bag cocoon and to my horror found that it had developed surface rust on all the non machined surfaces!!! So I then had to spend about an hour scrubbing carefully with some scotchbrite and WD40. After a wipe down I cleaned the bearing faces and journals with some thinners.

 

All nice and clean:

 

 

I'd also hadn't cleaned up the bearing caps, so then spent some time doing them:

 

 

In between watching the Bill Sollis Ultimate Mini Engine, I fitted the bearings into the bearing caps, lubed them up and fitted them. I torqued them up to 67NM and the crank still span nicely.

 

Next I turned the block on its side, set up the DTO gauge and checked the Crank End Float:

 

 

 

 

Next job - loose fit the pistons and check the Deck Height.

[GraemeC]

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).

[cal844]

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.