FH - followers, pistons and barrels

 With the little QR50 out of the way and the FH back on the bench, we can get on with the build. The barrel has been painted for a while, the bottom end is in the bike, there's no primary or timing side and no pistons. Off we go:

First step is to fit a circlip to each piston; the gudgeon pins come out with some mild warming and are refitted just as easily. As you can see, I've put a large rag under the pistons as I don't want a circlip in the crankcase at this stage, and the pins go back in and the circlips go on without any drama.

Next, we can refit the reground cam followers. I've ground the radius back into these such that they now have no wear grooves. The retaining screws and pins (with the missing ball) have been refitted:

Next, we fit the ring compressors - these are just strips of tin held in place with ty-wraps. These were cut for the SQ4 and are not really long enough for these larger pistons. You'll see the wood - these are to prevent the pistons rocking about when the barrel goes on.

Before the wood strips go in, we squirt oil all over both small ends. 

The wood strips are wide enough to completely stabilise the pistons while we put the barrel on, but first we use Threebond 1215 to apply the base gasket to the barrel, to keep it out the way. This wasn't ideal as I was forever wiping gasket goo off my gloves -  it would have been better to have the gasket, goo down, on the crankcase and apply the goo to the upper side after the barrel was over the rings.

After a lot of fiddling, swearing and anguish the barrel went down. The compression rings were not too bad but the three piece oil control rings, with their thin 'rails' were a pain to get in as they popped out of the compressors before they were caught by the barrel.

They went in eventually, and we can retain the barrels with four nuts.

FH - Plastiguage and the big ends

 Next step is to check the big end clearances. I've measured the journals, but I wanted to get some evidence of the clearance that I had ended up with after fitting new -0.030" shells. There isn't much detail on what the acceptable clearance is  before you must regrind, other than the data describing the sizes you regrind to and the recommendation that there should be minimal clearance after regrinding.

Waller indicates 0.003"- 0.004" for the big end shells used on 1948-1955 Square Fours (Fifth edition page 37); Phil Irving quotes 0.001-0.0015" clearance per inch of diameter (Tuning for Speed 3rd Edition), which equates to 0.00165 - 0.0025" for my 1.65" big end. Mr. Irving, otherwise known as 'Slide Rule' using those delightful pseudonyms beloved of motoring writers in the '40's, also notes that the clearance can be much larger as long as oil pressure is maintained.

So, let's introduce Plastiguage. This is a paste, extruded into rods a bit like Plasticene. You trap a bit in the bearing and squash it, so that the known Plastiguage rod diameter is squashed to take up the clearance of the bearing - you then use the card provided to determine the clearance from the width of the squashed Plastiguage. Plastiguage comes in different sizes to measure different clearance ranges.

So, you cut a length to suite the bearing like this, and then you make up the bearing. You make sure the bearing is clean first.

When you open the bearing again you can see the squashed Plastiguage and you can compare it to the card. This suggests something like 0.002 - 0.0025" clearance for the drive side. I'm happy with that.

This is the timing side, and it's about the same:

All good there then. Next job is to make sure the oil flows into the big ends. I'll inject it into the timing side oilway:

And it comes out the drive side big end!

During this process, I removed (with a little heat) one of the gudgeon pins from the new IMD 7.25:1 pistons I got from the AOMCC so I could check the fit in the connecting rod little end bearings. This proved to be perfect once I had cleared a small burr from one side of both bearings; not sure how that came to be there.

Happy days.

QR50 - engine top end

One of the things that was apparent from the beginning that the piston needed replacement, as there was a large crack in the skirt. I measured up the bore and determined that the bike was still on the standard bore, and bought a new piston assembly from ebay - new rings, circlips, piston and pin:

Fitting wire circlips is always a bit traumatic. I did lose this one, found it again, and fitted it successfully the second time:

I resprayed the barrel with B&Q barbeque paint, as I used on the exhaust. We'll see how that turns out!

The original head had a lot of fins missing. This one came from eBay:

Gudgeon Pin Extractor

Gudgeon or wrist pins retain the piston to the connecting rod with varying degrees of clearance, transition or interference fit according to the predicted running temperature of the engine, and are retained by a circlip at each end in addition to any fit. This means that removal of the circlips will sometimes allow the pin to slide out, but more often than not you'll need to warm the piston such that it will release its grip on the pin. Obviously, belting the end of a tight pin will do your connecting rods no favours at all, so anything other than light tapping is a no-no.

A much better approach is to use a gudgeon pin extractor. These usually consist of a threaded rod passing through the pin, some means of holding the pin, a tube large enough to allow the pin to come out and a large washer to spread the load.

I made this extractor to deal with the FH gudgeon pins, which were quite tight. It is made of a bit of 1" tube, with a closed end turned from aluminium; that's M6 threaded rod in the middle. The tube is long enough to accommodate a 3" gudgeon pin.

A turned steel plug fits neatly into the gudgeon pin aperture in the piston and is reduced to just fit inside the pin such that it doesn't slop about. It's threaded M6 internally and is retained with a nut for the moment.

Here it is, set up and ready to extract the first pin:

Here's the extractor set up on the piston. The end of the tube is shaped to fit the piston, spreading the load over the piston wall:

A blast of heat on the piston crown and some steady winding are all that is necessary to draw the pin out of the piston, without placing any side load on the connecting rod. When you have done winding, the pin is neatly enclosed in the extractor:

Job done.

Todays progress...

One pic today - and you'd have to have eagle eyes to spot what I have done!

Circlips fitted, small ends lubed up with engine oil, cams lubed ready for the block to go on.

I've also stripped the primary case off (& helicoiled a couple of holes), ordered the chains from Draganfly, cleaned out the battery carrier threads (which were full of paint), and tidied up the shed a bit.

Next stop, ring compressors. As it happens, 8-9 hours after writing the foregoing words this morning, I did do a bit more today. I finished my tin-strip ring compressors and did a trial fit of the barrel (well, it would have been THE fit of the barrel, had I not found that for some reason Number 1 piston will not slide gracefully into its cylinder, likes its brothers have done). The compressors work brilliantly though:

 

Base gasket in place ready for tomorrow:

A monumental day

Pistons in, rings properly fitted!

Starting on the engine!

Well, summer's here and the bike is coming together. I've finished my welding work, the wheels are still away, and most importantly I have some time away from work to get to grips with things at home.

So, in a break from repainting the kitchen we will start work on the bottom end.

 

I'm dithering around polishing the crankcases which is a noisy & messy job & which stops me rebuilding the engine. Someone also suggested that polish would hinder cooling - but equally it is obvious that the engine was once polished - it is deeply tarnished now, but you can see it is still very smooth - you can also where it wasn't polished!
 

But, I have all the parts and can get moving with the rods & cranks.

 

You'll recall from previous posts that the rods have been cleaned and polished and have spent the winter protected by some pipe insulation in their own box. I have small end bushes and big end shells from Drags along with new big end nuts, also from Drags.

 

These are shown in the adjacent picture and will have to be pressed into place and reamed to the finished size.

 

The sizes are shown in the table below and are around 11/16" - but will have to be sized to fit the factory specification using a suitable adjustable reamer. In this case we will use a 21/32" - 23/32" reamer, which are readily available but are of highly variable quality. Beg, steal or borrow a decent one if you can! If you must buy an internet cheapie, take a look at a few things before you use it and if it is no good, send it back!

Take the reamer to pieces. Measure the length of each blade, and make sure they are equal.

1. Look at the retaining nuts, make sure they are not too loose and clean the threads
2. Clean out the grooves in the reamer body and make sure the blades can sit snuggly down in the grooves. You don't want any swarf in there.
3. Put the reamer back together, and measure the diameter across two opposite cutting edges (this only works on six blade reamers) at each end of the blade. The dimensions should be the same! They are not supposed to be tapered. Repeat the operation for the two other pairs of blades.

So, to fit the bushes. You can use a press for this, if you have access to one, but a bench vice comes a close second. You could also use the draw-bolt method, but I suggest the loads are probably too high for that approach. These bushes are quite tight.

1. Find a socket or a piece of tube which is small enough to support the small end eye, but large enough, both in length and internal diameter, to receive the old bush.
2. Open the vice enough to receive the rod, the socket and the new bush plus a couple of millimeters.
3. Find a piece of soft sheet (brass for example) to protect the end of the new bush.
4. Align the socket, the rod eye and the bush. You might benefit by putting a short rod of about 1/2" OD inside the assembly, just until you have the new bush a couple of millimeters into the rod, just to keep things lined up.
5. Nip the whole lot up in the vice with your protective sheet on the jaw pressing on the new bush.
6. Operate the vice to push in the new bush, pushing the old one out into the socket. You will probably find the initial force required is much higher - and you might get a bit of a bang as the bush starts to move. This is normal. Don't be afraid to apply a bit of heat to the small end eye to get it moving - but go easy, this is aluminium. No Oxy-acetylene here!
7. Carry on pushing until the new bush is more or less flush with the face of the rod. My bushes are about 0.5 mm over length at the moment.

The next job is to drill the oil hole. Do this before reaming and you don't need to worry about deburring later. The Square Four has 3/16" holes in the small end eye.

Next - reaming to size. Get ready with your gudgeon pin, your internal micrometer or bore gauge & a 1" micrometer.
 

Now, adjustable reamers are really scraping devices. They are designed to scrape out small quantities of metal from holes and as you have seen (from when you inspected your new reamer) they are not as rigid as solid reamers and can only be used to take small cuts.

When you set the reamer up for the first cut, back off the adjustment collars (i.e. screw them away from the square end of the reamer) to reduce the diameter of the reamer until you can put the reamer into the bush. Now adjust it larger until it just begins to touch the inside of the bush. Turn it using a tap wrench a couple of times with some oil.

Be careful to twist the reamer such that it is concentric with the bush; make sure the blades pass right through the bush. That way you will minimise the potential to cut a tapered hole.

You want to increase the size of the hole in very small steps, testing with the gudgeon pin at each stage -  DON'T SKIMP ON THE CHECKING!! Small end bushes are relatively cheap, but replacing them repetitively is tiresome. Increase the size of the cut by turning the collars by 1/8 of a turn each time, and turning the reamer in the hole 3 or 4 times. Always make sure that the top collar is tightened down.

 

A few more thoughts:

• NEVER turn the reamer BACKWARDS – can You could break or chip a blade.
• Never put more than ¼ turn on the collars
• If the reamer jams, loosen the blades and pull the reamer out and start again. Remember a jam will leave a number of ridges and these have to be cut away or it will happen again.
• Make certain that the collars are tight.
• Clean the reamer after each pass.
• Do not push down on the reamer too hard or it will jam. Take it slow and easy - this is supposed to be a hobby remember? You don't need to hurry, you are enjoying yourself right?
• On each turn try to stop in a different place.
• Use oodles of cutting oil.

So, now we have our reconditioned connecting rod:

So, repeat the operation for the other rods and you will end up with a little heap of scrap like this:

So here is a table showing the dimensions I have ended up with:

	Small End Bush	Big End
Factory Specification	0.6868” 0.6863” 0.003" wear allowable	1.375” min (journal)
Cylinder 1	0.686”	1.3765”
Cylinder 2	0.6869”	1.3745”
Cylinder 3	0.6863”	1.377”
Cylinder 4	0.686”	1.3775”

I had to order a couple more bushes from Drag's since I wasn't happy with No. 2 & No. 3. The table above shows the new dimensions.

And now, over the last couple of days I have polished the cases. I made sure that I polished only the areas that were polished in the factory all those years ago:

Next stop, bottom end assembly!