Please read the following text as it concerns the future of Bob's Boring

My name's Bob, and I've been reboring engine cylinders this time around for the last three, nearly four years. However, due to various circumstances I'm now having to give up reboring/honing, and will cease trading as of June 30th, 2022.

After that date I won't take on any new work, and I'll be taking down this website at the end of July.

Sorry to have to say goodbye, I had hoped to continue on for at least another five years, but since October 2021 things have changed very much for the worse, and I've decided that it's best for me to stop now. So I apologise to those of you who have seen this website and thought about having a cylinder rebored this coming Autumn or Winter, but now you'll have to find someone else to do the work.

All the best,  Bob

example cylinders, the one on the left has been rebored, and the one on the right has been rebored and honed

You can clearly see the difference between a rebored finish and a honed finish because the honing stones cut a neat cross-hatch into the rebored surface. 
     This does two things.
    1. It cuts through the work-hardened surface of the newly bored cylinder (the boring cutter hardens the surface as it bores the barrel)
    2. It helps the piston rings to bed in more easily, and helps to hold oil in the minute grooves of the cross-hatch.

These two cylinders came from a Rotax 462 cc water-cooled twin cylinder 2 stroke engine that powers one of my microlight aircraft.
(See the photos below to see my aircraft)

My microlights  (tip, to see a larger version of a photo, just click on it)

Minimax (Rotax 447)

This is my Minimax, a wood and fabric single seat tail-dragger type aircraft that's powered by a Rotax 447 air-cooled twin cylinder 2 stroke engine. 

The photo was taken just after I'd landed at my home airfield at London Colney. I'd just flown back from the Isle of Wight, where I'd been for a fly-in in 2018.

Raven Q hybrid (rotax 462)

This is a hybrid aircraft using a Medway Raven wing and a Pegasus Q trike. This aircraft is powered by a Rotax 462 water-cooled twin cylinder 2 stroke engine. 

The photo was taken just as I landed at Eshott airfield in Northumberland during the Fly-UK Round Britain Tour in 2016

Spectrum (rotax 462)

This is my Spectrum. It is the only flying example left in the UK, and is one of only 22 ever made. It's powered by a Rotax 462 water-cooled twin cylinder 2 stroke engine. 

The photo was taken just after I landed at Boxted airfield in Essex for their annual fly-in in 2018.

About Bob's boring + honing services

Hi, as I said above, I'm Bob, and I live in Borehamwood, Herts. From the photos above you can see what my hobby is. Others like to race, or to walk, or to cycle, or go canoeing, I like to fly, and to do this I own a collection of microlight aircraft. I do all my own maintenance on these aircraft, and as you can see from the photos at the top of the page, I rebore and hone the engines when necessary. To do this I now have a total of five portable boring bars and matching sets of honing equipment. (See the 'Workshop Services' page for further details) 

Years ago I worked for a motor re-engineering company in Bristol called Hartcliffe Engineering. Sadly they no longer exist, but I worked there from when I left school at the age of 15, until I was 21. During that time my main occupation was reboring and honing car, commercial, motorcycle and small industrial engines. 

Most of this work was done in the workshop, where I used a collection of Van Norman portable boring bars. The one I normally used was the 944, and I had two of them, but I also had a 905 and a 777S for larger bores. For some engines, such as Gardner diesel bus engines, the bore size at either 4.75" or 5" diameter, and with a bore length of over 8", was so large that the Van Norman's weren't big enough to rebore them. For these I used a pair of huge static Paddon-Thomsen boring bars, and centred the block under the cutting head instead of centring the boring bar over the cylinder as I did with the Van Norman bars.

the different types of Boring bar I used to use

Van norman 944/905

The picture above shows a Van Norman 944 portable boring bar. The 905 is just very slightly larger than the 944, but the design is identical.

van norman 777s

The picture above shows a Van Norman 777S portable boring bar. This bar is somewhat larger than the 944 and the 905, and correspondingly heavier. (Note the lifting hook on top of the gearbox!)


The picture above shows a Paddon-Thomsen static boring bar with a large diesel engine block mounted under the cutting head.

Honing in the workshop

When working in the workshop I used a Delapena Beam Stroking Honing Machine to finish the cylinder blocks I'd rebored. The picture on the right shows what they look like, and the one in the picture even has a Delapena honing head at the bottom of the honing shaft that hangs from the end of the beam stroking bar.

This was a very good tool, and was not only easy to use, but very safe as well, due to having a trigger next to one of the handles on the beam head. So if the honing stones jammed in the cylinder for any reason I could let go of the trigger very quickly to prevent injury to myself, and damage to both the cylinder I was working on, and the honing tool.  

I wish I had one of those today for honing out cylinders in my workshop, but instead I use the hand tools you can see on the 'Workshop Services' page.


As well as reboring/honing in the workshop, our company also used to send me to main dealerships sometimes to rebore and/or hone engines 'on site' at their premises. They also offered an 'in situ' reboring service, where I'd be sent out to a customer's site (both trade and private) to rebore an engine in the chassis. Although the engines I bored 'in situ' were mainly 1950's and 1960's, 4 and 6 cylinder inline car engines, I also had to rebore commercial diesel engines occasionally. For this I would normally use the Van Norman 777S, which is large and heavy, but as a young and relatively fit teenager I was able to lift it around without anyone else's help.

Having rebored the cylinders I then had to stand on the top of the engine block in order to hone them to the finished size, so it was necessary for there to be enough room above the engine for me to stand on it. It was also necessary for there to be a nearby electrical outlet that I could reach with the extension lead. So reboring cars in garages at the end of the garden wasn't normally an option unless the garage was well lit and had power, and a high enough roof for me to be able to stand upright on top of the engine block.

Although some years have passed since I worked for Hartcliffe Engineering, the training I received, and the years of practice I put in while working there have stayed with me ever since. I now have my own portable boring bars and honing equipment, and can offer you a reboring and honing service either at my workshop in Borehamwood, or at your premises.

Furthermore, because I did quite a lot of 'in situ' reboring then, I have retained the skills necessary to offer this service to my customers now. So if you have a car/van that has good access to the top of the block, and doesn't have either Nikasil coated liners or the gearbox in the sump (BMC minis etc) then it may be possible for me to rebore it for you while still in the chassis. (See the 'In Situ' page for further details)


All prices are per cylinder, (I don't charge by time, but I will charge extra if the number of cuts exceeds two cuts per bore. Please see the Prices page for further details). Also, the price I charge includes boring to an agreed oversize with the customer and finishing the cylinder to a cross hatch finish with the honing tool. If the customer supplies the piston(s) I check and match the piston skirt clearance against the manufacturer's published specifications.


Customers are welcome to provide their own oversize pistons either prior to the rebore, or after it if the expected oversize is not enough to remove the wear ridge, and a larger oversize is required. However, if the customer prefers I can supply the piston(s) as well.

cylinder material

The type of material has an effect on whether I can rebore a cylinder or not. For instance, I can rebore cast iron and mild steel cylinders, but I cannot rebore any cylinder that has been plated with a hard material such as Chrome or Nikasil or any other similar coating. As an example, please see the pictures below to see an attempt at reboring a cylinder that had a hard plating bonded to it.

You will notice that the aluminium casting did not react well to being cut with the fly cutter on the boring bar. Instead of leaving a smooth finish that can be honed, the coating has been ripped away by the tungsten carbide tip of the cutter, and the exposed aluminium casting behind the coating has been left with deep scores in the cylinder surface.

The damage is not recoverable and the cylinder in the photos had to be scrapped. So please check that the cylinder you'd like me to rebore does not have any kind of hard coating or plating before asking me to do any work on it.


Please either send me a message (in the message box below)

Or email me at: bobsboringuk@gmail.com

Or you can phone me on: 07956 689806

Let me know what service you require, and I'll do my best to help you with your requirements.


More than once recently, people have turned up at my door and have been disappointed that I wasn't in my workshop. So please be aware that I don't always work in my workshop, I often work out at a customer's site.

If you want to visit me then please phone me on, 07956 689806,  BEFORE you set off, in order to make sure I'm working in the workshop, or you may have a wasted journey!


By the way, if you have a classic bike, whether British or Japanese, why not check out Sump magazine at the following website?


They've got a link to this website so I thought I'd return the favour, and put up a link to their website as well. They certainly seem to know what they're on about in their articles, and I've enjoyed catching up on the classic bike scene.

Brings back fond memories of my old BSA's. I had a Bantam 175, and two B33's, one after the other. Those were the days!

Send me an enquiry in the message box below