Page 1 of 2 12 LastLast
Results 1 to 10 of 16
  1. #1
    Co-Pilot BobH's Avatar
    Join Date
    Jan 2010
    Location
    Borehamwood, Herts
    Posts
    379
    Thanks
    1
    Thanked 18 Times in 15 Posts

    Reboring and honing service

    Hello,

    I'm not sure where I should post this, but I'd like to advertise that I've recently acquired a Buma engine cylinder boring bar, and a matching set of honing equipment. This may not seem very ground breaking, as I'm sure others have bought such items for personal use in the past. The difference is that I was trained for 5 years to be an engine reborer and honer when I first left school, so I have some modicum of knowledge on how to use these things. As such I'd like to now offer my services as a professional engine reborer and honer for single, twin, and other multi cylinder engines where each cylinder is a separate item, or a twin cylinder unit, i.e. Triumph, BSA and Norton twins, etc.

    The reason I purchased the boring bar is that I'm going to be retiring from my present occupation soon (SQL and database reporting analyst programmer) and I'd like to take up something that will earn me some money and keep me off the streets when I retire.

    Technical details:

    The Buma boring bar has a boring range from 2.2" up to 4 3/8", so will rebore most if not all of the current Rotax engines, and quite a few others as well, provided they don't have Nikasil liners that is. It will also bore most vintage motorbikes and scooters (Triumph, BSA, Norton, Vespa, Lambretta, etc) so I'd like to advertise my services to those enthusiasts as well.

    However, I don't know if this is the appropriate place to put an advert for such services in the microlight world, or if there is a section that I haven't yet noticed on the forum, where such adverts should go.

    Any advice Vince can give me on this will be gratefully received, and I will be happy to move the ad to somewhere more appropriate if there is somewhere more appropriate to put it.

    Best regards,

    Bob Hood

    P.S. I've added some photos of the boring bar, tools, jig, and honing equipment, and some photos of the test bores I've done. Oh, and my location and contact details if anyone is interested are as follows;

    Location: Borehamwood, Herts (nearest airfields London Colney and Plaistows)
    Tel no. : zero, seven, nine, five, six, six, eight, nine, eight, zero, six
    Email : bob [dot] hood [dot] uk [@] gmail [dot] com


    Buma 1.jpgBuma 5.jpgTools 1.jpgJig 1.jpgHone 1.jpgBore top 2.jpgBore bottom 1.jpgBore top 1.jpgBore bottom 2.jpg
    Last edited by BobH; 17-01-18 at 16:51 PM. Reason: Adding photos and contact details


  2. #2
    Co-Pilot goldrush's Avatar
    Join Date
    Feb 2009
    Location
    Peterhead
    Posts
    956
    Thanks
    1
    Thanked 58 Times in 55 Posts
    Bob.. fron old decrepit old fa*t to another.....so glad you are looking forwards to a "boring"! retrirement

    Gotta be money in it... good opn ya!
    Wally Hayward


  3. #3
    Co-Pilot BobH's Avatar
    Join Date
    Jan 2010
    Location
    Borehamwood, Herts
    Posts
    379
    Thanks
    1
    Thanked 18 Times in 15 Posts
    Goldrush,

    I think you must be the first person ever to make that "boring" joke, well for the last 47 years that is!


  4. #4
    Co-Pilot goldrush's Avatar
    Join Date
    Feb 2009
    Location
    Peterhead
    Posts
    956
    Thanks
    1
    Thanked 58 Times in 55 Posts
    I seem to remember having also made it in my youth..................... some 65/70 years ago
    Good luck with your venture.
    Wally Hayward


  5. #5
    Co-Pilot BobH's Avatar
    Join Date
    Jan 2010
    Location
    Borehamwood, Herts
    Posts
    379
    Thanks
    1
    Thanked 18 Times in 15 Posts
    Hello,

    Just an update to let you all know that I've now acquired a second boring bar. This one is the SPS mini, which is much smaller and lighter than the Buma, and is designed for boring out motorcycle and scooter cylinders. As such it is better suited for boring out our Rotax 2 stroke engines.

    I have an advert on the Car and Classic website, and here's a link to it.

    https://www.carandclassic.co.uk/car/C1053818

    In the ad you can see that I've explained much more about the services I can offer, and also about my pricing structure.

    Best regards,

    Bob Hood

    P.S. I've added some photos of the two boring bars and jigs.

    Location: Borehamwood, Herts (nearest airfields London Colney, Plaistows, and Elstree)
    Tel no. : zero, seven, nine, five, six, six, eight, nine, eight, zero, six
    Email : bob [dot] hood [dot] uk [@] gmail [dot] com


    Bars 1.jpgStands 1.jpgBars and Stands 2.jpg
    Last edited by BobH; 21-02-19 at 18:12 PM.


  6. #6
    Co-Pilot Arielarts's Avatar
    Join Date
    Feb 2011
    Posts
    635
    Thanks
    40
    Thanked 88 Times in 80 Posts
    Excellent stuff Bob. Know where to come next time I seize the Lambo (again)...


  7. #7
    Co-Pilot BobH's Avatar
    Join Date
    Jan 2010
    Location
    Borehamwood, Herts
    Posts
    379
    Thanks
    1
    Thanked 18 Times in 15 Posts
    Arielarts,

    Is it still on standard size or has it been bored before? Oh, and what model is it? I went through two lambretta's when I was a mod, and three engines!


  8. #8
    Co-Pilot BobH's Avatar
    Join Date
    Jan 2010
    Location
    Borehamwood, Herts
    Posts
    379
    Thanks
    1
    Thanked 18 Times in 15 Posts
    Hello again,

    I've been playing with my new SPS toy and rebored my spare 462 barrels again. The pics below show one barrel rebored and the other one bored and honed. The one on the right, with the cross hatched finish is how I was always taught to finish a bore when I worked at Hartcliffe Engineering. However, in the blurb that came with the SPS bar, it says that as the SPS mini bar does a fine cut, the finish is good enough to use without honing afterwards.

    Personally I think you should always hone a bored cylinder, as the surface hardens to a certain extent when it's bored, and the honing stones cut through that hardened surface in order to produce the cross hatching. This wavy angled finish allows the tiny scratches to hold oil and therefore lubricate the rings while they're running in. It also helps to prevent the piston from seizing at the same time. So I don't think I'll be following the advice in the SPS blurb, but will continue to hone every cylinder I bore.

    Bored Honed.jpg


  9. #9
    Co-Pilot BobH's Avatar
    Join Date
    Jan 2010
    Location
    Borehamwood, Herts
    Posts
    379
    Thanks
    1
    Thanked 18 Times in 15 Posts
    Hello,

    I must say it never ceases to amaze me how ingenious people can be. A customer brought a 1978 Suzuki PE 250 barrel to me the other day, along with the piston. He's been having a lot of trouble starting the engine from cold and after doing all sorts, including replacing the carb with a brand new item, he decided that the compression was at fault. He wasn't far wrong either. The PE is a reed valve induction engine, so it relies on having a good vacuum in the crankcase when cold in order to suck the fuel air mixture in past the reeds. A worn bore and/or worn or broken rings, will reduce the compression above the piston, and the vacuum below it, so that less fuel can get past the reeds, particularly when cold.

    Here's a photo of the piston he brought with him.

    Piston holes1.jpg

    See the two little holes in the area where the piston has previously seized? Some bright spark decided to drill those after the engine had seized and been freed off, so that some of the petroil mixture would be forced through them and into the previously seized area every time the piston went down the bore.

    Clever? Yes! Good practice? No!

    Thank goodness the holes were as small as they were, or the piston could have cracked around them, and broken into pieces, which wouldn't have done it any good at all.

    The standard bore size on these engines was 67mm, with a stroke of 70mm, so it was undersquare. That's understandable, as the PE was designed as a mudplugger trail bike, with lots of low down torque and only 28hp. This particular one had been bored out to 67.6mm. Looking up the normal oversizes for this engine I couldn't find a 67.6mm oversize, the nearest was 67.5mm. However, this one had definitely been bored to 67.6mm, not 67.5mm. I measured it half a dozen times to confirm this, and the boring cutter marks are still in the cylinder wall at this size, so I know it's not worn the extra 0.1mm since being rebored. Furthermore, the cutter marks I just mentioned were in a sort of herring bone pattern, as though the cutter was blunt and chattering all the way down the bore. If I can I'll try to take some photos of it and put them here, as I've never seen cutter marks that bad before (and I saw a few back in the day!), you can even feel them with your finger nail.

    The piston shown above, was 67.3mm at the bottom of the skirt, which is where pistons are normally measured for clearance purposes. So the gap between piston skirt and the cylinder was over 0.3mm. 0.3mm is 0.012" but the actual clearance on this one was 0.013", and is more than three times the recommended gap for most engines, which is normally around 0.004", or 0.1mm.

    No wonder he couldn't get the thing to start! There must have been so much blow by at the rings and skirt when the engine was cold that there'd hardly be any vacuum for sucking fuel into the engine when cold. As the engine warms up the piston expands in the bore and takes up much of the clearance, so the compression increases at the top and the vacuum increases at the bottom, thus sucking in the correct amount of fuel mixture every revolution, and the weak mixture problem goes away.

    We've managed to find a 68mm piston in the US, so he's ordered it. It wasn't cheap, I think the total cost, including postage from the States works out at around 130 or so. When it arrives I'll see about boring and honing the barrel out to match it. I'll let you know how it all works out, and whether his bike starts and runs correctly after the piston clearances have been returned to factory spec.


  10. #10
    Co-Pilot BobH's Avatar
    Join Date
    Jan 2010
    Location
    Borehamwood, Herts
    Posts
    379
    Thanks
    1
    Thanked 18 Times in 15 Posts
    Hello again,

    Further to my last post about the piston with holes drilled in the side. I thought it best to update you all. The customer arrived yesterday with his brand new 68mm piston for his Suzuki PE 250 engine. It was made by Wiseco in America, and the customer had to buy it from there as there doesn't seem to be a UK agent for them. As a result we've had to wait for a week for it to arrive, and the customer was keen to bring it round to me last night.

    I read all the bumph that came with the piston in the box, and guess what? I was very surprised to discover that if the new piston arrives without the holes, then you have to drill them to match your particular engine! Who knew? It never occurred to me that Wiseco would put instructions in the box with it to drill two little holes into the side of the piston on the exhaust side, and in line with the central supporting bar that splits the exhaust port in two. I've never come across that before, and I've no idea if it's just on this particular make and model of bike that requires it, or whether there are other 2 stroke singles out there that need to have this done.

    I guess they've had issues with pistons seizing on this particular bit of cylinder wall because the supporting bar's got hot and expanded into the bore. That would also explain why the piston fitting instructions also say to 'relieve' the central support bar by .002" - .004". Interesting eh? Well, I've done what they required and drilled the two holes to the correct size, and in the location they specified. I've also 'relieved the face of the support bar by around .002" and made sure to chamfer the edges of all the ports in the barrel, to help prevent a ring from catching on an edge and breaking.

    One other thing though was that the skirt clearance is listed as .06mm (.0025") and at the correct bore size of 68mm there was not enough clearance. So I had to take out an extra .0005" in order to get the skirt clearance up to .0025". The problem is that with the skirt clearance now correct, the rings as supplied with the piston, have more than the specified .004" per inch gap, i.e. the gap should be just under .012", but with the extra .0005" to get the skirt clearance, the ring gaps are now just over .014". However, it does say on the Wiseco website that for aircooled engines one can allow up to .005" per inch gap. So all is not lost, and I can breathe again. Phew!!


Similar Threads

  1. Jabiru Service
    By Sean McDonald in forum Microlight Discussion
    Replies: 0
    Last Post: 24-07-16, 20:30 PM
  2. What service
    By john murphy in forum Off Topic Discussion
    Replies: 1
    Last Post: 19-07-14, 20:16 PM
  3. Gps update service
    By Blade 582 in forum Microlight Discussion
    Replies: 3
    Last Post: 12-07-14, 18:28 PM
  4. P&M Service Bulletins
    By FlyingBrian in forum Microlight Discussion
    Replies: 55
    Last Post: 16-06-11, 09:10 AM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •