steveg
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Jan 30, 2023 21:19:58 GMT |
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I'm trying to rebuild a 1.6 engine for my 106. Oversize pistons (standard) aren't available from anywhere I can find so when a set came up for sale on marketplace I bought a set.
I left them with the company who could rebore the block and asked if they could ensure they were going to work, at this point I couldn't check as they already had the old pistons. Not heard anything for a few weeks so rang them today and was told there is a problem.
They didn't check the pistons and rebored the block +1mm and on trying to fit the new pistons on the rods they found the pistons aren't wide enough to get the rods in. The pin fits OK though.
The worrying bit is that they don't seem to have any idea what to do to fix it. Has anyone else made the wrong pistons fit onto the wrong rods ? Making the rods narrower would seem the easiest solution the guy doing it says they are about 1-2mm too wide.
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Last Edit: Feb 26, 2023 13:11:45 GMT by steveg
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Jan 30, 2023 22:07:31 GMT |
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Theres plenty of TU stuff about, just not standard ! I don't know specific details of rhe tu myself, only mild dabblings, more of an XU man but been involved with some nice builds.
How wide are the rods? I presume they are a bushed type and crank located or are they piston located?
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steveg
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Jan 30, 2023 22:34:57 GMT |
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I don't know the width as the machine shop has them and the guy wasn't really saying much. Not sure I understand what you mean about the location, but the rods are bushed and the pistons need to be heated to get the pins out.
The pistons I bought are supposed to be copies of a Mahle one thats no longer available. I thought I had got lucky finding them as the alternative would have been very expensive specially made ones (the machine shop could source) or Woosner high compression ones nobody has in stock at the moment.
Having already done the head and crank and bought a load of stuff to put it together this is getting a bit expensive !
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stealthstylz
Club Retro Rides Member
Posts: 14,477
Club RR Member Number: 174
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106 Pistons and Rods.stealthstylz
@stealthstylz
Club Retro Rides Member 174
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Jan 30, 2023 23:34:12 GMT |
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If the rods are bushed you shouldn't have to heat anything to get the gudgeon pins out. The press fit is between the gudgeon pin and small end of the con rod, with the piston floating on the gudgeon pin. A piston designed for a press fit gudgeon pin usually won't work on a floating type bushed con rod as they don't usually have the circlip grooves machined in to retain the gudgeon pin inplace.
You ideally need to find out what rods are supposed to be used with the pistons. They could be for trapezoidal small ends which would make machining your rods to match more difficult.
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steveg
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No circlips just assumed the pistons had to be heated but the pin needs to be removed from the piston. Wasn't expecting there to be any problems but the only way to make things fit would be to machine the sides of the little end or make the gap between the sides of the piston larger.
Got a feeling the pistons I was sold are not the correct ones.
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stealthstylz
Club Retro Rides Member
Posts: 14,477
Club RR Member Number: 174
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106 Pistons and Rods.stealthstylz
@stealthstylz
Club Retro Rides Member 174
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If you get some photos and/or part numbers up of all the parts I could possibly advise. Modifying con rods or pistons isn't uncommon, but it needs to be very precise.
*I've got a vague recollection of what pistons you're talking about as I did a couple of oddball 1400cc TU engines but with bores over 1600 size and 1100cc cranks.
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steveg
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Jan 31, 2023 23:29:45 GMT |
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I could modify the parts myself but haven't had all of the parts in one place to look at them, I've got no way to re-fit the pins either.
I thought getting a proper engine place to do the work it would be easier!
Thanks for your help though.
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stealthstylz
Club Retro Rides Member
Posts: 14,477
Club RR Member Number: 174
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106 Pistons and Rods.stealthstylz
@stealthstylz
Club Retro Rides Member 174
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You just need a blowtorch to refit the pins. Make sure they move smoothly through the piston then heat the little end of the rod, drop it in the middle of the piston then push the gudgeon pin through. It's a one shot deal though, if you get it wrong it's not easy to adjust them without damaging the piston. You've got about a second between getting the pin through the lot and the rod contracting onto it.
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steveg
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Had another look at the parts catalogue and there are different rods. Trying to find out now for certain if the width of the small end is different.
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Last Edit: Feb 3, 2023 19:05:18 GMT by steveg
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Have you thought of removing material from the inside of the piston to give clearance for the rod width?
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steveg
Posted a lot
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Have you thought of removing material from the inside of the piston to give clearance for the rod width? I did but for some reason the engine place hasn't they seem very reluctant to offer any suggestions. |
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stealthstylz
Club Retro Rides Member
Posts: 14,477
Club RR Member Number: 174
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106 Pistons and Rods.stealthstylz
@stealthstylz
Club Retro Rides Member 174
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A lot of places won't do those sort of "unknown" modifications due to the hassle if it goes wrong. It'll all be based on a educated guess which tends to put them off.
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steveg
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Thanks for the replies.
I've found out a bit more over the weekend. The gudgeon pin is a tight fit in the rod and as standard there is a fair gap between it and the inside of the piston. I could probably get away with a burr or similar but if I am prepared to struggle I have a little mill I could use. What I don't know is how much material I can remove.
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steveg
Posted a lot
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Feb 10, 2023 12:45:34 GMT |
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Just been to pick my engine up and the pistons are just wrong. On the plus side it does look like I could gain the clearance needed by machining out the inside a bit. I will take a few pictures when I get round to it. Just wish the guy who sold them to me had been honest as I could have sorted something out before leaving it at the engine place.
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stealthstylz
Club Retro Rides Member
Posts: 14,477
Club RR Member Number: 174
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106 Pistons and Rods.stealthstylz
@stealthstylz
Club Retro Rides Member 174
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Feb 11, 2023 16:33:57 GMT |
This is what I have got. The old pistons have a 27.5mm gap for rod and the new ones have 21.7mm. The rods are 24mm wide across the small end. Any engine experts around who might be able to advise where it would be best to remove material from. Engine place suggested taking some from rod and some from piston. Ideally you're looking for around .050"/1.27mm minimum side clearance on each side of the rod, which means your target piston width would be 26.54mm which means you need to find 4.84mm total, rounded up for safety you need to take 1.25mm of each side of the piston and 1.25mm off each side of the rod. You also need to measure the gudgeon pin to inside of the piston CROWN to make sure the rod will clear that, and I'd recommend doing one then doing a dry build into the block to check there's side clearance present throughout the range of motion. |
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steveg
Posted a lot
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Feb 11, 2023 17:12:40 GMT |
This is what I have got. The old pistons have a 27.5mm gap for rod and the new ones have 21.7mm. The rods are 24mm wide across the small end. Any engine experts around who might be able to advise where it would be best to remove material from. Engine place suggested taking some from rod and some from piston. Ideally you're looking for around .050"/1.27mm minimum side clearance on each side of the rod, which means your target piston width would be 26.54mm which means you need to find 4.84mm total, rounded up for safety you need to take 1.25mm of each side of the piston and 1.25mm off each side of the rod. You also need to measure the gudgeon pin to inside of the piston CROWN to make sure the rod will clear that, and I'd recommend doing one then doing a dry build into the block to check there's side clearance present throughout the range of motion. Thanks, initially thought I might just get away with machining the pistons but there isn't a huge amount of material around the underside of the pin bosses plus it will make them a fair bit narrower. The rods have about 1.5mm to 2mm extra on the casting before you start machining away anything more than cylindrical bit if that makes sense. I hadn't got as far as considering the clearance under the CROWN. I think I will make a dummy gudgeon pin so I can fit the pistons and check the CROWN to deck height anyway so I can check both at the same time. Bit annoyed with the machine shop as they are perfectly capable of sorting it out. I can probably do it at work but it always causes hassle doing homers and it isn't something I want to rush really. Do you do this sort of thing for work or have you just built a lot of engines ? |
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stealthstylz
Club Retro Rides Member
Posts: 14,477
Club RR Member Number: 174
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106 Pistons and Rods.stealthstylz
@stealthstylz
Club Retro Rides Member 174
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Feb 11, 2023 18:33:16 GMT |
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I've done it before at work a handful of times, it's mainly been on V8 stuff though that is bigger overall. AFAIK the main reason the clearance is there is because of design and/or tolerances the crank pin isn't always central the the cylinder bore so you need the space to allow the piston and rod to be slightly offset
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steveg
Posted a lot
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Feb 11, 2023 21:02:18 GMT |
I've done it before at work a handful of times, it's mainly been on V8 stuff though that is bigger overall. AFAIK the main reason the clearance is there is because of design and/or tolerances the crank pin isn't always central the the cylinder bore so you need the space to allow the piston and rod to be slightly offset Appreciate the advice thanks. Apart from building a half decent Mini engine from a kit years ago I have only ever built up standard stuff. Although the blocks been dunked in a cleaning tank I will have to thoroughly clean it, paint it and fit the crank. Then I can have a better look at the pistons. |
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