I was wondering when you change from 33 to 35 mm intake valves does the valve seats OD remains the same and the machine shop opens the ID or they completely put new oversized seats and they rework head to accept bigger seats. I will also do the work in situ, remove head and replace camshaft. I know I know you will said that removing engine is easyer but then I will have to move the engine to our apartment living room and this will make the lady of the house a little upset. If you have any pics of your reworked and polished head please feel free to post.
Tuning Looking to go faster
- Thread starter gordinir8
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Tuning Looking to go faster
the hobbler
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The machine shop will remove the old valve seats, open up the fitment apertures a little bit and then fit the new, larger valve-seats. If you are (wisely) only going up to 35mm, there is plenty of room in the combustion chamber for the 35mm valve seat. Does you good lady not realise that you will be bringing in a 'work of art' into the living-room? Tch, Tch. And just incase you are wondering---my 'er indoors would shoot me if I 'suggested' that the engine should be overhauled in the living-room!
Tom tell her she is overreacting, here is my engine when i bought it, unfortunately now in this position we have our Christmas tree.
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the hobbler
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Very simply Thomas, I am not that brave (or stupid), but how can she NOT regard that as a work of art? Have a good christmas, all the best for 2022
Here are some pics of the head after about 12000 kilometers, exhaust valves and spark plugs are white while there is a small crack between valves, i don't now if this is going to be a problem or bigger inlet valves will make it worse. Also head seems that it hasn't skimmed before so i was wondering if it will be a good idea to take it down a little like 05mm. Before removing the head i measured the inlet valve lift and found it 8.5mm The new cam that i want to buy says max lift 7.2! is this possible, the new cam to has less lift?
the hobbler
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Cracks between the valve seats seem to be quite common on '126' heads, but it doesn't seem to affect there running. However, it might be worthwhile having a word with the people fitting your new valve seats what their opinion is. It might be that whilst they have the old valve seats out they can repair the crack. If your cylinder head has NEVER been skimmed, it is quite safe to take 40 thou (1 mm) off. This will still leave some of the 'exhaust-blow' ring in place.
Tom i was thinking of 0.5mm and 0.6mm cooper gasket. Now i can follow your advice and take it down to 1mm but in that case what gasket size? Does it need to be cooper or not? (i hope push rod tubes will still fit) there is no need to spend money if it is not necessary . What is your opinion about the white color valves?, i had a pre-ignition problem specially during summer and i think that this might me the reason. I am exited with this mod and i hope that along with the cam it will have some difference on the road without a new carb which will follow later and make it even faster.
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If, as I mentioned before, the head has never been skimmed on a previous ocasion, you will be able to use a 0.5mm copper head gasket as well as the 1mm head skim. There are 2 types of the copper head gasket available, depending where you buy it from---1 WITH a elongated hole to allow exhaust gasses to pass through the gasket and escape through the hollow shroud bolt (should the head-gasket blow)and 1 without the hole---try and obtain the gasket WITH the hole. If you can't, make the hole yourself.
The whiteness of your exhaust valve stem, and the pre-ignition you suffered most probably IS a sign of too weak a mixture. Even if you take 1mm off the head and use a 0.5mm copper head gasket, your push-rod tubes should be able to cope. I personally use the 'spring-loaded' tubes because (a) they look nice and, (b) in the long run, they work out no more expensive than the normal 'concertina' versions because you only ever have to renew the seals, no matter how many times the head is removed/re-fitted.
So removed pistons, unfortunately they have seizure markings, specially the one closer to the firewall (i call this No2 cylinder) while cylinders inside are clear. Before i make a detailed measurement i think those need to be discarded anyway, what you think?. What concerns me more is why this happened and how i am going to avoid it in the future since this engine has only 12000 kilometers .
Tomorrow will measure cylinder bores and decide about which oversize piston i will buy.
Bellow are fits and clearances as Tom 'the hobbler' told me so i put them here just for ref.
Hi Thomas---652cc
"B" pistons are:---76.390mm to 76.940mm---bore diameter:---77.010mm to 77.020mm
"C" pistons are:---76.940mm to 76.950mm---bore diameter:---77.020mm to 77.030mm
Piston clearance in bore is from 0.070mm to 0.090mm
Piston over sizes are (should!) available +0.2mm---+0.4mm---+0.6mm.
Tom
Tomorrow will measure cylinder bores and decide about which oversize piston i will buy.
Bellow are fits and clearances as Tom 'the hobbler' told me so i put them here just for ref.
Hi Thomas---652cc
"B" pistons are:---76.390mm to 76.940mm---bore diameter:---77.010mm to 77.020mm
"C" pistons are:---76.940mm to 76.950mm---bore diameter:---77.020mm to 77.030mm
Piston clearance in bore is from 0.070mm to 0.090mm
Piston over sizes are (should!) available +0.2mm---+0.4mm---+0.6mm.
Tom
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the hobbler
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3 Things will cause those marks on the pistons---engine getting too hot----pistons have TOO much clearance---pistons have not ENOUGH clerance,and therefore a possible cause of it running hot. I agree, the pistons have to be changed; if the barrels are OK, go up to +0.4mm---this will take you to 659cc---but give the new pistons to the machine shop so that they can make the barrels match.
I have never seen that much of a clearance before, managed and put 0.30mm filler gauge between piston and cylinder wall and I am sure if I measure it properly it will be even more. I will agree with you Tom this might be the the reason. This also explain piston rattling on hot days and under load as well as 500-600 ml of oil consumption per 1000 kilometres
Just measured cylinders, both are out of specs and here is the worst one measuring at top, mid, and bottom cylinder found 76.92, 76.96, 76.94 while piston found 76.24, 76.44, 76.53 accordingly. This is a gap of 0.68, 0.52, 0,41 all in mm.
the hobbler
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It would seem Thomas that you have just found the cause of (a) the marks on your pistons and, (b) the cause of your rattle--piston-slap!
the hobbler
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Also Thomas, and my mistake entirely (must re-train my fingers, or brain) "B" piston should read:--76.930mm to 76.940mm--apologies.
No worries Tom still out of specs but now makes more sense to me. I wonder how little car wasn't complaining more with those pistons on. Seems that the guy that overhauled the engine (for his use) hone the cylinders, put new rings and just kept the old pistons on.
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I think that you entirely correct in your thoughts---would seem that the previous owner did a "just enough to get it backon the road" job. Just shows how tough, and well designed, these little motors are.
I was thinking instead of buying new pistons and pay extra money for honing to buy this kit, it will cost me the same, I am just not sure about the quality. The cylinders I have now are made in Poland. Anyone familiar with this product?
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A lot of the Polish gear is quite well made---definately better than the 'Chinese' gear. If the barrels and pistons are a matched set, and at a sensible price, it would seem to be sensible to go for it! Just be careful that you put the pistons in facing the correct way and use plenty of lube. I would also reccomend that you run the pistons/barrels in properly. I normally run in a engine for 800 miles (1300 km) using a proper 'running-in' lubricant (one with a high zinc content such as Morris's 'pistoneeze'), and do a complete oil change at 400 miles (650 km). I limit the 'running'revs to about 3,500 (4,000on 'off-load down-changes')
