dek
2nd Class Ticket
Posts: 29 
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Post by dek on Oct 6, 2019 14:37:39 GMT
T5 malossi 172, stripped it down and noticed at the bottom of the piston skirt there was a crack.
Could this have been caused by a previous seize as the piston has heavy scoring and there where marks on cylinder wall.
The crank also had heavy scoring on it.
Or could the crack be caused by piston to bore clearance, if so what should this be and is it just measured with feeler gauge around the top and bottom.
I have took some fine wet and dry to cylinder walls and it seems to have cleaned up pretty well.
The cylinder kit is 21 years old and grade 0, piston is a grade b.
I was looking at pistons and they only come in grades A B C and D, is grade 0 the same as A?
So my dilemma is what piston to get as I am concerned that maybe there is to much bore clearance and that's what caused crack in piston skirt.
It did sound extremely slappy, but I believe that's just how it is.
Cheers
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Post by citydaz on Oct 6, 2019 19:58:22 GMT
how about sending the cylinder to a reputable dealer for a rebore and ask them to match a cylinder to it?
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dek
2nd Class Ticket
Posts: 29
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Post by dek on Oct 6, 2019 20:13:38 GMT
I was under the impression that these cylinders cannot be rebored, cylinder seems to be fine nothing that catches a fingernail.
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Post by mijapxman on Oct 15, 2019 17:23:16 GMT
These cylinders can be rebored, but have to also be replated which makes it usually not cost effective.
These kits are known for sounding slappy as standard. Can't remember if they need a specific measuring technique, try measuring the same as you would a standard T5 barrel as mentioned in the Haynes manual?
Mij ☺
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dek
2nd Class Ticket
Posts: 29
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Post by dek on Oct 15, 2019 22:15:20 GMT
I used 3 set's of feeler gauges, put piston in the cylinder and using the 3 gauges measured around the top and bottom of the piston and it seems to be a pretty consistent 0.05mm gap.
In the Haynes manual bore clearance is 0.04mm. So not that far away.
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Post by mijapxman on Oct 19, 2019 11:03:18 GMT
I used 3 set's of feeler gauges, put piston in the cylinder and using the 3 gauges measured around the top and bottom of the piston and it seems to be a pretty consistent 0.05mm gap. In the Haynes manual bore clearance is 0.04mm. So not that far away. Remember to check the ring gap, when you fit new ones, Bud 😉. Also ,it may be worth asking a tuning shop, if it would recommend to go up a grade of piston size, no harm in asking 😉 Mij☺ |
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Post by harding05 on Oct 22, 2023 12:50:02 GMT
T5 malossi 172, stripped it down and noticed at the bottom of the piston skirt there was a crack. Could this have been caused by a previous seize as the piston has heavy scoring and there where marks on cylinder wall. The crank also had heavy scoring on it. Or could the crack be caused by piston to bore clearance, if so what should this be and is it just measured with feeler gauge around the top and bottom. I have took some fine wet and dry to cylinder walls and it seems to have cleaned up pretty well. The cylinder kit is 21 years old and grade 0, piston is a grade b. I was looking at pistons and they only come in grades A B C and D, is grade 0 the same as A? So my dilemma is what piston to get as I am concerned that maybe there is to much bore clearance and that's what caused crack in piston skirt. It did sound extremely slappy, but I believe that's just how it is. Cheers I've had the same problem two barrels old I've cleaned up with patio acid 1200 wet n dry and fine grinding paste bought new piston from malossi centre Italy right letter for barrel ect but sounded like piston hiting the head after head gaskets 1.5 or a malossi headgasket still rattle I research problem on line and saw it was similar to piston slap on cars but there were worn bores ect so I thought and noticed the piston ring was tight ie the barrel was easy to install not the normal poke the piston ring a sloted screwdriver ect so I have just removed barrel removed ring cleaned up ring slot with 1200 grit wer n dry a small smear of fine gring paste and without taking of piston cleaned up with petrol installed ring barrel ect started up no rattle completely gone so any piston from malossi might need clean of bur inside piston ring slot |
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Post by gpowell on Oct 23, 2023 20:38:16 GMT
Get the bore measured correctly with a bore gauge, then check piston sizes and clearances.
Nicosil lined barrels are not reborable like a traditional iron barrel. The intention is that as the barrel wears you can use a graded piston.
Bores do wear to the point they need re plating. A replate if no damage to bore is about 160 depending on size. Done by specialist.
Bores can wear quicker with open mouth carbs, how they are used and maintained, oil quality to name a few. Regular ring replacement is important on nicosil.
21yrs old, uts had a good inings. Id consider a new kit which is quickest solution of replate and new piston.
Whatever your route always gap the rings.
Malossi do sound noisier than standard.
As said make sure head is correctly modified
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