cylinder tolerences
Moderators: John@sos, charlesp, Charles uk, RickUK, Petergalileo
cylinder tolerences
My my service manual for a Tc 102 shows a cylinder tolerance of 2.237/8 " yet when I measured it I made it 2.235". Am I reading this correctly? What is the manufactured size?.. Cheers!
Re: cylinder tolerences
First thing to do is a visual check, is there a step at the top of the bore? Are there any sunstantial scores running up and down the bore? After that if are measuring to the nearest thou what are you using to measure? Is it calibrated and repeatable?
The most wear is likely to be around two thirds the way down the bore. If you are getting that size in that area I'm sure it will be fine. Seagulls are low compression low tune engines, and dont seem to wear out bores very often, I suspect the high oil mix and low RPM helps, plus the often lowish usage an outboard gets. Perhaps treat the old lady to some new rings and away you go
Finally try the piston in the bore, if it is not moving around sideways like a piece of gentlemans anatomy in a shirt sleeve, then it will be fine!!
The most wear is likely to be around two thirds the way down the bore. If you are getting that size in that area I'm sure it will be fine. Seagulls are low compression low tune engines, and dont seem to wear out bores very often, I suspect the high oil mix and low RPM helps, plus the often lowish usage an outboard gets. Perhaps treat the old lady to some new rings and away you go
Finally try the piston in the bore, if it is not moving around sideways like a piece of gentlemans anatomy in a shirt sleeve, then it will be fine!!
Re: cylinder tolerences
thanks oyster, I think it must be good then. I bit of servicing and it will be good for next season ! cheers!
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Charles uk
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Re: cylinder tolerences
How are you measuring the bore?
Make it idiot proof and someone will make a better idiot.
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headdownarseup
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Re: cylinder tolerences
As a "hillbilly" way i place a piston ring into the top 2 thirds of the bore and measure the ring gap with some feeler gagues.
Measure in at least 4 places along the bore to get an average, then refer to the manual for max. limits on wear.
If you can get anywhere close to 50 psi of compression out of it, it'll do ok but stay with 10:1 fuel mix.
Any less oil in the mix and they don't like it much.
Jon
Measure in at least 4 places along the bore to get an average, then refer to the manual for max. limits on wear.
If you can get anywhere close to 50 psi of compression out of it, it'll do ok but stay with 10:1 fuel mix.
Any less oil in the mix and they don't like it much.
Jon
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Charles uk
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Re: cylinder tolerences
Jon's Hillbilly method is almost spot on!
It's very difficult to measure the ring gap with the rings with the diagonally scarfed ends, the later rings with the square ends work much better, the 2 locations used for measuring are 1/4" above the very base of the of the cylinder (Least wear area) & 1/4" above the exhaust port ( highest wear area), slide the ring into position using the skirt of your piston to ensure the ring is perfectly square in the bore, which was cleaned with a paper towel, no oil, use the same old ring for both measurements, take care not to let the ring ends slide into any of the ports.
In the low wear area depending on the ring your reading will be 10 thou ish + or - a few, & a little more in the high wear.
The sparkplug end of the cylinder is regarded as the top.
It's very difficult to measure the ring gap with the rings with the diagonally scarfed ends, the later rings with the square ends work much better, the 2 locations used for measuring are 1/4" above the very base of the of the cylinder (Least wear area) & 1/4" above the exhaust port ( highest wear area), slide the ring into position using the skirt of your piston to ensure the ring is perfectly square in the bore, which was cleaned with a paper towel, no oil, use the same old ring for both measurements, take care not to let the ring ends slide into any of the ports.
In the low wear area depending on the ring your reading will be 10 thou ish + or - a few, & a little more in the high wear.
The sparkplug end of the cylinder is regarded as the top.
Make it idiot proof and someone will make a better idiot.
Re: cylinder tolerences
I am using a vernier caliper, which of course only measures a short way up from the bottom of the bore; so I adapted a pair of dividers , inserted them ( repeatedly) and then measured them with the vernier. Not ideal, but I got a fairly consistent 2.236/7 " reading. Interestingly there were a few scratch marks on the piston but not in the bore. everything else looks pretty good so far.
Re: cylinder tolerences
I posted the last reply before I saw the other info regarding measuring the piston ring gap. Thanks to you all for your help!
PS. Is the 2 jet carb as used on the TC 102 the same carb as the 46n 3A ? they look similar. ?
PS. Is the 2 jet carb as used on the TC 102 the same carb as the 46n 3A ? they look similar. ?
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Charles uk
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Re: cylinder tolerences
Just the vernier should be good enough for the low wear area, then you will know the diameter there, now do the ring trick in the same place & measure the ring gap.
Pye D will give you the circumference of the ring with that size feeler gauge in it, now measure the high wear area with the ring trick, now divide your slightly larger circumference by Pye & you've got the bore in the high wear area.
Seagulls are not famous for bore wear & the reason you not getting an answer on your carb question is probably the same as my answer "I don't know".
Pye D will give you the circumference of the ring with that size feeler gauge in it, now measure the high wear area with the ring trick, now divide your slightly larger circumference by Pye & you've got the bore in the high wear area.
Seagulls are not famous for bore wear & the reason you not getting an answer on your carb question is probably the same as my answer "I don't know".
Make it idiot proof and someone will make a better idiot.
Re: cylinder tolerences
Thanks " Charles UK " for your advice , I will have a go. As far as the carb is concerned ; I will find the answer and let you know! All power to Brits! ( engines)
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headdownarseup
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Re: cylinder tolerences
Let's have a look at your carb in question. Any pics?
My tuppence worth
Jets are a bit more important than outside appearence of the carb. All depends on how authentic you'd like to be with your 102. Yes there are some very subtle changes to these carbs over the years, none in my opinion that would improve or worsen the engine's overall performance. They all have the same bore diameter, some have very slightly longer throttle slides (2mm difference in length is what we're talking about here) some have "lumps" that do absolutely nothing at all, some have a removable throttle slide "guide" and later ones have a rivet that replaced the original removable guide. They all come apart the same way, and they all corrode in exactly the same way.
Inlet cowls change over the years, i must have seen a few different variations of these by now on all different variants of 46n carbs.
Jets for your TC (in an ideal world) should be kept at the older 10:1 setting. Again some very slight variations with these, nothing too drastic to worry about but in order to see what you've got in there in the first place you're going to have to remove those bad boys out of there just to make sure it's what it says it is. WORD OF WARNING here. The banjo bolt that holds the bowl to the main body of the carb corrodes like a really corroded thing!!! EASY DOES IT. If you end up stripping the thread in the bottom of the carb body due to the corrosion then all is not lost. Helicoils can cure a multitude of problems in this area. John offers a reconditioned carb already heli coiled. Worth checking out before you put a spanner to this.
Pics will help me a bit more
Jon
My tuppence worth
Jets are a bit more important than outside appearence of the carb. All depends on how authentic you'd like to be with your 102. Yes there are some very subtle changes to these carbs over the years, none in my opinion that would improve or worsen the engine's overall performance. They all have the same bore diameter, some have very slightly longer throttle slides (2mm difference in length is what we're talking about here) some have "lumps" that do absolutely nothing at all, some have a removable throttle slide "guide" and later ones have a rivet that replaced the original removable guide. They all come apart the same way, and they all corrode in exactly the same way.
Inlet cowls change over the years, i must have seen a few different variations of these by now on all different variants of 46n carbs.
Jets for your TC (in an ideal world) should be kept at the older 10:1 setting. Again some very slight variations with these, nothing too drastic to worry about but in order to see what you've got in there in the first place you're going to have to remove those bad boys out of there just to make sure it's what it says it is. WORD OF WARNING here. The banjo bolt that holds the bowl to the main body of the carb corrodes like a really corroded thing!!! EASY DOES IT. If you end up stripping the thread in the bottom of the carb body due to the corrosion then all is not lost. Helicoils can cure a multitude of problems in this area. John offers a reconditioned carb already heli coiled. Worth checking out before you put a spanner to this.
Pics will help me a bit more
Jon
Re: cylinder tolerences
As you say, not much difference between the 2 carbs; after a bit of a search on the net I found that most of the part nos. are the same. However, my 2 jet seems to be ok on the threads, so I think maybe I am lucky.