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maximum allowable runout for an 1147 cc engine

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gt350mk Marc Kay
Aurora, CO, USA   USA
Hello All,

I can't seem to find anything depicting the maximum allowable run-out for the cylinder bores for the 1147 cc engine.
My car came in a box with many projects completed on the car and some not. To make a long story short I think the engine was not run much in its life. However the current pistons are pitted. I got a neat set that have two compression rings and two oil control rings (the second one right above the king pin) that I would like to use. From observation and some real quick measurements it doesn't appear the motor is heavily worn. I think the previous owners were not versed in parts selection and threw in some used, better-than-nothing pistons. I would like to know before using this sweet set of pistons. I found one document stating that the cylinders should not be any more than 0.006 runout/taper/ovality, but that could have been just industry best practices. Would someone please push me in the right direction. I also just got a Fowler Dial Bore Gauge, that measures down to 0.0005. Also any instructions on how to set up the dial bore gauge for repeat-ability would be highly appreciated.

One last thing: form what I have gathered so far on these engines (at least the 1147 and 1296) is that they can withstand a beating before an overbore is needed.

Thank you all,
Marc

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Tonyfixit Avatar
Tonyfixit Tony M
Duncan, BC, Canada   CAN
Later today I will pull out my Triumph manual. But honestly, I would take all the measurements and talk to the guys at Hastings (piston rings) some rings are available that can tolerate oval and barrel worn bores better than standard rings.

I seem to remember something in the back of my mind about those pistons you have. I belive it was an advisory not to fit all the rings! I may well be wrong. I'm sure others will chime in on this.

Wolfcreek Steve Steve P
Central, WI, USA   USA
Just my personal point of view, but "What can I get away with?" isn't a good mindset when building an engine you care about!

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clshore Carter Shore
Beverly Hills, FL, USA   USA
There were some replacement Hepolite pistons that featured two oil control rings, one above the pin and one beneath it.
The logic was apparently that this would allow replacement into worn bores without honing, avoiding excess oil consumption.

Back to your question, bore ovality is seldom the issue, it's bore taper that is most common wear.

Your dial bore gage has to be calibrated against some standard ...
A ring gage is nice, but an accurate micrometer or caliper will do in a pinch.
Fit the gage anvil for the measurement range you desire, set mic/caliper to a fixed distance and lock it.
Now place the gage in the gap, steady it to align, and zero the dial pointer and lock it in place.
Remove the gage, then fit it back into the gap to double check the zero setting.

This is easy if you have 3 hands; many folks will gently clamp the bore gage in place so that they can
easily manipulate the mic/caliper and zero the dial pointer at the same time.

gt350mk Marc Kay
Aurora, CO, USA   USA
Thank you for your response.
Question: do I set the caliper or mic to the diameter of the cylinder bore I wish to measure, example, 2.8218 inches. I set up the bore gauge with the anvil to 3 inches, for example. I then measure the cylinder in question. The dial bore reads, for example, 2.7912. Is that the actual diameter of the cylinder, 2.7912? OR would you expect the bore gauge to read, for example, 0.0135? Then, for example, I would subtract 3 inches from 0.0135 which equals 2.9865 and the 2.9865 is the actual diameter of the bore for which the gauge was placed? I think I am confusing myself will all of the YouTube videos on the topic. The first day I had it, I tried it out and it showed, for what I interpreted as 2.1718 inches. I tried the same site for all 4 cylinders and they were all very close to one another, which I interpreted as good being there was no single cylinder much smaller or larger than the rest.
I want to get the car put back together so I can start testing it. It's got new suspension, steering, brakes, etc, of which a road test is necessary, especially if I am to drive the car fast. One day I woke up, remembered when I was in high school and came down with the British bug, and what a perfect entry level sports car! I am sure lots of us would like a Lotus, XKE, or other European sports car, but the little spitfire comes with everything they have, for the most part, that is except for a neck snapping, tire burning engine. Albeit the car makes up for lower horse power with great handling, plus they look sweet.

Has anyone else improvised a bit on the engine just to see how she'd perform, saving for the day when you could spend thousands of bucks on a little screamer? My back is also getting bad and I don't want to be laid up with my poor spitfire still apart.

Thank you all,
Marc Kay

gt350mk Marc Kay
Aurora, CO, USA   USA
I totally agree. I actually will have an obsession knowing the bores are not as perfect as a Sunnen overbore mill can make them or a resleeve would make them. I have super limited time as my father got super sick in 2013, lost his limbs and part of his colon and so I have to help out my mom with his care. Also I think if he could go for a drive with me it would cheer him up since he likes spitfires too and wanted a 1965/66 since he was in college when they were new. He had an English Ford which his mother would allow...

Thank you,
Marc Kay

gt350mk Marc Kay
Aurora, CO, USA   USA
Thank you. I will give them a ring, no pun intended. Further more has anyone ever seen piston rings available (that don't have to be custom made) that have no ring gaps, like Total Seal produces. My father said something about British cars needing to use Perfect Circle as stock rings were a common source of problems, however he can't recall who made the stock ones. I think there were a lot of bad write ups on some British cars in the 60s and 70s that put a stigma on those cars. I don't know as my experience is with U.S muscle cars, especially the small Ford v8 of which there is a million times more options than on British cars. Even the small Windsor had it's issues, however not as many I think. I have seen 289 and 302s that were beaten and abused and had very little wear if any, even if oil changes were sporadic. I have two in my garage.

Thank you,
Marc Kay

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Wolfcreek Steve Steve P
Central, WI, USA   USA
If you want to measure taper or out of round, you don't need a ring gauge. Put the bore gauge anywhere in the bore, zero it, then move it around to find the largest measurement, re-zero the gauge. Now move around until you find the smallest dimension, bingo the difference in the two numbers is your taper. I've always heard .003 taper is max, anything over that will fatigue the rings quickly and fatigue causes cracks. (doesn't matter if Triumph or Cummins Diesel, taper is taper, rings are rings. if anything larger bores will accept more taper.)

gt350mk Marc Kay
Aurora, CO, USA   USA
Thank you for the response.
Allow me to be certain of your excellent recommendation:
1 zero out bore gauge.
2 take reading of top of cylinder or where the rings would travel no more
3 zero out gauge again
4 take reading at bottom of cylinder
5 subtract the first reading (top of cylinder) from the second reading (bottom of cylinder)
6 I now have a run-out reading which will show if I'm able to use engine as is or have to take to machine shop or special rings.

I once worked for a thief that advertised he would professionally rebuild an engine (mostly Ford 302s). He removed lifters, push rods, con-rods with pistons and never numbered since he only took apart the engine, cleaned it out as much as possible in a day and throw everything back together without keeping which component originated from, like number one piston and rod go back into number one cylinder. I was surprised how well the engine ran. He never measured anything. The engines ran great. They didn't wobble at all and pulled strong. He even threw an engine into a truck which he attempted to repair the crack in the block by FCAW, which failed miserably. However the engine ran great. How, why? (I only worked for the creep for two weeks of which I was never paid and was a material witness for criminal proceedings so I don't want anyone to think I was in cahoots with the pig). Sorry this got way long.

Thank you,
Marc

I have forgotten my auto mechanics 101.
Question: if the cylinder is beyond specification or even very close to it, why would the rings crack, maybe even piston or block? Is it from piston slap or is it because the rings compress then decompress rapidly, whereas they should not really expand or contract at all?
Also I would imagine that there might be enough blow by to contaminate the oil and or push it out of the sump? Would this last question be the result of severe run-out?

Thanks again

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Wolfcreek Steve Steve P
Central, WI, USA   USA
First of all, please don't use the term "run out" for what you are trying to express. Run out is wobble in a shaft. the term to use is "bore taper", or just taper as we know it is a bore.

Taper will break the rings by fatiguing them from the constant expansion/contraction each revolution. A piston ring is a spring, but it is only meant to expand/contract a very small amount. a spring's life is distance squared X cycles, so more distance= less cycles. (this is a crude equation, but in the ballpark)

There is no zeroing until you put the gauge in the bore, once it is in the bore, you are trying to find the largest place, (yes, it is usually at the top of the ring swept area) but don't be afraid to check many times up and down the bore. (and I always check with the gauge parallel to the crank, then 120 degrees off each way so as to find any eggyness in the bore. Once you have found the largest reading, zero the gauge, then start over looking for the smallest reading. That smallest reading will be the total taper and/or eggyness. this is strictly a comparison measurement, it has nothing to do with actual bore size. (Which tells you what size piston you will need)
Checking for taper/eggyness will tell you if the cylinders need to be bored/sleeved which should be your first order of business, secondly if the bores are within taper specs, you must compare bore size with your piston size, so you will know if you can use these pistons. Being aftermarket parts, the pistons may or may not use the same clearance specs as the stock factory pistons.

Born Loser Avatar
Born Loser Silver Member Matthew Taylor
Land O Lake, FL, USA   USA
In reply to # 1506124 by gt350mk Thank you for the response.
Allow me to be certain of your excellent recommendation:
1 zero out bore gauge.
2 take reading of top of cylinder or where the rings would travel no more
3 zero out gauge again
4 take reading at bottom of cylinder
5 subtract the first reading (top of cylinder) from the second reading (bottom of cylinder)
6 I now have a run-out reading which will show if I'm able to use engine as is or have to take to machine shop or special rings.


You will probably find many different methods for this. I agree mostly with what Steve has posted above. But, in my opinion - one difference. There are 3 things you need to know:
1) Tapper
2) Out of Round (eggyness)
3) Excessive wear (worn out cylinder)
Its my opinion that these 3 things need to be evaluated independently.

As a rule, I always take 3 readings for every evaluation - Like Steve mentioned, aligning the bore gauge to the crank is a good point of reference, then 120 deg each way (roughly, dont go crazy getting it EXACTLY 120.000 degrees). Record all 3 readings, with their respective rotation - example: 3 columns: 0, -120, +120. Or: Crank, left, right. You get the idea, whatever keeps it straight for you. In addition, take 3 readings up and down as well - Top, Middle, and Bottom. Thats 9 locations you are going to measure.

Second rule - take EACH reading 3 times. Average the 3 readings (or discard an obvious way out reading) for the final reading at that location. This might seem excessive, but with extremely precise instruments, not measuring in EXACTLY the same spot, you will quickly see why this works. Record these readings in the rows under the columns above. Dont forget to leave a 4th row for the average final reading. Assuming you are going to at least hone the bores, I would make a small Sharpy mark at each spot you plan to measure at, so you can get real close to the same spot each time. Or a dab of tape, and read right under it. Or whatever you come up with that works for you. Thats 9 locations times 3 readings each = 27 times in and out with the bore gauge.

Third Rule - of all the methods below, your final answer is the LARGEST of all the comparisons. In other words, when you follow my advice below, you will have 3 tapper readings. When evaluating how much tapper you have, discount the 2 smaller readings, the WORST is what you consider, so the LARGEST difference.

1) Tapper - this is a comparison of like columns - what I mean is dont look at the "-120" degrees at the top, and compare it to the "+120 degrees" at the bottom (likely the largest difference on your sheet). Instead, compare the "-120" at the top with the "-120" at the bottom, and likewise for the other 2 readings as well. This will give you the true tapper, and not combine the tapper readings with your "eggyness" at the same time.

2) Out of Round - this is a comparison of like rows. Compare the 3 readings to each other for the TOP, Middle, and BOTTOM.

3) Bore Wear - So for this one, you dont need the differences, you need an actual measurement. You can take the actual measurements (how I would do it), and record them on the sheet as mentioned above - then do the math, or just record the differences, as Steve says. If you use Steves method, you will need to take new readings for Bore Wear. If you use my method of recording the true values, and then doing the math seperate, just look at your sheet and find the largest FINAL bore reading you have (the average of the 3 readings you took at that location).

The last thing you may want to consider is the maximum expansion/contraction of the ring. With all of the readings you have taken, its an easy calculation. Average each final reading for each row (top, middle and bottom). Then find the largest difference. That will be how much the ring has to move in and out on each stroke.

Above, you seem to be a bit confused about your bore gauge readings. Carter mentioned you need to calibrate it the first time. You can use that same method to straighten out your brain when you get confused! Just set your calipers to 3", and then read the "inside" feet (or what ever you have). It should read exactly 3".

Hope that helps!



Matthew
1960 Triumph TR3a
1970 Triumph Spitfire MK 3
2012 Mini Cooper SS Convertible
2018 Jaguar F-Pace



Edited 4 time(s). Last edit at 2018-01-06 10:26 AM by Born Loser.

Lizzard d id
san jose, CA, USA   USA
Are these standard size bores and pistons ? You have to assume the bores were done correctly when they were done , then they "wore" , that wear will show as a "ridge" at the top of the cylinders . Do your cylinders show a ridge ? If so how large is the ridge ?

gt350mk Marc Kay
Aurora, CO, USA   USA
Thank you for your your response.
The cylinders and pistons seem to be oem size, that is no one has machined the block to date. There seemed to be a ridge on number one and four piston that grabbed my finger nail so I used a ridge reamer to remove them, however I think it was just coke, or a carbon deposit that has seen intense pressures and temperatures. The ridges came off easy and according to my dial bore gauge all areas were real close to one another in the area where the ridges were.
Currently I would like to get the engine running so I can test the various systems and troubleshoot them and I think Nitin would cheer up my father who has suffered a horrible health incident 5 years ago, whereas he can no longer drive. Both if us like the Triumph Spitfire.

Thanks again
Marc

Lizzard d id
san jose, CA, USA   USA
In reply to # 1506226 by gt350mk The cylinders and pistons seem to be oem size, that is no one has machined the block to date.
That's good news the stock bores were done well at the factory , imho .

In reply to # 1506226 by gt350mk There seemed to be a ridge on number one and four piston that grabbed my finger nail so I used a ridge reamer to remove them, however I think it was just coke, or a carbon deposit that has seen intense pressures and temperatures. The ridges came off easy and according to my dial bore gauge all areas were real close to one another in the area where the ridges were.
A ridge reamer isn't for removing carbon . Not that it matters now but the carbon is removed with a hand held knife so that the metal isn't removed and the the ridge can be inspected . That way the height of the ridge can be seen "naked" sans carbon .
It sounds like your block / cylinders are ok , any ridge they had is now gone and removing the ridge didn't take much effort . The low effort leads me to believe that you didn't cut into the metal much if at all .

Have you put the pistons into the cylinders without the piston rings ? If so how did they feel ? Nice no looseness feel without binding ?

gt350mk Marc Kay
Aurora, CO, USA   USA
Thanks for responding. I have only removed the cylinder head, thus far. Another clue is that the lifter bores are tight, not easy to pull out the lifters, but nothing a magnet won't help. I know this is not scientific, nor with good solid numbers, but with the time I have, not shabby. The push rods look great. There is noticeable wear on the end of the rocker arm. Lots of heresay evidence on the bright side. Thank you for your time.

Thank you all for your time.

I have to weld in a rear wing and pan assembly on an old mustang before I can pull anything else on the Spitfire, however I do have an hour or so when ever I am working on the 'stang.

Have any of you removed taper via a finishing stone? I am not condoning this at all since there is no control and would seem to me to enlarge the entire problem. Any other experiences?

Thank you,
Marc Kay

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