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Engine seizes when hot


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HI,

I rebuilt my TR3a engine with new liners (larger ), new pistons and rings, bearings etc. When cold it turns over and starts beautifully. However if you go out for a 30 min run (water temp 85c-90c ish, the weather being quite hot) and then stop and turn off the engine, leave it 10 mins you can't restart because it has seized. Leave it longer and it'll start again.

I admit I have probably only gone two or three hundred miles since this rebuild, but it's showing no sign of improving.

Do I just need to do more miles, or do I need to take the head off and roughen up the bores ?

And if I don't need to do that on a new car why do I have to on the TR?

 

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Hi Jock,

before you start roughening anything you need to know what it is that is seizing.

It could be Piston/Liner or crank main or big-end.

I'm sure there will be wear marks somewhere. You need to find them.

I would also suggest that roughening anything will not stop a seizure - wrong size something or the other

 

Roger

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Heat related seizure is an extreme heat related issues 

I had this on a 2 stroke bsa bike and it was the piston rings not gapped properly 

it would start and run ok after being left to cool. 
 

but doesn’t really answer why it seizes when stopped rather than locking everything up when running ?!

as Roger says you need to open it up and look for telltales 

just my 2 penny worth you understand. 
Motorsport Mickey will know .

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Ring gaps would be the first thing I would suspect. Did you check them on installing? The block etc is acting as a massive heat sink when turned off perhaps causing the seize.

 

Iain

Edited by iain
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Perhaps an obvious question but why do you say the engine is seizing, I’m guessing because you push the starter and it doesn’t turn over , but is it the starter failing to turn the engine , for a reason other then the engine has seized? 
 

ATB Graham

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Sluggish starter would be my first port of call given the proximity to the exhaust manifold. Which starter is fitted ? the od Lucas type are prone to issues and although seem to work fine on the bench fitted is a whole different ball game.

1, On stopping after the 30 mins run, disconnect or isolate battery, grasp the fan (after shutting the engine off) and try to turn the engine. if it turns over then check the flange joint for the starter to engine and that it is even no gaps (misaligned )

2 Does the engine sound different towards the end of the run? if so what is different.?

3, Does the oil pressure fluctuate much hot to cold, what is oil pressure hot?

Rgds

Rod

Edited by Rodbr
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I’d side with Iain regarding ring clearances.
 

Starting from cold with ring clearances which are problematical ( less than maybe 13 thou...I’m not sure because I never run that tight ! ) would be achievable. Also whilst the engine is running the rings are being drenched quite a few times per second with a petrol mix (V cold) which does a pretty good job of cooling the rings and helping prevent them “ butting “ up expanding their dia and seizing the pistons. Leave the engine for a few minutes when warm and the heat sink will expand the rings butting them up and the grip of static rings will exceed the starter motor torque. Leave it go cold and “ viola” the piston ring diameter reduces and the engine clearances return and it will start.
Make sure the piston to liner clearances are to factory workshop manual dimensions ( 3 1/2 thou from memory, I forget I never run them that tight, I’m happy at 4 1/2 - 5 thou) and remember pistons aren’t round, measure them in  hot cross bun pattern across both ways.

I would NEVER run the compression top ring at less than 15 thou and 20 doesn’t scare me, as for the second ring in the labyrinth seal maybe 3 thou bigger... who cares it doesn’t make a negative difference to the compression and Power.

Mick Richards

 

Edited by Motorsport Mickey
Typo, 30 rather than 3 ! for second ring
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There is a guide for ring gaps I think from memory the top/compression ring is 4 thou per inch of bore and second ring 5 thou per inch of bore 

when I replaced my liners for 89mm ones I think I set the top ring to 14 thou and the second at 18 thou

Chris

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Yeah, those are guides Chris but other opinions and from better qualified personages than myself exist.

http://diagnosticengineers.org/journal_ articles/Ring Gaps vs Knowledge Gaps.php

To cut to the chase ..."This knowledge was commercial dynamite because, instead of the '0.015”/0.018” spec., it meant that new rings with gaps over 0.018” could be used without any detriment to the engine's performance.  The gap was only detrimental when it was the result of peripheral wear. "

Mick Richards

Edited by Motorsport Mickey
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First, thanks to you for your comments and tips. The engine cannot be turned by hand on the fan. The oil pressure hot at, say, 2200rpm is 60-70psi. So no problem.The starter is a hi-torque modern starter. You can unjam the engine by bumping the car, even by one person on a flat road. So not truly seized, just sort of nipped.

I think I would have melted any white metal bearings if they were the problem. So that leaves the piston rings. Are you really saying that I needed to file or grind the ends of new piston rings bought with the new pistons. I never worked in a car factory but i'm pretty sure no one is hand fitting piston rings in modern car engines and I assume the pistons and rings are being made the same way for TR's as for any other car.???

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It's normal practice when building a classic engine to check the piston ring gaps and file the ends to adjust if necessary. Can't speak for modern engines as I've never built one.

I've built two engines in the last 5 years, both Triumph sixes. And with both engines, the rings were correctly gapped straight from the box, needing no adjustment. 40 years ago, building a BMC A-Series, I can remember needing to file the new piston rings.

Nigel

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I don't think you can compare modern production methods & tolerances with our old bangers.

All the Triumph engines I've ever built needed ring gaps to be checked and often adjusted.

Jerry

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"Are you really saying that I needed to file or grind the ends of new piston rings bought with the new pistons.... I never worked in a car factory "

Yes. Car factories are organised places, (especially todays new factories) there the components are assembled after being "batch engineered" where the pistons and liners are made in their many thousands by countless different suppliers, and the pistons and liners graded (in your workshop manual you'll see them graded F. G. H, (no I don't know why they didn't pick A B C).  According to the different fits between the pistons and liners when made (the tools wear when making many thousands of units, varying the final fit). With modern piston and rings the grading and fit will be very tightly controlled allowing machines to select and even take part in the ring fitting...that's not what we have.

We have limited runs of components making our pistons, liners and piston rings, the reduced numbers means our components need a degree of final fettling in case the tolerances vary as in with piston ring gaps. Almost any workshop manual gives instruction on the manner of measuring the piston ring fits and what is required (even though when these books were written these cars were amongst THE modern cars of the time) and so the same procedure needs to be followed for the piston ring gapping. Hopefully your piston ring gaps are correct...but it can't be assumed, I see you've replaced your liners and so the book which you used for reference whilst doing that will also have "gapping" of piston rings covered there.

Mick Richards  

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1 hour ago, jocklow said:

First, thanks to you for your comments and tips. The engine cannot be turned by hand on the fan. The oil pressure hot at, say, 2200rpm is 60-70psi. So no problem.The starter is a hi-torque modern starter. You can unjam the engine by bumping the car, even by one person on a flat road. So not truly seized, just sort of nipped.

I think I would have melted any white metal bearings if they were the problem. So that leaves the piston rings. Are you really saying that I needed to file or grind the ends of new piston rings bought with the new pistons. I never worked in a car factory but i'm pretty sure no one is hand fitting piston rings in modern car engines and I assume the pistons and rings are being made the same way for TR's as for any other car.???

Its always dangerous to assume that off the shelf parts for out TR's are ready to fit.......they rarely are and will need checking first. Another example is Cam followers. They most definitely need fettling to ensure they too do not stick through galling. Clearances on new water pumps and oil pumps also need to be checked. All part of the fun.

Iain

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1 hour ago, iain said:

Its always dangerous to assume that off the shelf parts for out TR's are ready to fit.....

Iain

Is a shame that the manufacturers and suppliers don’t make this clear at the point of sale. 

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There is a lot of detail that you need to know when rebuilding one of these engines. Ring gaps is just one of many. I think it is all covered in this forum but not all in one place.

Stan

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Agreed Stan, but unless you have a problem do you search for an answer?

Perhaps we should try to create a one stop fact sheet for individual subjects? 

Iain

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I noted when I bought my piston & rings with sleeves  ..as a kit quite recently - the component parts were made in different countries.  In this instance ; the sleeves were made in India and the rings were American.  I don't recall off the top of my head where the pistons were made. But the point is that they were only collected and packaged  as a set  in the UK.  And so although each part would be made to tolerance - there would be a degree of best or worse-case fit.   Accordingly I was interested to see how mine measured up.    

I haven't as yet checked the ring's end gaps, (And yes, I would do this as a matter of course) - but I did note that the pistons themselves varies in the brand new bores by a few thou, and that the tightest piston had only a 0.003" skirt clearance between it and the loosest of the four sleeves.  If that piston was fitted to the tightest sleeve then the gap may have been 0.002" or perhaps even a tad less.  I concur with Mickey in saying that three & a half thou is too tight and so two or even three thou would probably pinch up as you have describe. 

Certainly, once my engine's new liners are fitted - I will recheck the figures and then use a little emery paper to ease the piston a tad.   I prefer not to take anything off the bore.  Again as per Mickey ..  0.0045" clearance sounds good to me.

Pete.

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6 hours ago, foster461 said:

There is a lot of detail that you need to know when rebuilding one of these engines. Ring gaps is just one of many. I think it is all covered in this forum but not all in one place.

Stan

I was attempting something along these lines in my blog " That was a year that was..'   with the kind comment and help of you all,  but Covid stopped play and now I'm in the middle of moving house.  I haven't given up on the idea but I'm afraid it'll have to wait a little while.

Pete.

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