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RE-ringing pistons or not?


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Hi, just removed my cylinder head to have valves and seats re cut and valve guides replaced if ncessary to get performance up a bit.

Pistons are standard, with a minimal lip at top of bores.

What are your views on re-ringing the pistons with a set of cords rings to give a touch more compression?

looks simple enough or is it a waste of time. 

thanks steve

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obviously ideally you'd measure bores and pistons and assuming everything in spec and good condition then I'd hone it and ring it. did you compression test or leakdown test before you took it apart?

you need to be very careful honing with the crank in place so loads of time covering up etc

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5 minutes ago, hot-growler said:

did leakdown quite a while ago and got quite a bit of loss which I vaguely reember pointing to bores as noise could be heard through engine filler hole. think that could have been rings/bores

yes. realistically you'll find it needs a rebore but if you are adamant that you don't want to go that route then a bit of a glaze bust and new rings. depends what you are trying to achieve really, seems like you aren't keen on taking the engine out. 

 

All a bit odd though as you mentioned taking the head off to recut valves and seats (not due to head gasket failure). Not sure why you would do that when you have already self-diagnosed a bottom end problem

Edited by mtrehy
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I don't mind taking engine out, got facility and space to do it., but don't want to spend un-necessary funds when not needed.

On other hand don't want to scrimp as I can't ever think of selling it.

My view is that if I can up my compressions for say £50 by putting new rings in, Then I could hold fire for a re-bore if performance is not acceptable.

Sensible  or am I being a cheapskate?

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1 minute ago, hot-growler said:

I don't mind taking engine out, got facility and space to do it., but don't want to spend un-necessary funds when not needed.

On other hand don't want to scrimp as I can't ever think of selling it.

My view is that if I can up my compressions for say £50 by putting new rings in, Then I could hold fire for a re-bore if performance is not acceptable.

Sensible  or am I being a cheapskate?

wasting time and money then. Do it right now. you need to get measuring. 

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I'd measure bore ovality next. If a rebore is not needed then I'd refit head and give it an Italian tune-up to free gummed up rings. Leave diesel or ATF to creep down the bores while head if off should also help free off rings. Peter

Edited by Peter Cobbold
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Give it a good hone which might remove a gum/deposit line  and then get it measured to see if it is in tolerance.

If it is a genuine ridge caused by wear below, that you can feel at the top of the bore, then realisically a rebore is going to be required.

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On 8/24/2020 at 6:33 PM, Andy Moltu said:

If it is a genuine ridge caused by wear below, that you can feel at the top of the bore, then realisically a rebore is going to be required.

+1 to that. If you re-ring and it really is a wear ridge, you run the risk of breaking the new rings on the ridge.

 

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1 hour ago, JohnC said:

+1 to that. If you re-ring and it really is a wear ridge, you run the risk of breaking the new rings on the ridge.

 

That's why you fit rings with a "ridge dodger" shoulder on the top edge, about 10 thou less than the bore dia it allows the piston to reach it's maximum available lift and the piston ring still to miss the ridge whilst giving you max compression. Available  through many ring suppliers, these engines will easily accept rerings and if the ring manufacturers make ridge dodgers they accept that the bores have a degree of wear and they are happy their rings can cope with that.

We used to fit them regularly back in the days when the TR was the only car and at about 100k lift the head and rotate the liners 90 deg presenting a fresh face to the thrust forces of the piston (the ridge is only on the one thrust side). As Moss said in one of their brochure presentations doing this repeatedly until the ridge is present around the circumference allows "reasonably high mileage to be achieved." When a ridge dodger wasn't available I'd dress the grinding wheel and taking the top ring grind a 45 degree angle  on it's top edge, shady tree engineering which allows the continuing use of the car. You can't go berserk with this application because when the piston ring tilts in it's groove you still need a square face to be presented to allow full sealing but I can do it so I reckon others can too.

Mick Richards 

Edited by Motorsport Mickey
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  • 3 weeks later...
1 hour ago, AarhusTr6 said:

Hi

I am going through a similar winter project, ie top end re-build, how do I do the measuring spoken of?

Richard

 

You have to use a telescopic gauge then mic up the probes with micrometer. It is best to zero the telescopic gauge on an un worn part of the bore as you can then quickly see the ovality of the bore as you put it into the worn areas. But of course  you can use a bore DTI if you have access to one? You are getting into the realms of toolmaking inspection?

Bruce.

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Buy or have a loan of a set of "snap guages" (telescopic cross tube gauge with a vertical handle which goes "snap" opening to full width, hence the nick name) and a Micrometre which will cover the dia of your bores and piston diameter. You could use an internal micrometre but access to expand it will be tight and difficult to be consistent.

Remove one piston and con rod from the engine (on a 4 cylinder the rear cylinder gets hottest and wears most) and measure the cylinder bore diameter at the bottom of the cylinder sleeve at the area swept by the piston rings at their bottom most travel of their stroke. Measure across the centre of the cylinder (the telescopic gauge is "crowned" or lightly curved upon it's outermost ends of the measuring anvils, and so does a degree of self centering). 

Normally I expand the gauge by hand and lock it by the friction spool at the end of the gauge ( lightly, it needs to be able to slide) about 1 mill or so more than the dia of the cylinder before placing it inside the bore and selecting the area to be measured. Then keeping the gauge centered by eye in the bore rotate the vertical handle of the gauge along the axis of the telescopic expanders until the handle just reaches vertical and the compression telescopic movement becomes stiff (maximum expansion of the telescopic area). Then continue a few more degrees and then the snap gauge will become loose, (the telescopics have passed the maximum expansion and the curved ends now give you clearance). Tilt the telescopics carefully out of the engine bore without catching them excessively on the sides and measure the expanded gauge with the exterior micrometer, across the radiused highest spot ,that's your bore diameter at it's most worn area.

Do this a couple of times and compare the readings, these readings depend upon operator skill in "feel" of the bore with the "snap gauge" and the micrometre when you read it off . It will only take a few practice operations before you get a feel for the high area and the measuring drag on gauge and on micrometer to achieve high accuracy (within 1/2 thou easily achieved).

For the pistons remember they are made oval and so you need to measure around the skirt and high crown area to define your measuring directions. It's not difficult, the largest dia achieved is the area to be measured. Use the same micrometre used previously and write down the dimensions, compare against the cylinder bore dimensions and there are your dimensions to compare.

Mick Richards   

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Hi Steve,

Last year did the same thing your proposing.  Head professionally rebuilt, then I installed new (Hastings) rings and hone of the cylinders.   I also installed new rod and main bearings (standard size).   Did this as I took a stock NA head (7.75 to 1) and installed a spare PI head I had (9.4 to 1) and have heard the lower end needs help if bumping up  compression.   Wrapping the crank with plenty of plastic wrap kept it all safe.   While the head was off and engine still in the car, I was able to flush large amounts of sand casting from the block that had blocked the drain, so freed up some cooling flow as well.

All in all, not too bad of a job and the car has run well since.   A friend  called this a hill billy rebuild.  I guess the name fits, but it hey, it works.

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15 hours ago, YankeeTR5 said:

Hi Steve,

Last year did the same thing your proposing.  Head professionally rebuilt, then I installed new (Hastings) rings and hone of the cylinders.   I also installed new rod and main bearings (standard size).   Did this as I took a stock NA head (7.75 to 1) and installed a spare PI head I had (9.4 to 1) and have heard the lower end needs help if bumping up  compression.   Wrapping the crank with plenty of plastic wrap kept it all safe.   While the head was off and engine still in the car, I was able to flush large amounts of sand casting from the block that had blocked the drain, so freed up some cooling flow as well.

All in all, not too bad of a job and the car has run well since.   A friend  called this a hill billy rebuild.  I guess the name fits, but it hey, it works.

Hi . sounds good to me!  So you swapped out the US Spec head for a high comp PI head - am I right?  I have a slightly lovely . . but lack lustre US TR6 and would like a bit more ooomph.

 

BTW I have a CF Engine but in a CC body!

Rich

 

Edited by AarhusTr6
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4 hours ago, AarhusTr6 said:

Hi . sounds good to me!  So you swapped out the US Spec head for a high comp PI head - am I right?  I have a slightly lovely . . but lack lustre US TR6 and would like a bit more ooomph.

 

BTW I have a CF Engine but in a CC body!

Rich

 

If you have a US spec engine and want more oomph, get a copy of Triumph competition preparation Manual TR250,TR5,TR6. ISBN 978-1-78318-001-1.It tells you exactly what to do on USA heads to bring up the compression, SAH used this booklet to develop their special tuning kits in the 1970's for BL. Also I used this booklet as a guide for my 1973 TR and my car goes!

Bruce.

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