Cylinder liners

[roughground]

My block was rebuilt about 3 years ago. The crank was found to be still within original tolerance so was polished and new mains and big-ends fitted. I didn't check the bores but honed them and fitted new rings. The engine runs nicely but lacks that bit of zip one expects. Could I now have fitted new liners and reuse the almost unused pistons etc? I realise that it sounds a cheapskate way to do things but I want to keep my engine not swap it for an unknown recon.

[BlueTR3A-5EKT]

To get the replacement liners fitted and honed may cost not far off a set of pistons and a rebore to match. 
If your new rings were correctly gapped and the existing pistons were within tolerance I think you may need to look elsewhere for that zip you are missing.    
A PI knowledgeable person will be along in a moment.

[Motorsport Mickey]

.

Edited February 17, 2023 by Motorsport Mickey
Duplicate

[Motorsport Mickey]

11 minutes ago, Motorsport Mickey said:

"The engine runs nicely but lacks that bit of zip one expects." 

...One expects from what ? how worn is the engine ? unless you measure it on the bores and the piston diameters (they aren't round) you can't anticipate what likely result you'll get from the rering. The good news is maximum performance is NEVER delivered on a new engine or even an engine that is freshly bedded in, the engine needs to be 90% worn to deliver the best performance. When I build a race engine I open up clearances and anything that rubs on one another to reduce drag ..."and give it that bit of zip one expects" but you don't know at what position your engine is. 

What mileage have you on the rebuilt engine ?  Have you carried out BMEP* bedding in ? you are likely driving the equivalent of a new engine, ask me if you want to know how, ...and no, it doesn't include high revs.

Mick Richards

 

* Brake Mean Effective Pressure

 

[BlueTR3A-5EKT]

+1 for bedding in with BMEP technique

[FatJon]

Why liners? You can rebore to at least +60 thou and pistons are inexpensive.

A engine which runs well and doesn’t clank or smoke but has poor performance probably has fuel, timing or ignition problems. 

Edited February 18, 2023 by FatJon

[Waldi]

I assume you think/suspect the bores/tolerance?

Have you done a compression test, wet and dry?

Waldi

[roughground]

Hi Al;l 

Thanks for the replies. The engine has SUs and has had the compression raised to 9.5:1. the ignition and fuel are correct but the compression is down. I did a check and found all cylinders to be 125psi. It doesn't burn oil and pulls well but not as good as my TR7, hence the questions. The engine has run about about 3000 miles of non aggressive driving since the rebuild.

It sounds as if the rebore is the least painful option, trouble is find someone in Lincoln to do it

[FatJon]

A bit of a drive but Jonathan at Stanwood Engineering in Chesterfield is very reliable. He does all my machining on special engines .

[openroad]

Have sent you a PM , with a couple of options , reasonably local to you.

Cheers,  Conrad.

[stuart]

53 minutes ago, roughground said:

Hi Al;l 

Thanks for the replies. The engine has SUs and has had the compression raised to 9.5:1. the ignition and fuel are correct but the compression is down. I did a check and found all cylinders to be 125psi. It doesn't burn oil and pulls well but not as good as my TR7, hence the questions. The engine has run about about 3000 miles of non aggressive driving since the rebuild.

It sounds as if the rebore is the least painful option, trouble is find someone in Lincoln to do it

If its only done 3000 miles of in your words "Non aggressive driving" then Mick instructions are your best bet, its never properly been run in. I would do that before anything else.

If your in Lincoln then go over to Gainsborough and see Daryl at Racetorations.

https://www.racetorations.co.uk/

Stuart.

[Andy Moltu]

Ignore me - thought I was in the 4 cylinder forum.

Go on admit it.

You want someone to say swap to 89mm pistons and liners. (Misread and assumed I was in the 4 cylinder forum)

Check the rest of the set up first.

Tappets, ignition timing and mixture.

If these are all OK it might be worth checking the cam timing in case it was set up erroneously before.

[stuart]

1 minute ago, Andy Moltu said:

Go on admit it.

You want someone to say swap to 89mm pistons and liners.

Check the rest of the set up first.

Tappets, ignition timing and mixture.

If these are all OK it might be worth checking the cam timing in case it was set up erroneously before.

Err that would stretch a TR6 block a bit!

Stuart.

[Dave McDonald]

51 minutes ago, stuart said:

Err that would stretch a TR6 block a bit!

Stuart.

It certainly would, the block would look like a 6 circle version of the Audi car badge of overlapping rings. 
78mm max bore for reliable 6 cylinder block. 
Dave McD

[Andy Moltu]

Oops in 4 pot mode.

Distracted by liners in the title!

[Rob Salisbury]

Running on carbs  it's never going to have the get and go to the next county that a Pi has, also you've not mentioned any head work, maybe the somewhat low compressions are due to leaky valves, as Waldi says, do a wet and dry comparison test before taking anything to bits.

Let us know how you get on.

Cheers Rob

 

 

[JohnC]

From what you've said, I wonder if you definitely need to let someone loose on your block. Have you had the car set up on a rolling road? That way you would at least know you're getting the best out of what you have before committing to spending lots of money. Also, do you know what cam you have? Would be worth comparing notes with other owners running SUs.

J

[astontr6]

On 2/17/2023 at 9:34 PM, Motorsport Mickey said:

 

What is the BMEP technique?

Bruce.

[charlie74]

These two links make for interesting reading:

https://www.tr-register.co.uk/forums/index.php?/topic/50484-cylinder-bore-wear/

 

https://www.tr-register.co.uk/forums/index.php?/topic/81670-piston-rings-and-sizing/

 

[Motorsport Mickey]

28 minutes ago, astontr6 said:

What is the BMEP technique?

Bruce.

Brake Mean Effective Pressure

In the combustion cycle the most pressure is achieved upon the downward stroke of the piston on the power downward stroke (no surprises there). This pressure forces gas behind the piston rings into the piston ring slots and forces the piston rings outwards and into the engine cylinder walls gouging (steady, we are talking microns here) complimentary grooves into the walls with grooves in the piston rings. These grooves on the walls hold oil allowing it to be suctioned out as the rings pass allowing lubrication to the cylinder surfaces complimented by the maximum compression to be developed in the cylinder on it's upward compression stroke. There is a careful balance between enough oil for lubrication and too much oil which prevents the full expansion of the rings and upon a thousand miles or so of being burnished by the the oil sodden rings promotes ...glazed bores.

If you peruse the websites of "trophy car" owners there you will find "woe is me" tales of glazed bores mysteriously happening and the much monies a full strip down to hone the bores to remove the glaze along with a rering of pistons making much monies for the classis car garages and mechanics employed.

Byepass all that, deglaze your own bores by driving. It's not a "once off" process.

To be successfully bedded in the engine needs to be used at it's BMEP* area ( brake mean effective  pressure) which is where it develops the most pressure  throughout its power stroke (that's mostly found around the peak torque area) don't confuse this with revs !  Any "Ahaaa" thought here about "Italian tune ups" is exactly the opposite to what you should be doing.

In my 2.0 litre Ford S Max TDCI max torque and therefore max BMEP area is about the 1700 revs area, but to develop maximum  pressure which expands the piston rings and forces them into contact with the cylinder walls you need to be in top gear (6th) and be giving it full throttle, being in 4th or 5th gear on a part throttle don't cut the mustard. The long gradients on motorways are good for this, top gear at about 1400 revs give it full throttle until the revs get to 2000 then drop off the throttle and do it again, and again, and again. With the S Max it tows a 1700kg caravan about 2000 miles a year, that does an excellent job of re bedding in the rings. On race cars we do it on a rolling road and it can take 20 mins or more loading the cars engine with the revs on the rollers and applying maximum torque, or on cars which are MOT, taxed and tested about 200 miles on public roads. 
Don't confuse bedding in with wearing the engine out, without the rings gouging out the material from the cylinder bores the engine will not give the best mpg or power. If you think BMEP is mumbo jumbo google it.

Mick Richards

[astontr6]

20 hours ago, Motorsport Mickey said:

Brake Mean Effective Pressure

In the combustion cycle the most pressure is achieved upon the downward stroke of the piston on the power downward stroke (no surprises there). This pressure forces gas behind the piston rings into the piston ring slots and forces the piston rings outwards and into the engine cylinder walls gouging (steady, we are talking microns here) complimentary grooves into the walls with grooves in the piston rings. These grooves on the walls hold oil allowing it to be suctioned out as the rings pass allowing lubrication to the cylinder surfaces complimented by the maximum compression to be developed in the cylinder on it's upward compression stroke. There is a careful balance between enough oil for lubrication and too much oil which prevents the full expansion of the rings and upon a thousand miles or so of being burnished by the the oil sodden rings promotes ...glazed bores.

If you peruse the websites of "trophy car" owners there you will find "woe is me" tales of glazed bores mysteriously happening and the much monies a full strip down to hone the bores to remove the glaze along with a rering of pistons making much monies for the classis car garages and mechanics employed.

Byepass all that, deglaze your own bores by driving. It's not a "once off" process.

To be successfully bedded in the engine needs to be used at it's BMEP* area ( brake mean effective  pressure) which is where it develops the most pressure  throughout its power stroke (that's mostly found around the peak torque area) don't confuse this with revs !  Any "Ahaaa" thought here about "Italian tune ups" is exactly the opposite to what you should be doing.

In my 2.0 litre Ford S Max TDCI max torque and therefore max BMEP area is about the 1700 revs area, but to develop maximum  pressure which expands the piston rings and forces them into contact with the cylinder walls you need to be in top gear (6th) and be giving it full throttle, being in 4th or 5th gear on a part throttle don't cut the mustard. The long gradients on motorways are good for this, top gear at about 1400 revs give it full throttle until the revs get to 2000 then drop off the throttle and do it again, and again, and again. With the S Max it tows a 1700kg caravan about 2000 miles a year, that does an excellent job of re bedding in the rings. On race cars we do it on a rolling road and it can take 20 mins or more loading the cars engine with the revs on the rollers and applying maximum torque, or on cars which are MOT, taxed and tested about 200 miles on public roads. 
Don't confuse bedding in with wearing the engine out, without the rings gouging out the material from the cylinder bores the engine will not give the best mpg or power. If you think BMEP is mumbo jumbo google it.

Mick Richards

Hi Mick!

Thanks very much for such a detailed response. My engine did suffer from glazed bores and I did at the time wonder how this occurred. In the end I fully rebuilt the engine and had it re-bored.

Bruce. 

[DRD]

On 2/18/2023 at 12:05 PM, roughground said:

Hi Al;l 

Thanks for the replies. The engine has SUs and has had the compression raised to 9.5:1. the ignition and fuel are correct but the compression is down. I did a check and found all cylinders to be 125psi. It doesn't burn oil and pulls well but not as good as my TR7, hence the questions. The engine has run about about 3000 miles of non aggressive driving since the rebuild.

It sounds as if the rebore is the least painful option, trouble is find someone in Lincoln to do it

Are all the pressures within 10% of each other?

Those compressions look like its a US spec head.

[roughground]

Many thanks for all the suggestions. The head is one of the last manufactured USA heads so had a very low compression ratio. The head was skimmed by 40 thou and the unleaded conversion done, new valve guides and valves.  I rechecked my measurements of the cylinder head and found small error in the numbers. It is probably less than 9.5:1 and near 9.0:1. I also checked  the lift on the Cam, 245 thou  +/- 2  on all, l reset the tappets and checked the timing.  So rather than strip down and pay for a minor improvement I'll live with it for the summer and next winter carry out some of the suggestions made!

[michaelfinnis]

An American spec TR6 has a marginally lower power output and higher weight than a TR7 (though more torque), so your TR7 may well feel a bit quicker.

[Kiwifrog]

On 3/9/2023 at 6:21 PM, roughground said:

Many thanks for all the suggestions. The head is one of the last manufactured USA heads so had a very low compression ratio. The head was skimmed by 40 thou and the unleaded conversion done, new valve guides and valves.  I rechecked my measurements of the cylinder head and found small error in the numbers. It is probably less than 9.5:1 and near 9.0:1. I also checked  the lift on the Cam, 245 thou  +/- 2  on all, l reset the tappets and checked the timing.  So rather than strip down and pay for a minor improvement I'll live with it for the summer and next winter carry out some of the suggestions made!

40 thou of an American head is not very much and will get it nowhere near the spec of a UK head, If I remember correctly I had  close to 220 thou removed from my very late  1976 TR6 US spec head. I will see if I can find the technical document that I used that gave all the specs and the heights and combustion  chamber specifications.

I also had to change the pushrods for the shorter Uk type

cheers

 

Alan

Edited March 11, 2023 by Kiwifrog
Technical