Compression Test Results

[Chris1966]

Hi,

 

Trying to work out how bad my engine is before having work done on it this winter, I just got a BMIHT cert. that says it is original to the car so going to work with what I have got.

 

Car is 1962 TR4, standard engine specification.

 

I not exactly sure what to make of the difference between the dry and wet compression figures I took today.

 

The engine was rebuilt in 2001 by a TR Specialist and in the first few years was only driven a few hundred miles a year. Since buying the car last July I have driven 1400 miles.

 

The exhaust smokes slightly on the over-run, which is commonly held to be valve guide wear, and also uses about 1lt of oil per 150 miles with some leaking as usual. Oil pressure when above 2,000 revs 50-60 lbs , in summer with hot engine at 750 revs 20ish lbs (once or twice 15lbs) after oil change and idle set a bit too low so I turned the screws a bit as it goes to stall anyway to get 1,000 revs and 25ish lbs.

 

Dry

 

155

149

151

153

All within 4% = good

 

199

195

190

200

All within 5% = good, but 26 - 31% more than dry

 

 

So no obvious rogue cylinder problem yet all showing high increase, so are they all worn or never made a good seal from the rebuild, or is there something else going on?

 

I have read in other threads that not running an engine much after a rebuild does not help. Which makes me wonder what is going on, engine rebuild 16 years ago and only 3,500 miles driven. Although the dry figures look okay it is just a basic tester and you can only judge between your own reading so both sets could be higher than 'normal'.

 

I'm not thinking of having the same TR specialist rebuild it anyway, but it should not really be having problems yet should it?

 

Photos of plugs attached, they all looked okay to me?

 

 

Thanks

 

 

Chris

 

 

 

 

 

 

[RogerH]

Hi Chris ,

I'm no expert but -

1Ltr/150 miles is very very poor

Oilo pressure sounds good

The dry - wet values are uniform

However there is quite a difference between the two sets.

 

The wet test suggests the rings - so it looks like your rings have either worn early or simply haven't done enough miles to bed in. (Pray for the latter)

The bores may well be glazed.

Roger

Edited November 2, 2016 by RogerH

[Malcolm Tatton]

Chris, this thread may help in case it is glazed bores.

 

http://www.tr-register.co.uk/forums/index.php?/topic/54256-high-oil-use/?hl=bmep&do=findComment&comment=448378

 

 

[Stanpartmanpartwolf]

Oil control rings have been incorrectly fitted- the expander rail will probably have jumped over itself.

If you are lucky, it's an easy fix & may not require much other work; though, if you do find the rings are at fault, start to look for other quality issues.

PM for more gen if you like.

Cheers

SPMPW

[Motorsport Mickey]

+1 on the bores being glazed.

The engine hasn't been used in the correct rev range, it's hardly been used. If you've been "Driving Miss Daisey" ie trickling along in top overdrive at 50mph you can reckon that the engine ie piston rings and cylinder bores have not bedded in to each other. This glazes the bores because the piston rings aren't sealing correctly on the cylinder walls, they are just sliding over the walls and the oil stood there. Then good news is you stand a chance of fixing it for free as long as you drive it in a disciplined manner.
You need to fully expand the piston rings so that they penetrate the oil "force field" surface which covers the cylinder bores. No...you don't drive it like you stole it, top revs are not the answer, for the rings to expand to the fullest extent the engine needs BMEP* (Brake Mean Effective Pressure running) Google it. If you check many of the "trophy" car websites and forums you'll find the problem spread across many car marques (Porsches are a good example). The piston rings need bedding into the cylinder walls such as they "gouge" (steady, we are talking microns) the cylinder walls. If inspected minutely the cylinder walls will show grooves which match those on the piston rings, and even as the piston rings twist around (ha...you thought they were fixed ? and that's why they were fitted staggered !) but that's another subject covered here on the forum in another thread, they improve the compression, power, and oil scavenging affect of the piston rings. This avoids the cylinder bores becoming glazed with all their attendant problems.
So the diagnosis is glazed bores and the cure is BMEP running, how to do it ?
BMEP running is achieved when the engine is driven under max load at the correct revs for the piston rings to be squeezed out the maximum amount and bedded into the bores. The BMEP occurs upon the downward power stroke normally when the engine is around the point of maximum torque, so the treatment is to run the car under load in top gear at those revs. So motorway gradients are good for this, top gear about 800 revs below the point of max torque and floor the throttle and keep it there, when the car accelerates up to the point of max torque, release the throttle and brake the car down to the same 800 revs below max torque in top gear and floor the throttle, again and again. I would expect to do this 2 or 3 times weekly for maybe 6 weeks before any worthwhile improvement is noted. Then continue driving the car in a suitable manner to avoid the glazed bore curse occurring again, my normal driver ( a Ford S Max diesel) benefits from towing a 1700 kg caravan about 3000 mile a year which keeps it nicely tuned to good performance and economy.

 

Mick Richards

Edited November 1, 2016 by Motorsport Mickey

[Chris1966]

Thanks for the replies.

 

Malcolm / Mike I had seen Mike's post from before which got me thinking it could be the low mileage and possibly the driving style of the previous owner that has not helped things. I don't think my style of driving has added to the problem although I don't think it has got much better over the year either.

 

Thanks

 

Chris

[Peter Cobbold]

What about using a running in oil and then driving at 3500rpm at WOT ? Will that help break the glaze?

eg http://www.classic-oils.net/Penrite-Running-In-Oil

Peter

Edited November 1, 2016 by Peter Cobbold

[PhilipB]

This looks like it's made for the job

 

Millers Liquid Glaze Bust

 

http://www.classic-oils.net/Millers-Liquid-Glaze-Blast

 

Anyone used ot?

 

Phil

[boxofbits]

Hi Chris

 

When an 'engine rebuild' is mentioned, people often assume that everything has been overhauled, ie new pistons, crank regrind, new shells, valves and guides, cam etc, but that might not be the case at all.

 

Unless you have the original receipt and specification of work carried out, there is no way of telling what level of rebuild was carried out. If the pistons seemed in good order at the time, they may have just been deglazed and put back in. The crank may have just had new bearings without a re-grind, and maybe a new cam, followers and chain. It may not have been subject to a full rebuild and it doesn't sound like the valve guides were replaced. Could have just had a budget refresh.

 

As Roger pointed out there is a real difference between wet and dry readings on all four pots and 1 litre of oil per 150 miles is abysmal. That's only around 900 miles per sump full! I'd start with new valve guides to perhaps get rid of over run smoking, iron out any leaks if you can, check valve seats are unleaded and see if that improves things first.

 

Regards

 

Kevin

[Prospect]

+1 for Oil control rings incorrectly fitted. I had very similar issue after an engine rebuild. Using oil at the ate of 100 miles to a pint of oil. Tried everything through to from deglazing as suggested to putting in a closed circuit engine breather without success. In the end stripped the engine again only to discover oil control rings on 1 and 3 pots incorrectly fitted as suggested above. Engine now spot on and oil usage about 750 miles to a pint almost worryingly low!

Deglazing worth a go but if does not work suggest go checking the rings before spending a lot of time and money as I did.

Good luck

Tony

[Chris1966]

Hi,

 

Thanks for the information on glaze, budget rebuild, bodge with oil rings

 

I'm starting to think budget rebuild / bodge are going to be more likely than glaze. I had a good look through the old invoices for work on the car and can find:

 

Polish crank and chemical clean

new camshaft

Unleaded inserts

 

But no mention of new liners and pistons as part of the 'engine rebuild', although the total invoice amount is not exactly budget, and no clue as to when they may have been done before in the invoices.

 

Best regards

 

Chris

[Motorsport Mickey]

I'm starting to think budget rebuild / bodge are going to be more likely than glaze. I had a good look through the old invoices for work on the car and can find:

 

 

If the car has only had the crank out and cleaned and polished then I'd suspect the rebuilders has not even replaced the rings or honed it, why would they ? more time and money when they could lift the owners leg by just doing the bottom end.

 

PS: I didn't know the Poles sold cranks for these ?

 

Mick Richards

[Lebro]

[RogerH]

OMG - if the Polish are doing cranks what chance have I with my project.

 

Roger

[Alec Pringle]

No Problem, Roger . . . . . don't worry about the Poles, focus on the Barge . . . . .

 

Cheers

 

Alec