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MG TD TF 1500 - XPAG rebuild oil use

I have just completed installing my rebuilt XPAG engine in my YT, but it is continually burning oil. The higher the revs the worse the smoke. Engine has run a maximum of only 2 hours. Originally thought it was just a running in problem, but ....

I rebuilt the engine in my mechanics workshop, under his supervision. I used new County pistons and new Grant Rings (purchased from MG Octagon Car Club). When fitting the rings, we had to get them filed down so they had the correct end gap (.008 <-> .010"), which we were not too happy doing, as we thought rings should be correct size. Block line bored etc, new rear speedi sleeve fitted. I am using Penrite Run in oil.

There is no oil in the coolant nor vice versa.
Pistons are 0.040 over size. Cylinder compression is (1-4): 167, 167, 165 & 160. (Test done using starter motor and no plugs in situ) Oil pressure at 1000 is 50psi and at 3000 60psi. Breather hose from Rocker Cover to air filter not attached.

Spark plugs when removed showed #1 semi clean with some oil, #2 very oiled up and probably not firing, #3 & #4 had burnt oil/fuel coating.
Draining the sump only produced 3 litres, 5+ litres was put in prior to start up.

Cylinder head removed today and cylinders show: #1 had some oil, #2 had a small pool of oil on piston, #3 & #4 had burnt a oil/fuel coating. Valves checked and I found the company that shimmed the cylinder head and fitted the larger valves has only used the outer spring on each valve. (Why didn't I pick this up earlier (when I unwrapped and installed the head) - now to chase the company up and see if they still have the inner springs)

My mechanic thinks the oil rings are not working properly and need to be replaced. Has anyone had problems with Grant rings? Or can anyone suggest another reason for the oil in cylinders and the excessive oil use.

TIA Stuart
Stuart Duncan

"Pool of oil on top of piston" sounds more like oil running down valve guides than ring failure. Now the head is off, pour kerosene on top of the valve spring retainers (with head tilted slightly to make retainer washers horizontal). Does the oil disappear and run down the valve stem or does it stay put? Perhaps he also left out the neoprene seals?
Also, the shrouds fit inside the inner springs, so they must be missing too!

I would check out these head issues first before any dismantling of the bottom end.

Good luck.
Bob
R L Schapel

A helpful tip when fitting original "O" ring seals.
Cut the tip off a caulk gun cone slightly higher than 8mm,chamfer the inside. Compress the valve springs,put the ring on the cone and put the cone on valve tip, push into place with a ring spanner that will push over the taper. Make sure the "O" ring fits in the collet groove before retaining with the collets.
Also make sure the shop did not lose the shrouds as well, most important with the old type seals
Ray TF 2884
Ray Lee

As Bob notes above, if you are missing the inner springs, the shrouds are probably gone as well. I use new 120# springs from County, and have been impressed with the consistency of their tension. I would not bother to shim springs, as you are just temporizing with weak springs, that will only get weaker. With excellent new springs available, why re-use?

I don't personally use Grant rings (I prefer Deves rings), but know that some rings have needed a good thousand miles before they were seated to the point where the engine no longer smoked. I would suggest - assuming guide leakage, seals and springs have been done - that you should run it more.

As for ring gaps, probably half my (Hastings, Grant, County, etc.) rings used to need some sort of small adjustment, before I switched to Deves. They fit perfectly.

Are you using a break-in procedure? Proper break-in makes a big difference with ring seating.

Tom Lange
MGT Repair
t lange

My TF was using so much oil after an engine rebuild that my wife made me push it to the end of the drive before starting it. The house was reeking of burnt oil fumes. Using Bob's test i.e. seeing if oil leaked away from the valve collet retainer rings I realised the problem was the guides. I had fitted the "O" rings to the valve stems rather than in the collet retainers. I bit the bullet, pressed out the guides, turned grooves in them and fitted Mini seals and the problem is totally cured.

Jan T
J Targosz

I have valve spring shims in stock, .015", .030" & .060", to achieve the proper installed spring height. I also have in stock Positive Stop Teflon valve stem seals.
Len Fanelli


Len Fanelli

I believe that at the GOTF in Orlando last year, Glen of Glens MG Garage St Petersberg mentioned engines smoking after a complete rebuild and the problem was the pistons. Something about the oil groves not having enough return holes to allow the oil scrapped off the bore to return to the sump. They solved this by having the pistons machined to increase the number of holes in the skirt. I don't remember who's new pistons were in use, possibly Moss.

The only other thought would be the O ring missing under the collets.
Rod Jones

One other thing is if the valve guide shroud was fitted upside down - You would pool oil on the guide top and get a lot of oil - Even if the O rings were there and fitted correctly. I don't know if with the inner springs missing it would allow the shroud to fall down? I don't think so. But have never seen that.


Rod Jones

Thank you guys for your suggestions.
My first thought was the O rings were missing, but we compressed a couple of the valve springs and found the O Rings correctly positioned under the collets, but I do not remember seeing any oil deflectors. (probably not installed as no inner springs were installed.

I am away for a week, some 730km from home, visiting our daughter and the grand kids.

When I get home I will again check the springs for oil deflectors, and do what Bob suggested to see if oil is seeping past the valve guides, plus chase up what happened to the inner springs and oil deflectors.

Tom, todate the car has not been driven except in and out of shed, but I have run engine for 20min at 2000 to 2500rpms. Once I sort out the oil problem I will do some runs in the local area and put 800km on the engine. I will be trying to keep high revs, varying the rev range, do some hard acceleration and do some driving up the nearby hills.

Again thanks for your feedback.
Stuart
Stuart Duncan

Len,

Please can you explain what your spring shims do and how the correct thickness is determined also, do the teflon seals require machining a larger recess in the valve stem?

(sorry to hijack this thread, but curiosity got the better of me)


John

J Scragg

John - when springs get a bit used up, they lose some of their tension, and no longer provide positive valve closing. Machine shops have a tester that measures pressure at a pre-determined spring height, to see if a spring is in spec. I have been known, when in a hurry, to use a bathroom scale on a drill press to do the same thing.

One way to boost the spring pressure is by putting a shim on the head under the spring, to shorten the spring and therefore increase the pressure.

My feeling is that such a procedure is a throwback to the old days when engines were rebuilt as inexpensively as possible; now that good springs are available, it makes sense to replace them. The old springs are only going to get weaker, after all, and valve float will set it at lower and lower RPMs...

Tom Lange
MGT Repair
t lange

Stuart - I'm not at all convinced that you have a problem! Running at 2500 RPM will break in the cam and lifters, but will do nothing to seat the rings. The engine needs to be under load for that.

My method sounds like yours: I run in the cool of the evening, and warn the police that I will be driving through town all night. I try not to lug, try to drive up and down gentle hills, and watch the temperature like a hawk. The main thing I do is accelerate and decelerate hard - the former forces the rings against the cylinder wall, the latter sucks up oil from the sump to lubricate and cool.

I run the car up to 2500-3000, and then smartly lift my foot off until it is down to 1,000, and do that for an hour or so. I gradually increase the RPMs, constantly accelerating and decelerating - steady RPMs are not good. At the end of the night I change oil and filter, and do that procedure twice more.

It often takes a thousand miles before an engine's rings are fully seated; more than one engine I have built has come back due to smoking, and all I do is drive it for a few days to break it in, and then return it, to universal satisfaction - and no smoke!

Other than the spring problem I doubt you will find anything else wrong.

Tom Lange
MGT Repair

t lange

For proper valve spring seat pressure, installed height of outer springs needs to be 1.847". On the bench all springs, new or used, should be the same height.Due to manufacturing tolerances, replacement parts QC, of valves springs, valve spring retainers & cotters, as well as distance from the valve seat to the cylinder head machined surface for the lower spring locator, Valves and seats resurfacing, cotter & retainer wear stacking up these dimensions will change the installed spring height.Shims are located under the lower spring locator, it is common engine building practice, but perhaps not so much for engines designed now.
My Teflon Positive Stop valve stem seals do require the top of the guide to be machined to .419"-.429" outer diameter & .250" down from the top of the guide.
Of course Tom is correct about " Machine shops have spring pressure testers" to verify spring pressures @ recommended installed spring height.
Shims are .015", .030" & .060" thick.
Hope this helps.
Len
Len Fanelli

Tom,

Thanks for your reply, I would never dream of trying to reuse old tired springs, they are easily available and not expensive. If a garage did this job for a customer it is easy to imagine that labour costs may exceed the price of a new set of springs.

John
J Scragg

Len,

Thanks, OK that is much clearer now, One more question, what is the ill effect of not balancing the springs. I have a spare head (with all new parts) on the bench and can see that the upper spring holders are sitting at different heights, I thought this was tolerance spread and was negligible.

John
J Scragg

Sounds like you skipped step 1, COMPRESSION TEST.

Are you sure you have an banjo bolt on the line up to the head with a restricting orifice? You could be flooding the top of the head with oil.
JIM N

John I would take a good look at the valve cotter or keeper depth in the spring retainer, the cotters do wear, not sure if the retainer wears where the cotters seat. Also check if the valve heads are the same height from the head gasket surface to the valve head @ the combustion chamber ceiling.
Len Fanelli

Len,

All the parts on the head are new so we can exclude wear. I placed a straight edge on the top of all 8 valve stems and they are perfectly lined up. I then removed 2 spring retainers, the highest and the lowest, swapped them and rechecked the alignment. This changed, the lowest remained low and the highest remained high. this proves that the problem is in the diameter of the tapered hole in the keepers. The question is what would happen if I keep them that way?

John
J Scragg

Hi all
An update on my engine rebuild problems. Sorry about the length.

FYI, I have been told what I thought was oil smoke, was actually caused by an excessively rich fuel setting. Leaner carbi jets on order.

The cylinder head was worked on last year whilst I was overseas and then wrapped up and painted and I hadn't noticed when I put the engine together that the duel valve springs I provided were not used. Instead a single spring was installed on each valve. (Original and supplied springs have gone missing)

As I am using one of Len's camshafts and roller lifters, I thought I had better check the spring compression. Took the head back to the cylinder head rebuilder and found they were about 90#. After shimming they are now 130#, as he though the 165# recommended was too high for a road car, not expected to rev above 4500. As the engine has roller lifters, there is no need to bed in the lifters, so once together it will be out on the road being driven (as my mechanic says) "like it is stolen" (ie hard driving).

Put the head back on and started engine only to find water leaking up the thread of the centre stud on manifold side. Also found the stud to be loose. On removing the side cover, noticed water leaking out of the gasket at the front spur, which I think may be due to the loose stud. On removing the head and taking out the problem stud, inspection revealed a hole through the bottom of the hole into the water passage.

As the engine had been rebuilt when I bought the YT, I think whoever did it may have cut through into the water passage when chasing the stud hole thread. Today I coated the stud with Loctite thread sealer and screwed it back into a cleaned out block hole.

Hopefully, tomorrow the new head gasket arrives, which I will coat with copper spray before fitting. Engine should all be back together day after tomorrow, when I will give an update report.

Stuart
Stuart Duncan

From Engine Builder Magazine: "Milder solid roller cams can use 165 lbs. on the seat, but that is the minimum you should try to use".
Stuart it sounds like your engine builder has never before assembled an engine with a solid roller lifter / follower camshaft.
Len
Len Fanelli

Stuart contact me via email

Bill Chasser
TD-4834
W A Chasser

A bit later than I hoped to report back, but I am quite happy with how the engine now performs.

We found that when hot the engine would not idle, on examination it was found the choke was not backing all the way off, caused by having a braided chock cable, in lieu of a solid cable. Once the chock is pulled forward engine idles nicely. New chock cable to be purchased.

No leaks around the head.

Engine revs nicely, and gets to 4000rpm easily. Now to put some miles on the engine/car. Engine is so quiet compared to before the rebuild. No tappet chatter due to roller lifters and cam.

Having pulled the head twice, I can now get it off in a couple of hours.

cheers
Stuart

ps. this morning I visited a club member with 4 TCs, to check his latest TC purchase for concessional club rego. The TC has been shorted by 6" and a Marshall Supercharger fitted.
Stuart Duncan

So what did you find that was causing your oil above the pistons issue ?.

There were a few very handy hints offered, so it would be appreciated to know by all what you found.

Are you back to running twin valve springs ?.

Cheers

Tony
A L SLATTERY

To answer Tony's questions.
Oil on top of pistons is believed to be caused by ME putting too much oil in the sump (over 6 lts) and the rings not being bedded in. I miss read the manual. Now running with 5 lts, plus what is in the filter.

Still have single valve springs, like I believe a lot of other T & Y owners.

Engine running much too rich and we have leaned the carbs as much as possible. New needles and jets purchased and will be inserted after Easter.

Ran the car (YT) yesterday as requested by mechanic. In top and 3rd gear starting at 1000rpm accelerate hard to 4000-4500rpm a number of times. One time whilst in 3rd, I noticed rev counter indicating 5,500rpm -(I am going to have to watch my acceleration). Engine has been line bored and balanced and runs so smooth.

Thanks to all who offered suggestions.
cheers
Stuart
Stuart Duncan

This thread was discussed between 18/02/2019 and 12/04/2019

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