Spitfire Spitfire - Gearbox & Oil Pressure?

[dklawson]

This post has two questions. I'm sure these topics have been beaten to death over the years so please don't flam me for asking them again.

After weeks of tinkering I got enough of our project '72 Spitfire reassembled to take it around the block today. I think it's the first time in two years (and three owners) that the car has moved an appreciable distance on its own power. Today's brief around-the-block drive precipitated two questions.

1) Oil Pressure. What pressure trips the factory oil pressure switch? I don't know what oil the previous owner left in the block but below 800 RPM the oil pressure light comes on. I'll be fitting a gauge later but what would a target oil pressure be for a 1300 engine running 20W50, at 800 RPM, when the coolant is around 180oF?

2) I went through our GT6 gearbox many years ago "just because". The Spitfire may "need" this attention. I was getting grinding on upshifts from 1st to 2nd and 2nd to 3rd. This was with the pedal all the way down and shifting at low road speeds. Again, this was a once-around-the-block drive with a marginally roadworthy car. I wasn't reving the engine or pushing anything. I'll be reading Haynes and Bentley tonight, but I don't remember the GT6 having any clutch adjustments... am I looking at synchros (and/or a used gearbox) ? Might I be "lucky" that the slave isn't moving the throw out arm far enough?

 

[Andrew Mace]

Oil pressure switches are supposed to trip at something like 7 lbs/in. With a warmed-up 1300 engine at idle, I'd hope for at least 25-30 lbs/in pressure. Much less than that, and it might be time for new big-end bearings at the least.

AS for the shifting problems, realistically the Spitfire has no clutch adjustment. (Some will suggest filing a new slot in the slave cylinder and relocating it thusly, but that's a band-aid at best.) Assuming both cylinders are good, I'd bleed again and see if it improves. If not, I'd look to see if the pivot pin for the throwout bearing arm is falling/has fallen out. After THAT, I'd check crankshaft fore-and-aft play due to worn/dropped thrust washers.

 

[TR3driver]

No idea if this applies to a Spit or not, but on other Triumphs I've seen a lot of worn pins & holes where the clutch MC pushrod joins with the clutch pedal. The wear here really adds up and results in lost motion.

 

[skucera]

I've never seen the exact spec on the oil pressure sensor in a Spitfire, so this is conjecture. Fords have this light come on at 6 psi, and GM cars have it come on at 7.5 psi. If the Spitfire's sensor is similar, you've got a mighty worn engine with dangerously low oil pressure. There aren't any simple things to check that might easily correct an oil pressure loss, like the BMW big six cam oiler banjo which is right up on the top of the engine and simply loosens sometimes, so the only way to really know is to take the engine apart and see what is worn.

Your "grindage" on shifts may be created by simpler causes than you mention. You may simply need to bleed air out of the clutch hydraulics, or the clutch throw-out bearing may be worn, or the fingers on the pressure plate may be worn. But, yeah, it is possible that if these things are fine that your synchros are worn. Given the Oil light coming on, that is quite possible, but you'll want to look at the simpler, more customary causes first.

Scott

 

[TR3driver]

To test whether the clutch is dragging (as opposed to bad synchros), stop the car, hold the clutch fully depressed, shift into first (or any) gear then into neutral, wait a beat, then try reverse. If reverse grinds under these conditions, your clutch (or pilot bearing) is dragging.

 

[dklawson]

Randall, I'll try that next time I take the car around the block. However, I don't anticipate any issue with drag as the car seemed to do OK in 1st and 4th.

I don't know which issue upsets me more. I'll start with an oil change to fresh 20W50 and fit a calibrated oil pressure gauge to see if I really have an oil pressure problem or not. We checked the crank play (by crow bar) before buying the car so I don't anticipate that being a problem.

I rebuilt the GT6 gearbox years ago so I'm not intimidated by the thought of that. I'm simply irritated that in the space of less than a month so many unexpected expenses have surfaced. I know that you have to expect the unexpected with an LBC project... but REALLY !! This was not the best weekend.

 

[TR3driver]

Well, my point was that, if the clutch isn't dragging, there's no need to worry about adjusting it, bleeding, etc.

Would it make you feel better if I told my tale of woe with the Stag I bought just to have a Triumph to take to Triumphest? First the rear brakes, then the front brakes locked up before I even got it home! Starter died, now the replacement is flaky. And I just got word today that the new mainshaft for the gearbox's second rebuild is on backorder, so no TRfest again this year. In two years of ownership, I think I've actually driven it about 3 weeks ...

 

[eejay56]

It's not unusual for the oil pressure light to be flickering at idle when fully warm especially with old mystery oil. I'd recommend swapping the thermostat to the 165 degree one. It's not hard to pull the pan without removing the engine, then you could check the bearings with plastigage and eliminate doubt. I second checking the pin that holds the clutch release lever. I had issues with that. You should be able to check it with the tunnel out. Mine now has cotter pins top and bottom. I also had a clutch pedal wear through and break at the top where it connects to the MC

 

[Andrew Mace]

Doug, after reading subsequent posts of yours and others, I'd agree that the gearbox problem might be as simple as worn synchros. Both 2nd and 3rd are somewhat prone to that. But it wouldn't hurt to double-check the oil level in the gearbox and top up as needed.

 

[dklawson]

I will check the gearbox oil and the pins as soon as possible. I'll also bleed the clutch just in case that's part of the problem. As I work through this project less and less of the car's interior is installed so pulling the tunnel cover is not such a big deal.

Andy, you know Jamie Palmer. I've been calling on him for advice and if worse comes to worse, I may be buying a used gearbox from him. As I said, years ago I went through the GT6 gearbox and I'm not opposed to doing that again if I have to... I just don't want to. There are so many other things on this car that need attention.

Eric, the oil in this car may be old in months/years but it's not old from use. It's still golden, not the lovely black LBCs turn oil after a few days of driving. Still... I wouldn't put it past either of the past two owners to have filled the engine with 10W30 or some thin synthetic blend. I'll start with a 20W50 oil change and install a pressure gauge before contemplating what may need fixing (if anything).

 

[Andrew Mace]

...As I said, years ago I went through the GT6 gearbox and I'm not opposed to doing that again if I have to... I just don't want to. There are so many other things on this car that need attention.

Understood. Besides, last I knew, it was not easy to get GOOD quality synchros; in fact, many folks recommend trying to find good used ones!

... I wouldn't put it past either of the past two owners to have filled the engine with 10W30 or some thin synthetic blend. I'll start with a 20W50 oil change and install a pressure gauge before contemplating what may need fixing (if anything).

Wouldn't be at all surprised if a thin oil is the problem, or at least a good part of it.

 

[70herald]

Both 2nd and 3rd are somewhat prone to that. But it wouldn't hurt to double-check the oil level in the gearbox and top up as needed.

The second time I rebuilt my transmission, I used parts from multiple boxes and carefully comparing parts, I found that there was also a LARGE variation in the size/ angle of the cone side of the syncro. Obviously ST's quality control was not so great. With on of the 2nd gears I had, the syncro ring would have begun acting "worn out" almost immediately since the cone was just a bit to small.

I think that the problem with the currently available rings is that they are to soft. they work real well for the first few shifts but then wear out very quickly.

Doug, before you go swapping gearboxes try using a specific manual transmission fluid (try Amsoil / or Redline) the additive packages in these oils are designed to help the syncro in their job unlike general purpose gear oils which frequently have additive which are needed for limited slip diffs etc, but reduce the effectiveness of the syncro. My personal choice would be either Redline 75W90 NS or 75W140 NS given the local temperatures.

 

[dklawson]

My personal choice would be either Redline 75W90 NS or 75W140 NS given the local temperatures.

I was pricing synchros from the usual sources and they aren't that expensive to gamble on... IF I decide to open the gearbox up at all. When I went through the Mini's gearbox I got hold of "bad" syncrhos from the U.K. and wish I'd left well enough alone. I bought parts to do that gearbox "again" but haven't touched the car since I can drive it the way it is. The Spitfire would not be considered driveable in its current state. IF I buy synchros, I'll pay attention to the fit of the conical surfaces. Are there other components that routinely need replacing when the synchros have worn? Again, if Jamie can help me out with a good used box at a reasonable price that my be my best option for a quick fix.

Thanks for the suggestion on the gearbox oil. When you are suggesting your choice based on local temperatures, do you mean your local temperatures or mine?

 

[billspit]

Its been quite a while since I read this, but the synchros were said to be too tall. They needed to be dressed down a few thous. I've not heard they were too soft, but I'm sure that's possible. It would be great if you could find some old NOS ones on fleabay.

 

[70herald]

I had several different boxes which I used to find enough good parts to build a nice box. Parts that wear include the syncros, layshaft, and all the metal bearings and spacers. If the gears are damaged, the cost of rebuilding the box won't be reasonable.

Probably hotter here at least in the summer.

 

[dklawson]

I'm going to set aside my gearbox frustration until I know whether or not Jamie does have a 1500 gearbox for us. If he does, the cost of that gearbox will be less than buying a set of synchros, new layshaft, and bearings. I'll let you know what happens.

 

[tdskip]

Any update on the oil pressure?

(fingers are crossed for you)

 

[dklawson]

I'm married, but I do the cooking for our family and unfortunately there's no daylight after dinner. The oil pressure will have to wait until the weekend. I have a Smiths mechanical oil pressure gauge and I'm planning on checking its calibration one evening this week. Hopefully I'll install the gauge, change the oil, and check the real pressure this weekend.