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Spitfire 1296cc engine work


KM

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We have a 1296cc engine that requires some work prior to RBRR. Its consuming oil - about a litre every 200 miles. Have had the valve guides done and it no longer has blue smoke out of the exhaust. Its not coming out of the side of the engine either, the chassis is very dry. Have been advised the rings are the next step so the question is how difficult is it to do this job? (other suggestions for losing oil very welcome) Head off, sump off. Remove half conrod, slide out piston, remove old rings, size new rings in cylinder and file to size, fit rings and then put back together. My concern is that I don't have the tools to measure tolerances, apart from feeler gauge, and may do all the above only to find out more work is required. Any advice would be most welcome or alternatively suggestions for someone trustworthy who could do the work. I live in Lincolnshire.

Kevin

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Hi, before you go any further you must do a compression check on the four cylinders. This is simple but needs a gauge that connects to the sparkplug holes to measure the pressure produced in each combustion chamber as the engine is turned using its starter motor.

When you have them put the results on here and we can help decide the next step..... 

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Sorry, but it's essential to get some accurate measurements. This really means removing pistons to measure the bores.I doubt if low compression will cause that amount of oil use. More than likely it's getting past the rings due to worn cylinders. 

Sorry again, but with that sort of oil consumption she probably needs a rebore and all that goes with it.

Hope I'm wrong for yous sake. 🙁

Tony.

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Thanks for the advice. If its more than just rings then that is what it is. No compression test results yet because the prop is off to service the UJs so the exhaust is off too. Hopefully all back together over w/e.

Kevin

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Compression test doesn't need the exhaust on, except possibly to warm the engine up first - you are only going to spin the engine on the starter with all the plugs out........

Has been my experience that engines that are very heavy oil users (I've had a few!) can still give excellent compression results, possibly because the oil control was so bad every test was effectively a "wet" test!  Therefore not necessarily definitive.

It is possible to do a "ghetto" re-ring as you describe with the engine still in the car.  Colin is quite right about the honing though - this really is essential.  You can get suitable hones for this for use with electric drill (Flex-hone amongst others).  The biggest challenge is cleaning up afterwards as a certain amount of swarf and stray abrasive is produced that you really don't want in the engine.

While Tony is strictly correct about the need to measure everything properly, if the wear lip at the top of the bore is small and reasonably even all the way round and there is no gross damage elsewhere (scoring, scratching, rust-pitting) then it's reasonable to think that a hone and re-ring will produce an improvement.  It may take longer to bed in properly if the bores are a bit oval (they often are) and won't last as long as a proper rebore, but also much cheaper and easier.

As regards other suggestions re the oil use:

- Check breather system clear and working - does the engine breath much through it?

- Oil level correct.  If the wrong dipstick is fitted causing the engine to be over-filled, consumption may be rapid until the excess has been burned off.  What point are you topping up at?  If you are constantly topping up to the full mark it may be worth letting it go a bit further and seeing if it stabilises?

- Use the right oil.  Needs to be a decent 20/50.  I have found both Wynns oil treatment and STP to be quite effective at reducing oil use.  Kept my Vitesse engine alive and usable for an additional 5 years / 25K!

- At a litre every 200 miles I'd be expecting visible smoke.  That's really quite alot.....

Nick

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Took the breather pipe of the PV Valve to check oil wasn't being sucked through and went for a long drive down the Fosse Way. About 750cc oil used but also noticed drops of oil under front of engine which were not there previously. By the time we got home (180 miles) oil was pissing out the front. Difficult to tell exactly where but it looked like it was coming out between the block and the sump. Despite all the oil being added the oil coming out and on the dipstick was black. It looked like it was years old. To me this says the oil is being burnt and blown into the crank case. The speed the oil is leaking from the front also indicates significant crank case pressure. In addition oil is dropping out of the hole in the rocker cover cap. The engine is coming out tomorrow.

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  • 3 weeks later...

Kevin,

Check that the threads in the alloy stretcher block are not stripped, this can result in the oil escaping. Some companies are selling mild steel replacements, however you may be able to source a secondhand block. When re-fitting, do ensure that you fit the correct length studs. Be careful, dry build etc. Good luck

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Quoted from KM-

Compression numbers are:

158

154

154

152

Engine was hot.

Hi, good news: these readings look ok to me. 10psi higher would have been nice but theyre not bad and more importantly they are balanced so I cant see that 'blow by' of gasses can be a significant problem. Therefore Im not convinced you have an over pressurisation problem because I cant think of any other way this could be produced. Maybe you can confirm this by feeling for pressure from the PV connection pipe on the rocker box with the engine running? If not it sounds like the oil usage is purely down to leaks......

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