TVR Griffith Replacing the Exhaust Gaskets
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My car is a 1996 Griffith 500 so some aspects of this article may not apply to your particular car, especially the Pre-Cat models.
I noticed a characteristic quite loud "Ticking" from the engine that seemed to clear when the engine was up to temperature. Close examination with a stethoscope traced an exhaust leak to the off side rear of the engine. Judging by other owners comments this is a very common problem. The replacement of the gaskets is without doubt the most awkward job I have done on the car during 13 years ownership. If you are wondering whether to tackle this at home it is essential that you have a four or two post lift or a pit as without adequate and easy access to the underside the job is virtually impossible. Even with a decent lift it is still a lengthy procedure. If your hands are rather large or if you have any doubts give it to your TVR dealer to fix you will not regret doing so.
First, the four top bolts on each manifold should be undone, if the heater rails are removed before hand on the off side it will give better access but with patience the UNC bolts can be removed without doing this. Ensure that you use a 9/16" AF spanner, I have seen recommendations elsewhere to use a 14mm spanner but this is a recipe for disaster as bolt heads can easily be rounded, you then have a real problem. The Rover V8 uses AF bolts unlike the rest of the car which is predominantly Metric. Underneath the car several items need to be removed to gain adequate access. The starter motor is fixed by two 5/16" Allen headed bolts and these can be extremely tight as the steel corrodes into the aluminium engine casting. The 100 amp fuse and holder is next, secured by two small metric bolts to the chassis. This then clears space on the off side. The pic shows the starter supported to save stressing the cables. Removing the exhaust system will give access to the near side. By placing a broom handle or similar on the ramp underneath the tail pipes will give some support when the exhaust is dropped and prevents straining the front junction until it is separated.
My car is a 1996 Griffith 500 so some aspects of this article may not apply to your particular car, especially the Pre-Cat models.
I noticed a characteristic quite loud "Ticking" from the engine that seemed to clear when the engine was up to temperature. Close examination with a stethoscope traced an exhaust leak to the off side rear of the engine. Judging by other owners comments this is a very common problem. The replacement of the gaskets is without doubt the most awkward job I have done on the car during 13 years ownership. If you are wondering whether to tackle this at home it is essential that you have a four or two post lift or a pit as without adequate and easy access to the underside the job is virtually impossible. Even with a decent lift it is still a lengthy procedure. If your hands are rather large or if you have any doubts give it to your TVR dealer to fix you will not regret doing so.
First, the four top bolts on each manifold should be undone, if the heater rails are removed before hand on the off side it will give better access but with patience the UNC bolts can be removed without doing this. Ensure that you use a 9/16" AF spanner, I have seen recommendations elsewhere to use a 14mm spanner but this is a recipe for disaster as bolt heads can easily be rounded, you then have a real problem. The Rover V8 uses AF bolts unlike the rest of the car which is predominantly Metric. Underneath the car several items need to be removed to gain adequate access. The starter motor is fixed by two 5/16" Allen headed bolts and these can be extremely tight as the steel corrodes into the aluminium engine casting. The 100 amp fuse and holder is next, secured by two small metric bolts to the chassis. This then clears space on the off side. The pic shows the starter supported to save stressing the cables. Removing the exhaust system will give access to the near side. By placing a broom handle or similar on the ramp underneath the tail pipes will give some support when the exhaust is dropped and prevents straining the front junction until it is separated.
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Now the difficult bit, removing the eight lower manifold bolts. Several bolts will only move a flat at a time so be patient. Eventually all of the bolts except those for cylinders 3 and 4 may be removed. The manifold has to be moved away from the head before these two bolts can be removed due to the tight bend of the manifold at these points. The manifolds can now be separated from the Y piece by removing the two tensioned bands. Be careful not to drop the manifolds or Y piece as the internal catalytic converters can easily be damaged. Old gasket sealer will no doubt be seen at the Y piece junctions and the bands and requires removing. Ensure the bands illustrated above right are completely free of gasket cement:
A word of warning before assembly, be very careful that all bolts into the aluminium head and block are not cross threaded so start them initially by hand before using a spanner to tighten. I obtained a new set of UNC steel bolts and spring washers from my local TVR dealer for a few pounds so false economy to reuse the old. Many owners have replaced the steel bolts with stainless studs and or bolts. A metallurgist friend strongly advises against this as there is a danger of them shearing. Stainless is apparently quite happy at low temperatures 0 to -50C but much less happy at high temperatures especially when subjected to hot/cold cycles. My local TVR garage always use steel bolts. Before reassembly I tried a bolt in every manifold head thread to check that they were free and one was cross threaded, not uncommon in aluminium heads. With care I re-threaded it with a UNC 16 tpi 3/8" tap. A 3/8" 16 tpi Whitworth tap is virtually identical so this can be used if the UNC tap is unavailable. The new gaskets were then stuck to the manifolds with contact glue to aid reassembly, this glue would burn off quickly in service. See pic:
A word of warning before assembly, be very careful that all bolts into the aluminium head and block are not cross threaded so start them initially by hand before using a spanner to tighten. I obtained a new set of UNC steel bolts and spring washers from my local TVR dealer for a few pounds so false economy to reuse the old. Many owners have replaced the steel bolts with stainless studs and or bolts. A metallurgist friend strongly advises against this as there is a danger of them shearing. Stainless is apparently quite happy at low temperatures 0 to -50C but much less happy at high temperatures especially when subjected to hot/cold cycles. My local TVR garage always use steel bolts. Before reassembly I tried a bolt in every manifold head thread to check that they were free and one was cross threaded, not uncommon in aluminium heads. With care I re-threaded it with a UNC 16 tpi 3/8" tap. A 3/8" 16 tpi Whitworth tap is virtually identical so this can be used if the UNC tap is unavailable. The new gaskets were then stuck to the manifolds with contact glue to aid reassembly, this glue would burn off quickly in service. See pic:
A 8.5mm drill was then passed through each manifold bolt hole to ensure that the gasket was not fouling and that the bolts would pass freely, this will be appreciated when reassembly begins. Position both manifolds carefully in place and replace all upper manifold bolts but do not tighten in fact only engage a few threads, these screw in relatively easily, copper ease on the threads will help later removal. Then tackle the lower bolts. Better to have a cup of tea at this point as the next stage is going to be frustrating. The two awkward bolts at cylinders 3 and 4 must be placed in the manifold first due to the tight bend and screwed a few threads into the head. As the engine mounts are close this is a pig of a job and some owners have removed the mounts for better access. I found it was just possible to get the threads started with patience. Looking at the pic:
If pressure is exerted on the bolt head by a piece of wood or screwdriver levered against the chassis rail while simultaneously tightening with a spanner, then with patience the bolt will enter. Only screw each bolt in a few threads. Replace all of the other lower bolts, also just for a few threads. Now having spread exhaust sealer on the Y junction it is time to carefully offer it up to mate with the manifolds. Unless the joints are coincident there is no point in trying to clamp them, the pics below show misaligned (left) and correctly aligned joints (right):
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This is the reason that the manifold bolts were loosely assembled so as to allow a bit of movement to align both manifolds with the Y piece. When aligned correctly the clamps can be tightened and then the manifold bolts into the head finally screwed home. 15lb feet is the recommended torque so go carefully with the spanner to avoid stripping the threads.
While the 100Amp fuse is accessible it is a good idea to change it as they are a constant source of trouble, my local TVR specialist changes it as a matter of course at each annual service. When I removed the fuse it fell apart in my hands, as shown so would have failed very soon. As a final check just tighten each manifold bolt as the gaskets could have compressed slightly thus loosening the bolts a little The starter motor can now be re installed being careful not to cross thread the Allen headed bolts. And the exhaust system re attached which is a fairly simple operation. Best of luck! |
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