Iain T Posted July 1 Report Share Posted July 1 (edited) Adjusting my valve clearances today and noticed the rocker arm movement goes from the same height as the centre of the rocker shaft when closed to obviously lower when open. I have had the head skimmed around 1mm and had fitted a completely new rocker assembly. I had to fit shims under the pedestals to enable flitting possibly caused by the slightly higher lift cam with perhaps a larger effective diameter. It also causes the adjuster screws to touch the rocker cover 😡. The valve lift is as near as damn it 10mm. The pushrods measured inaccurately with a piece of welding wire are 8 inches or 203mm long. It seems the best way to solve the incorrect rocker arc and rocker tapping is to fit shorter pushrods and possibly remove the shims? Iain Edited July 1 by Iain T Link to comment Share on other sites More sharing options...
JohnD Posted July 1 Report Share Posted July 1 Iain, See the Revington's Information Sheet: https://www.revingtontr.com/information-sheets/is0066-rocker-geometry Link to comment Share on other sites More sharing options...
Iain T Posted July 1 Author Report Share Posted July 1 Thinking of how shorter the pushrods need to be if the rocker ratio is 1:1.5 and I need to lower by 6mm (5mm for half the valve stroke and 1mm shim) if the pushrod is shortened by 4mm it would be around about right. I could easily shorten another 3mm as the adjuster has a lot of travel. Iain Link to comment Share on other sites More sharing options...
Iain T Posted July 1 Author Report Share Posted July 1 (edited) 11 minutes ago, JohnD said: See the Revington's Information Sheet: John, I've read that and I do indeed need shorter pushrods. I'll speak to Revingtons tomorrow. Edited July 1 by Iain T Link to comment Share on other sites More sharing options...
Iain T Posted July 2 Author Report Share Posted July 2 Ideally to get the correct geometry I need to lower the pedestal by about 5mm by taking the shim out and machining 4mm off the pedestals. That seems a bit extreme and I don't know what that would do to the rocker to valve stem top contact swipe. More thinking and geometry calcs are required. Iain Link to comment Share on other sites More sharing options...
Iain T Posted July 2 Author Report Share Posted July 2 Revingtons don't have any pushrods less than 8". I'll try my engine builder tomorrow. Link to comment Share on other sites More sharing options...
JohnD Posted July 2 Report Share Posted July 2 Teeth of the gods! Lower the rocker shaft by 9mm? That's a third of an inch. How much did you skim the head? Suggest check your measurements!_ John Link to comment Share on other sites More sharing options...
Iain T Posted July 2 Author Report Share Posted July 2 (edited) 17 minutes ago, JohnD said: Lower the rocker shaft by 9mm? No 5mm, 4mm machined off the pedestal and removed the 1mm shim. I'm going to check it properly tomorrow as today I've been refitting the bonnet hinges links and adjusting. A combination of valve stem length, cam, followers and 1mm head skim has resulted in the odd arm geometry. Edited July 2 by Iain T Link to comment Share on other sites More sharing options...
Iain T Posted July 3 Author Report Share Posted July 3 I can't find a custom pushrod supplier in the UK so I've emailed by Manton and Trend in the USA, a country where they actually make parts and love the combustion engine! Iain Link to comment Share on other sites More sharing options...
JohnD Posted July 3 Report Share Posted July 3 Iain, Revington's WILL make your pushrods to your bespoke length! I know, I have some! JOhn Link to comment Share on other sites More sharing options...
Iain T Posted July 3 Author Report Share Posted July 3 (edited) John, I spoke to Mr Revington and he said he didn't offer a custom length supply. Perhaps it's too much hassle? When did they supply your push rods? Iain Edited July 3 by Iain T Link to comment Share on other sites More sharing options...
JohnD Posted July 3 Report Share Posted July 3 Iain, In April this year. I think you or he must have misunderstood the question, unless he has changed policy since then. See: PUSH ROD TR5/6 CP PI 8.11" (revingtontr.com) And the line "RTR1194 is 240mm long (overall length) but can be cut to length to suit individual engine requirements." John Link to comment Share on other sites More sharing options...
Iain T Posted July 3 Author Report Share Posted July 3 We did have a long conversation about various sizes and I mentioned I really need around 195mm but he never offered the RTR1194. However at £40 each that's two to three times the price of custom made in the USA which I bet is where Revingtons buy from! I'll let you know if I get a response from over the pond. Iain Link to comment Share on other sites More sharing options...
JohnD Posted July 3 Report Share Posted July 3 Beg to differ! Neil was away at the time, and I negotiated with Karl, who made them in a very short time. John Link to comment Share on other sites More sharing options...
Iain T Posted July 3 Author Report Share Posted July 3 I'll give Revingtons another ring tomorrow. It only takes 5 days to get rods from the US. Cheers Link to comment Share on other sites More sharing options...
Iain T Posted July 4 Author Report Share Posted July 4 15 hours ago, JohnD said: Beg to differ! Neil was away at the time, and I negotiated with Karl, who made them in a very short time. Just spoken to Neil and he said he can no longer supply the cut to size and doesn't know where to buy them from. You must have bought the last of his stock. The hunt goes on! Iain Link to comment Share on other sites More sharing options...
JohnD Posted July 4 Report Share Posted July 4 Thank you, Iain! Neil is busy 'rationalising' his business in anticipation of retirement, so maybe that is a part of the service he has cut out. Can't be that many customers, so, lucky me! John Link to comment Share on other sites More sharing options...
Iain T Posted July 4 Author Report Share Posted July 4 (edited) A result Racetorations can get them and at a reasonable price. I haven't had email responses from the three US manufacturers, Manton, Trend and BFE Edited July 4 by Iain T 1 Link to comment Share on other sites More sharing options...
Iain T Posted July 4 Author Report Share Posted July 4 22 hours ago, JohnD said: Karl, who made them in a very short time. John what length rods do you have? I have calculated I need 8mm shorter rods ie 195mm. I measured the heights of the shaft centre and valve stem and they are within 1mm so with 10mm of valve stroke I do infact need to lower the pedestals by 5mm Link to comment Share on other sites More sharing options...
Iain T Posted July 5 Author Report Share Posted July 5 More research and I'm leaning towards getting a narrow but centred rocker tip to valve stem swipe as more important than getting the shaft centre at the valve mid lift. It really all depends on the rocker design. There is no point getting the geometry 'correct' if the tip swipe is off centre or not swiping symmetrically about the centre as the valve moved up and down as this promotes valve guide wear. I'm going to do another swipe test. Iain Link to comment Share on other sites More sharing options...
Iain T Posted July 25 Author Report Share Posted July 25 (edited) Update, I did a swipe test and it's in the valve stem centre so on Monday I'm going to cut 2-3mm off the top of the adjuster screws and cut another slot for the screwdriver. Hopefully no more rocker cover tapping! Iain Edited July 25 by Iain T Link to comment Share on other sites More sharing options...
Iain T Posted July 30 Author Report Share Posted July 30 A result! I took 3mm off the length of the screw adjuster and recut the screwdriver slot. Out for a test drive tonight and zips up to 5000rpm without the accompanying rocker cover tambourine rattle😁 While the rockers where off I also backed off and retorqued each head nut. It's much quieter! Iain 1 Link to comment Share on other sites More sharing options...
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