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Mason Jones Member 
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I’m about to replace the timing belt (among other things) on the spare 74 engine before dropping it in. I was about to mark the old belt and pulleys but the cam pulleys don’t line up like the diagram in the manual. I turned the crank several times and made sure it was at TDC. The cam pulleys always line up like this when the timing mark on the crank pulley is lined up and #1 TDC:  Here’s where the timing mark is:  The diagram shows the “IN” mark on the intake cam pulley lining up with the “EX” mark on the exhaust cam pulley which is definitely not what I’m getting. I was told this engine ran well before the PO bought it. I’ll mark the old belt and pulleys before removing it. The belt looks very old, maybe it jumped a tooth (or several)? Last edited on 02-19-2012 08:11 pm by Mason Jones |
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Brett Gibson JH5 20497 Member
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Mason, if it was me I would remove the spark plug from #1 cyl. bring the crank up to the timing mark making sure that the #1 piston is at the top, (that way you know the crank pulley is in the right spot), mark the position of the distributor pulley, then remove the belt and line up both cams to the 110 mark, install the new belt. I would change the tensioner bearing at this time as well and when you tension the belt have the tension on the up side of the bearing, if you notice you can have the bearing tension in either direction. Brett |
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Mason Jones Member
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Dang, I was hoping that with careful marking of the pulleys I would avoid having to learn anything about cam timing! If you can’t tell, I know zip about cams. But I did check that the #1 piston was at the top when the crank’s timing mark was lined up. (*edit: removed dumb question that I answered by opening my eyes a bit.) The history of this engine is a big unknown, I've never seen it run. Can you tell what the cams are set to now from the photo? I mean what sort of performance would you get with what looks to be the inlet cam about 2 notches late and the exhaust cam about 2 notches early? Thanks for the help! Last edited on 02-21-2012 05:52 am by Mason Jones |
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Mason Jones Member
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Oh, duh, now I see the 110 & 115 on the pulleys (my wife's been telling me I need to start wearing glasses, I think she's right). Still curious why the cam timing was set the way it was. Last edited on 02-21-2012 04:55 am by Mason Jones |
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Brett Gibson JH5 20497 Member
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Mason, who knows why people do things or as you suggest maybe the timing slipped if that was the case before installing the engine I would try to check the compression on each cylinder first, you dont want to have to take it out again, but at least set the cam timing correctly first. Good luck Brett. |
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Mason Jones Member
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I plan to do the head gasket since I have it so I'll see if their is damage when I get the head off. (Also have the tensioner bearings you mentioned.) Keeping my fingers crossed... Thanks, Mason |
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Mason Jones Member
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Couldn’t wait for the weekend to get a look at the valves. Took the head off and looks like bad news. I think at least 2 of the valves are bent. Tested them with a spring compressor and one of the #3 exhaust valves is stuck. One of the #4’s moves but not smoothly. So I’m thinking now to save time and money I may just take the head off the working engine that’s in the car. The valves are noisy and need adjustment but it works. Any technical reason not to do that (other than the shame of being a lazy penny-pincher)? In this scenario the head would be off an early engine and the block would be the later version with improved oiling. Assuming all the holes line up... |
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Mason Jones Member
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Just for fun here’s the inside, good grief, running a little rich? The photos don't do justice to the amount of black crap in there:  |
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Tim Murphy Member 
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I notice that one of the cam pulleys has the Lotus name showing, the other does not. IIRC, both pulleys should be the same. If you reversed one pulley, does it change the timing marks? |
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Jensen Healey Super Moderator 
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Hi Tim, if you look at the intake and exhaust markings you will see that one pulley needs to be flipped. In 110 and ex 110 are not on the same side of the pulley. Kurt |
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Mason Jones Member
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I guess if nothing else I've learned that 2 notches off is enough to crunch some valves on the exhaust side. Intake valves all move smoothly. Unless someone tells me I shouldn't I'll probably pull the head off the old engine and transplant it to this one. Adjust the valves and see what happens. |
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MikeIsotech Member 
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This was discussed on the UK Jensen Owner's Club forum recently: http://www.joc.org.uk/phpBB2/viewtopic.php?f=5&t=12316 It looks like you can. Hope the link helps! Mike |
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Mason Jones Member
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Mike, Thanks for the link, very helpful! Nice to know what you're in for before getting everything apart. Reading other posts here I see that there was a later intake manifold for the Strombergs that had larger ports. Of the 3 manifolds I have lying around 1 is that later design so I'll use that one. I'm not sure how to tell if the pulleys on the 74 engine are the later aluminum alloy that is tougher. They seem a little less shiny than the 73's pulleys but could just be dirtier. The 73s are shiny and smooth whereas the 74s are very rough, even bumpy. Mason |
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pbahr Member 
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The diameter of the carbs should match the manifold. Not larger. Not smaller. YELODOG |
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Mason Jones Member
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I didn't measure the carb side of the manifold. I measured the engine side of the manifold and the later one has the bigger openings. That manifold was from the 74 JH engine. I guess I should measure the ports on the earlier 73 head and see if they match the manifold? Bigger holes on the manifold would be useless if the holes on the head are smaller, right? Once again, thanks for the info! |
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pbahr Member
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The hole diameter/size should ALWAYS match. Otherwise you get non-laminar flow which really screws up the flow to the engine. YELODOG |
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Mason Jones Member
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That's the trouble with options, requires more thinking. So, my options are: 1) Use the 74 head which appears to have larger ports which might give some improvement in performance. But I'll need to replace a few valves/guides. I would send it out but the budget for this is $0 so it will be a learning experience for me. 2) Use the 73 head (including it's matched manifold) and "just" adjust the valves and put it on the 74 block. Any clue how much of a gain in performance I might get from the later head? I saw the reference to the difference in this post: http://www.jensenhealey.com/forums/view_topic.php?id=172&forum_id=2 Mason |
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Jensen Healey Super Moderator
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If the budget is near $0 then your course is clear. When I was 16 years old we used to "rebuild" an engine by lapping the valves, honing the cylinder walls and throwing in some new rings and bearings, then wonder why the lump still smoked. If you have stock cams the difference in the intake size isn't going to make a noticeable change to the power output. Bigger isn't always better. The higher velocity air inside the smaller intake may be atomizing the fuel more efficiently. For the 8.5:1 compression and Stromberg carb engine it works just fine. If Lotus knew what they were doing would the stock Dellortos have been so poorly jetted they had that 2000 rpm flat spot? |
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Mason Jones Member
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Jensen Healey wrote: If the budget is near $0 then your course is clear. When I was 16 years old we used to "rebuild" an engine by lapping the valves, honing the cylinder walls and throwing in some new rings and bearings, then wonder why the lump still smoked. Haha, that's great! Unfortunately, while my wife is back in school my budget is about like it was when I was 16. For now I'll go with option 2--least opportunity for me to make things worse. |
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