Nasty findings in Twink today.

[kenny]

Thought I'd have a break from the electrics/trim etc. etc. and have a look at the engine that came with this +2 project....it was sold as " was rebuilt but haven't run it" which I believe..............anyway the nightmare started when I lifted cam cover

Any comments on the following would be more than appreciated thanks

1) Five of the cam carrier bolts on inlet side have been taken up a size, thay all clamp tight so not a worry but one was missing a guide sleeve so I thought I'll remove head and investigate ways of sorting........ideas welcomed

2) Then notices before I lift head that on TDC I can get the exhaust cam sprocket in line with top of head surface but inlet sprocket is about 30 degrees advanced ......again comments welcomed

It gets worse...............

3) Lifts head and finds a set of brand new +040" pistons (cams were also new/refurbed by the way) gleaming at me.Then I realise no.3 piston has damage...............the damage is quite heavy as though it's been battered with a blunt centre punch all around its crown the full 360 degrees, and about 6 or 7 milli in, just up to the small recess. There is rough centre punch type damage in no.3 chamber in head also........this is not detonation I don't think and I've found no foriegn body to blame............Just don't understand. Am I OK just to smooth the marks out with air grinder?

4) This one worried me the most really...................When no.1 and 4 piston are at TDC you can rattle them in the bore with your fingers about 20 thou at least..............no.2 &3 feel tight,
Rotate the motor bring up 2 & 3 and they wobble..................1 and 4 go Ok at bottom.

I've never noticed this before when fitting pistons.......is this normal on a twink?, are these a short skirted piston which give this effect?

It feels like they are +40's in a +90 rebore.................help please.

This project is now getting the better of me (although I've got the wiring done )

Any help, comments or thoughts appreciated.......sorry for the long post.

Thanks Kenny

[SimonH]

That doesnt sound too good.

1) The cam cap bolts must be due to someone stripping the threads in the past, why couldnt they have helicoiled them? Guess the only place to get a dowel for the cam cap will be a dealer or a scrap head.

2) Chain slipped? Or just shoddy rebuild. Not good whatever the reason.

3) Spark plug tip fallen off? Seen similar damage before though not on a twincam.

4) Shouldnt do that, maximum piston to bore clearance should be 0.003". Sounds like a rebore is needed. Seems strange if this had been rebuilt?

[gordonlund]

Kenny,

Don't mess about. Sounds like a cowboy has been here. Strip the engine completely and find out what other mischief he has been up to. If you are not to happy with what you find you will have to take the bull by the horns and commit to a total rebuild or run the risk of a major blowup. Conrods through the side of a twincam are not a pretty sight. Find a good engine recon man who you can trust. Lotus specialists abound up & down the country, some better than others some more expensive than others. You pays your money and takes your choice. If you are confident in doing it yourself then all the better. A good twin cam should be nice and tight with clearances just sufficeint to enable the engine to be turned by hand with the spark plugs removed.

[rgh0]

Kenny
It sounds like a pretty poor rebuild.

With the cam caps - if the missing aligment dowel can be replaced and then the cam turned freely by hand with a new set of cam bearings then your probably OK. Though why they did not just helicoil the stripped studs is a question I would try to understand as it may be hiding other problems

With the valve timing - I am surprised the valves were not hitting the pistons with the inlet timing 30 degrees out, have a careful look at the inlet valves as they may be bent. This can occur very easily if the engine builder does not know what they were doing.


With the damage in No3 cylinder - I have seen similar damage in twin cams from bits coming in the inlet or breaking of a spark plug tip or breaking a spark plug insulator and bits dropping down into the bore when the plug is rmoved. Again a sign of a poor rebuild. It sounds like the engine was run at some time or at least turned over on a starter for this type of damage to occur. Depending on how bad it is you may want to get the head welded up and I would replace the piston as you dont know what damage the impacts may have done to it

With the piston movement - some degree of movement is normal. While the bore clearance is 0.003 inch the pistons have a tapered shape and thus can rock in the bores a little when cold. The tops of the pistons run hotter than the bottom and the taper allows for the differential expansion.

You need to remove the pistons and measure them at the manufacturers specified point which is usually at gudgeon pin height and 90 degrees to the pin to be sure if the bore clearances are correct and compare this to the bore over its full length.


In general I would say pull the entire engine down and start from scratch verifiying all dimensions as you put it back together as you probably cannot trust anything that has been done on it.

regards
Rohan

[kenny]

Thanks for the input so far lads........appreciated.
Slept on it last night and have just been in garage to have another look.

I am taking the head in tomorrow to have cam cap bolts sorted.

I have had another look at the damage to n.3 piston and chamber and to be honest I think I can sort this with the air grinder. it's not as bad as I made myself believe yesterday when I was still shocked at the find.

Rohan, The chap I bought it off who did not buid this engine actually did start it up I've found out now. He says it sounded well with no trauma but it had a rattle/tappety noise which he put down to a shim..............I now believe this to be an object of some sort in chamber 3.

I put a quantity of thin Mobil 1 oil before retiring last night into a bore resting on a piston to see if it stays there or creeps past..........it's still there this morning.

Rohan, I'm more than keen to know and was very interested in your statement re. the piston wobble. As I say with any of the pistons at top of the bore I can rock them........not as bad as I stated yesterday but a rock of about 10 thou. Does this seem acceptable seeing the pistons are new and un-carboned

I sold all my measuring equipment a year or so back when I "finished with projects" so can't at present do comprehensive checks. Just seems impossible that bores are too big for new + 40 pistons...........I'd love to know if anyone has tried rocking a new piston at the top of a fresh bore.

Thanks again,

Kenny

[rgh0]

Kenny

I have rocked new pistons in new bores and they do rock. I have never measured the movement but it is visible and I would guess around 10 thou side to side. But you will not really know if the bore clearances are right unless you pull a piston and measure the piston and the bore.

The piston should only rock along the line parallel with the gudgeon pin, that is across the block. It should be much more stable at right angles to this.

You need to pull No3 piston out to check it for damage if your intending reusing it (which I would not recommend) so you can check the bore clearances then if you can borrow some measuring equipment.

regards
Rohan

[kenny]

Thanks for that Rohan, I've just gone out to garage to check what you say. It appears at TDC the piston will rock about 10 thou but in either plane.........ie acoss block and also inline..............I'll wait for garage to warm up a bit then pull no.3 piston. I'm waiting to get my lent out engine hoist back and will remove complete unit during the week.

As for the damage I will try to post it here but will probably fail again

Thank you once more,

Kenny

[Dave-M]

Hi Kenny,
I have a spare pair of +40 pistons used but with no wear they are Hepolite with cast no 21093.
I have just meaured the taper top to bottom at 90 degrees to the pin and it's 30 thou on the diameter so 10 - 15 thou of rock would be what you would expect
Regards
Dave

[kenny]

Dave.........to the rescue again! Just had a chap around to house who is a mechanic and has done a few twincams, I showed him the movement I've explained and he says it is perfectly normal especially on a new set up.

Thanks for confirming that for me......phewww!

I will take Rohans advice on replacing the piston with the slight damage though. Mine are type c small cut out items and I will check serial number later.

Got the electrics completly sorted Dave last week by the way.............just need that pesky little flasher for headlights to complete now when I can identify the part needed!

Thanks again for that, speak later,

Kenny

[Dave-M]

Kenny, I would think a hazard warning light flasher unit would be the one you needed. It's a two pin job and as long as it's only switching a relay it will be fine.
From memory it's about 36 watts and should be up to the job.
A mini one should be OK
Can post you one if you cant find one but any factors should have one.
Regards
Dave

[rgh0]

Kenny

I would be a little worried still about the piston rock being the same in all directions. It should be restrained more in pivot along the length of the block as the piston cannot pivot around the gudgeon pin or crank in that axis - unless the gudgeon pin or big end clearances are excessive.

I have never measurd the difference but it is normally less in the length of the block direction with correct bearing clearances.

Rohan

[kenny]

You are right rohan re movement less in one plane. I've miced the bores and all is well although I have now lifted block for a good strip check and rebuild.

Re. the head I've taken it to Billy Bannister racing engines where he is re machining the cam cap studs out of billet and re inserting into head.

At the same time new guides have been suggested and will be fitted along with bringing the shims back up from .060" to circa .120".

He was checking head last night and we will decide action to be taken today. ie new seats/or valve stem adjustment.

It has also been suggested to fit the QED valve springs as I'm told they have infinite strength but coupled with thinner gauge wire.

I was wondering if these are the Isky (spelling suspect) springs which I've heard of people fitting to eliminate any worries of becoming coil bound?


Many thanks,

Kenny

[rgh0]

Kenny

If your down to doing the valve guides and the valves are sunk into the seats to give 60 thou shims then I would replace the seats also at the same time as doing the stems rather than fit special short stem valves

Most of the spcialist Lotus suppliers ( QED, Dave Bean The Elan Factory) can offer special high lift springs intended for use with high lift cam rather than standard Lotus cam lift. Not sure if ISKY have an offering for Twinks but other cam suppliers such as Kent do. These springs typically have thinner wire allowing a smaller fully compressed height and also typically have a lower spring rate allowing achievement of correct spring seat and cam nose spring loads with the typically longer valve stems used in conjunction with high lift cams. You normally dont need special springs or have any coil bind problems if using a stadard Lotus cam lift and have the valve shims in the standard range

Before you use a special spring you need to get the full spring specs such as supplied by Dave Bean in his catalogue and analyse the application in your particualr head.

Its not a trivial exercise setting up a non standard set of valve dimensions and spring pack to get all the variables right so they work properly together with a none standard cam. A good racing engine builder should know what he is doing and be able to give you the right setup for your particular head and any mods from the standard setup being proposed.

In my competition engines I normally aim for a seat spring load around 75 to 80lb and cam nose cam load around 200 lb max with an absolute max upper limit of 220 lb. If your building a competition engine you can also use shims under the springs to keep them all in the same load range and compensate for variation in spring pocket depth and valve seating height.

regards
Rohan

[kenny]

Hi Rohan, just got back from machine shop. I've opted for the cost effective route. Seats and guides to be replaced, General clean up on head with minimum skim. New cam bolt inserts.
In other words just enough to take the head back to manufacturers parameters.
For a road car I feel this is the sensible option. I know how my budgets went widly out of control when trying to eek the extra power from my previous Vauxhall and K series motors..................not this time, I'm older and wiser and don't compete anymore

Kenny