Twin cam Valve Guides.

[rgh0]

If they are smart they would use close to original journal size then if you have a problem or wear you can get it taken out a bit and fit lotus shells.

The integral cam bearing journals in the new heads are identical to the old heads with bearing shells in place so you can use the same cams. Thus re line boring to the orginal heads size enables fitting of the bearing shells if you need to in the future.

cheers
Rohan

[rgh0]

The twink was originally designed for the cams running in the aluminum. Aluminum has much greater load carrying capacity than lead/tin babbit bearing shells. Today's machine tools also provide much better adherence to the original clearance and line bore tolerances.

The cams were always designed to run in bearing shells as far as i am aware. The first prototype engines had 4 bearings per cam. The fifth half size bearing was added at the rear after problems with failures at the unsupported rear end of the cam. The cam buckets originally ran straight in the aluminium but reverted to cast iron sleeve liners after wear problems.

Your right that modern macnine tools make creation of unlined bearings easier than in the past but you still had to create a true line bore and good surfaces to fit a set of bearing shells for the cams

cheers
Rohan

[Grizzly]

Bit of an update on my engine......

well it runs and sounds fine but i have oil coming out of the water pump (the water pump-rad pipe) and as i fitted a new pump i think i must have damaged the rubber seal replacing the front cover..... GUTTED...... So i'm going to sulk for a day then pull it to bits again and see where the oil is coming from......

[Grizzly]

Bit happier now, After every thing cooled down i noticed the oil residue had set (went really thick) and it occurred to me that i used a fair amount of Vaseline too lube the seals when i assembled it, so i think/hope its just that melting and running out. Geez that have me a scare...

[Grizzly]

Well whilst the engine was out (well it was in the rolling chassis) i decided it was a good idea to give the bottom end the once over (was going to do it with the head work but didn't want too play with to much incase it went wrong for any reason), so i've stripped it and measured every thing up / Replaced the Shells and rings the bore was in good order but the top ring was quite worn which was odd, so i have given the bore a good hone which i left well in tolerance for the std rings and fitted genuine Lotus rings. So now i'm happy the bottom and top end are sound.

So i completed the bottom end yesterday and have just fitted it back into the chassis and got it running.... to my horror have smoke again when you fit new rings do they smoke when bedding in? I'm not panicking too much just yet as my compression is now 160psi which is at the bottom of the range so i think there is some bedding to be done. I just hate the Blue smoke....

[elansprint71]

I'll let those more expert than myself comment on your smoke.

One alarming thing I've had after a re-build is mayo on the oil filler cap. Obviously one fears that the head/gasket is duff; however it seems that quite a bit of condensation can build up (even in "summer"). A chap told me that he had experienced this after a VW Beetle engine re-build, which was very reassuring at the time.

[Grizzly]

Tbh i think Mayo in the Oil cap is quite common (its mayo on the dipstick you don't want), i have had a few cars that mess the caps up i believe its the moisture that condenses from the air, i was told its a sign the oil filler cap seal or cam cover gasket is goosed.

I'm just starting to think i should have left mine when it was not smoking........

Out of interest did you rebuild your bottom end? did you get any smoke when it first started? i admit it is better after 10 mins of running but the temps where creaping up so i left it too cool down and find a bigger fan for infront of the rad...

[elansprint71]

Tbh i think Mayo in the Oil cap is quite common (its mayo on the dipstick you don't want), i have had a few cars that mess the caps up i believe its the moisture that condenses from the air, i was told its a sign the oil filler cap seal or cam cover gasket is goosed.

I'm just starting to think i should have left mine when it was not smoking........

Out of interest did you rebuild your bottom end? did you get any smoke when it first started? i admit it is better after 10 mins of running but the temps where creaping up so i left it too cool down and find a bigger fan for infront of the rad...

I did not rebuild the bottom end, having convinced myself that the loose guide was the culprit. This seems to have been a good decision, after a belch of smoke on first start up and a small amount the next day, it does not appear to smoke at all now.

I neglected to re-torque the head after a week and the head gasket leaked enough to pressurise the cooling system and blow some of the water out, no clues from the temperature gauge that anything was amiss but fortunately I only did short trips and made frequent checks, so no harm done.

[Grizzly]

Thats sounds just like my engine did when i refitted the head after the guides... I can't believe i thought it would be a good idea to change the rings etc after it was smoke free if it doesn't clear up i'm going to be kicking my self for weeks...

Classic case of don't fix whats not broken

[rgh0]

smoking in a newly partially rebuilt engine is not uncommon

could be rings not seated - the orginal style cast iron single piece Lotus oil rings are hard to get to seat properly. How round and worn were the bores and pistons versus the original grading tolerances. Was the honing done to a true professional standard or did you just roughen up the bore at little?

could be valve guide clearances to big - have they been reamed to the correct tolerances.

could be head flooding with to much oil - how worn were your cam bearings - did you replace them?

could be running in not completed adequatley - I do 50 full load acceleration cycles from 3000 to 5000 rpm and then coast down and then repeat - after this the rings should be properly seated

no easy fix if the smoke remains unacceptable after the running in is competed

cheers
Rohan

[Grizzly]

smoking in a newly partially rebuilt engine is not uncommon

could be rings not seated - the orginal style cast iron single piece Lotus oil rings are hard to get to seat properly. How round and worn were the bores and pistons versus the original grading tolerances. Was the honing done to a true professional standard or did you just roughen up the bore at little?Rohan

I spent quite along time measuring the bores top to bottom and for round, apart from a slight lip and minimal wear at the top and bottom (i guess its where the con rod drags the piston ) they where in good condition to the factory standard measurements (well within tolerance), i don't build engines very often but the hone appeared to be fine (was round etc after finished and when i wound the engine over pre head and engine oil i got the right noise from the bore/pistons)

could be valve guide clearances to big - have they been reamed to the correct tolerances.

If anything they may be too tight, i had a selection of reamers i drilled and reamed a block of brass then measured each valve and tried it in the block to make 100% and used the appropriate reamer to valve/Guide.

could be head flooding with to much oil - how worn were your cam bearings - did you replace them?

Thats Interesting, i didn't change my cam bearings as they looked in good order. But that said there is allot of oil collecting in the cam boxes? so maybe worth a go?

could be running in not completed adequatley - I do 50 full load acceleration cycles from 3000 to 5000 rpm and then coast down and then repeat - after this the rings should be properly seated

Unfortunately i don't have the use of a Dyno, its just rigged up in the chassis with two big fans in front of the rad. So i can't put load on it.

no easy fix if the smoke remains unacceptable after the running in is competed.

I seem to have done a full circle, gone from smokey engine to non smokey engine and now managed to make it smoke again I may run it a bit more and see if it goes a bit if thats the case i'll fit it and use it in the car to run in, if not i'm go into a dark room and cry......

[rgh0]

I do the run in on the road. put it in 3rd gear full throttle accelerate 3000 to 5000 coast back to 3000 and repeat for about an hour and 50 cylcles - run in done after that. Does the run in quick and prevents glazing the bores which can happen if to gentle and dont run under load to get gas pressure on the rings

cheers
Rohan

[Grizzly]

Well i have run it for 20 mins or so and the smoke is dying back so i'll leave it now until its back together. I'll let you know how it goes when its drivable.

[SJ Lambert]

Are the Colisbro guides the ones to use? I see QED stock them, Burtons are described as bronze........

James

[rgh0]

Are the Colisbro guides the ones to use? I see QED stock them, Burtons are described as bronze........

James

I would use the Colsibro guides from QED as my first choice. Reaming them accurately as more of a challange as I believe they need a tungsten carbide or diamond reamer to be done accurately and to the right surface finish so find a good machine shop who has the right equipment to do it.

The more usual Aluminium Bronze guides work fine also but just dont last quite as long but that is not really an issue in most twin cams these days with there limited mileage. I understand reaming them is also easier to do with standard reamers.

regards
Rohan