Removal and rebuilding of a Twincam

[rgh0]

Now finally into the assembly, which is the bit I like as its clean and interesting work compared to pulling an old engine apart


Lapped in the valves. The replacement QED race valve I got for the damaged No. 4 inlet was the same profile but unfortunately they have shortened the stem so too short for the head and springs I am using , also shorter than the common race valve length of 101 mm, why did they change it ?? I hunted through my spares and found a suitable used inlet, crack tested and checked it for stem wear and all was good so will reuse it. Inlet seats 1.0 mm wide and on the very edge of the 1.625 inch valve and the seats bored and porting to match. Exhaust seats 1.5 mm wide on the edge of the 1.4 inch valves and seats bored and porting to match.

New Tony Ingram light blue stripe race springs and other components ready for final clean and assembly. Decided not to reuse the existing or new QED red race springs as the Tony Ingram ones are nearly identical in install height and spring rates and are made of what appears to be a better steel grade so thought I would give them a try. They are also a bit cheaper with current exchange rates.

Valves and spring packs all fitted. I do hate fitting the split collets, sometimes it takes 30 seconds and other times it can take 10 minutes. Good thing there are only 8 valves!!. I get quicker as I go along as the adjustment of how much spring compression is needs is key, to much and the collet falls out , to little and you cant get it in, just right and it slips in, rotates to the bottom and stays while you fit the second one and release the compressor. New retainer to replace the damaged one from No.4 inlet Tony Ingram has changed the design of his titanium retainers slightly but he sent me one to his older design to match the other 7, nice service.

You will note the cleaned exhaust valves are still black on the face from the carbon adsorbed into the surface of the stainless steel. The inlet valves run cooler and dont stain the same.

The studs all go back into the head now. The brackets on the middle two inlets are for the dual throttle springs required by the race regulations here, they mount on extended carb studs.

Pulling the plugs out of the end of the cams and cleaning the oil passage in the cams, lots of metal in there from the bearing failure and filter by passing.

Cams mounted for trial shim fit , I use old bearings at this stage and non nyloc nuts as it may be coming on and off a couple of times, though if I got my measurements right, hopefully the first shims fit is spot on... HA Ha HA I wish !

Ran out of time so have to wait until next weekend to bolt it down and check the clearances.

cheers
Rohan

[rgh0]

Well I bolted the cams down and set the clearances on then bench and then after I had finished it all I noticed this !!

The crack was in the No1 cam cap which is the end of the cam next to No4 inlet which is where the follower sleeve was badly worn. My assumption is the loads due to the worn follower jamming in the sleeve at some time had cracked the cap. I took the photo at an angle and with lighting that made it very visible it did not stand out much when just working on the head and i was lucky I spotted it.

Getting a new cap and then line boring the cam tunnels to fit it was starting to look like a very expensive option. Luckily ( or unluckily) I have collected quite a few cam caps from heads that have been scrapped due to being to soft or breaking through into water passages to badly to be repaired when porting for racing over the years. I went through my collection and found about 6 out of 28 that aligned well horizontally and vertically, one of those was actually a No1 cap so I did not even have to renumber it !!

Horizontal alignment can be felt when the cap is fitted to the head as you can feel with your finger a step in the join with the head of about 0.01 mm. The required matching Vertical dimension of the cap I measured with a dial gauge to see if the free play of my head measuring tool machined to fit with 0.20 mm clearance in the new cap was the same as all the other caps

After doing the checks I assembled the cam back in the head and check the valve clearance which I had set previously and that had not changed. I also checked the bearing clearance using flexigauge which came out within tolerance. Finally I pulled the valves out and bolted down the cam to ensure it could be turned freely by hand and was not binding. All was OK


It is well worth trying this if you can if you have a problem with one cap on a head to avoid the cost of line boring. I expect some of the regular twin cam builders in UK and USA would have similar cap collections and it appears tolerances on the machining originally done are such that a reasonable proportion of caps are interchangeable.

cheers
Rohan

[vstibbard]

A very lucky pick up Rohan.

V

[lotusfan]

Hi Rohan

Thank you for posting such an interesting thread.

When you have set the valve clearances on the bench do you find that they change after you have bolted the head to the block? Just curious because I have found that they do change.

[rgh0]

Hi Mike
Yes i find some of them will probably close up a thou or two when I bolt the head to the block. How much a change you get probably relates to type of head gasket used, and bolt tension achieved and the free flatness of the head and block.

cheers
Rohan

[alan.barker]

Many thanks Rohan,
this is a very interresting subject.
Alan

[Andy Hamblin]

I'd be interested to know what kind of starter ring gear you are using with the pre-engage. Is it one with a lead in on both sides or did you just reverse the standard gear? From the photo yours looks a little unusual with teeth longer than normal and on a slight angle - could just be an optical illusion from the photo though.

Standard starter ring gear with lead in bevel both front and rear. The angle of the photo creates the impression of longer and angled teeth. I think. i have run the same Bosch prengage starter from 70's Fords on flywheels with no lead in on the engine side where the pinion comes in from without problems

cheers
Rohan

Rhoan, just picking up this part of your thread - I have just bought a WOSP pre-engaged starter motor, so the pinion will throw in from the front, rather than the back like the old Lucas unit it is replacing.

From the state of the pinion on the Lucas, I suspected the worst for the state of the ring gear but actually its not too bad so I might get away with not pulling the engine to replace the ring gear.

One thing though - the bevel on the ring gear is on the back, there is no bevel of the front leading edge. Now, if the WOSP throws the pinion in from the front I was wondering f this would work ok. From what you said it sounds like it might.

Thoughts appreciated.

[rgh0]

As I said I have had pre-engage starters work OK without a lead in on the side of the flywheel they enter from and just relying on the lead in angle on the pinion, so its worth a try. If you find a problem with them blocking and not engaging then you can always pull the engine to change the ring gear but with any luck you will not have to.

cheers
Rohan

[Hawksfield]

Hi Rohan lotusfan
I had a similar experience as lotusfan after QED had fitted new guides and seats and shimmed the head for me.
After installing the head I noticed the clearances were not correct I was disappointed with QED but later realised that movement does take place. This was quite a few years ago and QED has been fully vindicated in its quality of work. pity they do not carry out machining work today.

Excellent thread Rohan thanks

[2cams70]

How is repair of the crankshaft going? Brett and the guys at Crankshaft Rebuilders do excellent work.

[rgh0]

Unfortunately going slowly due to the 2nd Covid lockdown. Its been straightened and stress relieved hopefully was ground last week and then will need re-heat treatment. They are very busy as everyone is rebuilding their engines due to the cancellation of all racing !!

This weekend I will start final preparation of the rest of the bottom end for the re-assembly once I get the crank back. I need to pull all the oil gallery plugs and clean the passages and clean and check the oil pump and cooler for any residual debris

cheers
Rohan

[jk952]

Rohan,
Great post, like the pulley jacking idea, I may need to use that. I have a leaky engine that bugs me, I suspect front cover poor sealing, also may have sloppy valve guides re oil usage, though not overly smokey, will check this fall/winter as the great weather! - but not car active (nor otherwise) - summer winds down here in the great white north.

Did you keep your existing valve guides, and not machine touch seats or valve surfaces, or did I miss that part?
Jack

[rgh0]

Hi Jack


Guides and valve stems were all Ok and within clearance tolerances. I just replace the No 4 inlet valve as the top had been slightly damaged by the rocking follower and lapped in all the valves.

cheers
Rohan

[Frogelan]

@ Andy Hamblin

I have bought a similar starter (made by Edge supplied by Cambridgemotorsport parts). When I purchased this, CMSP (Jon) asked me to measure the position of the flywheel compared to the engine so that the starter motor pinion could be properly set up.

This seemed a very good idea to me and a useful way to avoid headaches later on.

Andrew

[rgh0]

Progress is slow with the current lock down in Melbourne stopping work on my crank regrinding...... hopefully in the next couple of weeks I can get the crank back.

The head work is all finished and ready to be bolted on so have now been preparing everything else to be ready when the crank comes back

block and oil passages cleaned

Pistons and rods being cleaned. I decided to use 4 new rods rather than just replace the one that overheated when the bearing spun and failed as the new rods were all perfectly matched and I would have had to do some balancing to match the new rod to the old remaining 3 rods weight. I will save that for a later engine build.

Ordered a new Quaife gear set and planning to build a new spare competition box for my Elan, as my current one needs a strip and check and seal and bearing replacements, after many years of reliable service. I will see if I get the parts and can complete the build on that new box by the time the engine is ready and before racing recommences I hope in early 2021.

cheers
Rohan