Engine Rebuild Part I - Head & Cylinder Rebuild

The Interceptor ran well before it was taken apart a couple of years ago but needed attention. The shocks and forks had no damping in them, the fuel tank was missing and the rear wheel bearings were falling out. On a positive note it started on the third kick when I put fuel in the lines and added a battery. It idled well and made no unusual  mechanical noises so I did not expect major problems when I took the engine apart.

Breaking things down and getting them ready to rebuild. 

The RE has a quirkiness about it that I rather like. Following up the Hornet restoration with the Interceptor offered many learning opportunities. For example the cylinders and heads on the Interceptor are four pieces and not two as on the other British bikes I am familiar with. The strength inherent to the one piece design is lacking in this one. RE owners have devised some unique methods to overcome this weakness. Connecting the heads by putting straps between the head bolts ties things together while beefing up the head to frame mount by bracing its halves together provides additional strength.

The RE split head and split cylinder design. 

Taking the head apart revealed no big surprises. The valve stems were worn slightly out of spec but the seats looked good. After dis-assembly the castings were soda blasted and washed up to remove blasting residue. The head was heated to 225 F and the valve guides were removed. The guide insert holes were measured with pin gauges finding three guides at nominal and one oversize. Replacement parts were ordered from sources in the UK.

The intake and exhaust ports were pretty smooth right from the factory with no excessive flash being found in the exhaust ports as on my BSA's. I left the exhaust alone and polished the intake to a 320 grit finish. I was careful not to remove much material and kept my focus on producing a nice swirl.

Taking the heads apart.....no surprises with the RE. 

The before and after picture. I prefer soda blasting as it does not alter the  finish as much as bead blasting does and leaves no grit to damage moving surfaces. 

The Interceptor has a dual spring per valve setup. 

Talk about attention to detail. "Enfield" stamped on the valve stem.

The new valves, ordered from Hitchock's, are very high quality and pieces of art to a mechanical nerd like myself . 

The tools used to recondition the head.

An adjustable hand reamer was used to remove  galling in the guide holes being careful not to increase their size. This facilitates alignment of the new guides to the seats. 

My custom guide installation tool patterned from workshop manual pics. I have used a drift but prefer the press. The heads were heated to 225 F and the guides were put in the freezer for a couple of hours before installing them. 

I have found that bronze guides usually need to be reamed and lapped after installation as the holes close up a bit when they are pressed in. 

The Interceptor intake valve seat profile. 

The Interceptor calls for an intake valve seat profile I have not worked with before. It is fully radiused with no flat and I would like to see the cutter for it. The manual warns of a "deleterious effect" if the contour is modified and recommends returning it to the factory for service although a special cutter is available. The manual notes that a 45 deg cutter can be used in emergency situations. The new valves were 45 deg and the seats dressed up well with minimal material removal using a 45 deg cutter. I don't think the minor change in profile will impact performance......emergency repair complete.   

The seats had slight pitting and only required a light dressing with the carbide cutter. This was followed up with lapping to remove cutter marks. 

Getting the final seal with grinding compound. Finished seats are a dull grey. I lap the seats until cutter marks are removed and no light will shine through from behind the valve.

My new and reconditioned part set. The valve adjusting screws had flats worn on them and were replaced with elephant foot adjusters - front center.

Not to be outdone by the head the RE cylinder also has a quirkiness about it with its head to cylinder sealing feature called a "cross ring". This is a conical shaped ring that fits into a cone machined in the cylinder. The cross ring replaces the copper or composite head gasket found on most machines. As the head is tightened down it presses the ring into the cylinder cone forcing a seal. Head bolt torque is quite low compared to other bikes. A note of importance is that boring a cylinder requires a larger cross ring to match the new bore. Failure to heed this will find piston interference with the ring which is not good. The original rings were split while the modern production is a one piece design.

The cylinder bored and honed with the +.020 cross ring sitting over the bore. Note the chamfer it fits in at the top of the cylinder. On the left are the push rod hole seals. An aluminum piece fits in the cylinder and a rubber piece fits into a recess on the bottom of the head. 

My Interceptor did not have an air filter which was an option for 1969. Was the air not as dusty in '69? I was quite young and don't remember. Anyway the bores were worn larger at the top by about .007/inch which was out of spec. They were also worn more on the sides than fore and aft which I found odd. They were taken to EV Engineering in Howard City Michigan to bore and hone them +.020 per the RE workshop manual and matched to the pistons which varied .001 in size from one another. The pistons were the machined variety and purchased from the UK with OEM rings to seal things up. I used this setup on my BSA Hornet and it is working well although I would use forged pistons for heavier applications.

The top end ready to put on the lower cases .......

On to the next.......

Not exactly motorcycle related  ......."Grandpa Ken" spent time in England during WWII in the US Army Air Corps working on B17's. He left us a few photos of  his group's planes and this is one of my favorites.