hi all.
I bought a used camshaft with both holders on ebay that are in great shape and usable.
The engine is now fully disassembled, both top and bottom ends.
Top end:
INTAKE AND Exhaust valve guides need replacement.
I suggest using APE guides. You will need to have a machine shop install them and bore to proper clearances, which are TIGHT in this engine, and must be, or else it WILL burn oil afterward. Intake valve stems' clearance 0.0008"-0.0012", exhaust 0.0010-0.0018 (both are considered 'worn out' at 0.0024"). Then new valve seats must be cut to match the angle of the new guides. Yours might need exhaust valves: during valve refacing this will become apparent. New valves need not be refaced.
Valves and valve springs are within spec.
Cylinder bores are to spec and no rust or pitting.
If you do not elect to rebore with new pistons, I suggest getting Honda's own rings. The oil rings are thinner than most of them found today, and the standard rings sets will not fit the grooves - too thick/tall.
Have yet to measure the ring end gaps. Haven't bothered as I am looking at new rings.
Pistons are within spec. However there are small indentations, looks like the exhaust valves have been hitting the pistons.
Chances are the exhaust valves are then bent.
Cam chain tensioner rubber bits (rollers and guide) have seen better days. Still look usable but I will replace with new.
Cam chain is DID 219T and judging by the amount of adjustment left on the cam chain tensioner it is likely OK to reuse.
Bottom end.
There are many signs that the cases were split once before.
Had a hard time removing the bearing holder and striped the 4 screws. Dremel and impact driver to the rescue.
All gears look great.
Have yet to measure clearances on the connecting rods bearings and crankshaft bearings. There is no up and down play on the connecting rods, only some side play.
Bearing clearance (Plastigage) should be less than 0.0024", or else the oil pressure will be very low when the engine is at temperature.
Spec clearance is 0.0008"-0.0012" new.
There is some visible wear on the cases where the transmission and sprocket bearings sit.
All of the ball bearings are NTN with the exception of main-shaft bearing on the left side that is KOYO.
There is no play at all and no noise on the bearings when spun by hand. When I place any of the shafts on the cases and spin by hand then I can hear the usual ball bearing noise.
Primary chain is marked RK. I measured 67.5mm from case to tensioner, That is slightly above the mid range of the Honda specs 64mm-70mm.
Primary chain tensioner rubber is still soft yet the edge of the rubber have some wear. Planning to replace it.
advice needed.
Top end:
1) Recommendations of a reputable shop to replace all valve guides, without having to throw away usable parts for new sets of valves and springs.
2) Recommended piston rings (standard). Prices vary from 40$ per one piston to a whole lot less for all 4.
3) Is valve hitting pistons due to excessive wear on the exhaust valve guides? Once the head it rebuilt I will check the piston/valve clearances using molding clay. If still an issue, then a thicker head gasket from CycleX is the solution?
I NEVER recommend thicker head gaskets for these engines, period. Thicker head gaskets WILL cause major oil leakage problems, specifically at the 2 rear oil passages where the head and cylinder meet. In addition, to use any standard head gasket made today, you must either mill the deck of the clinders by 0.010" to use the standard 2.4mm thick O-rings there, or else get a pair of 2.6mm thick ones from me (for a donation of any amount to SOHC4.com) or - both - which is how I rebuild these engines.
There is no normal situation in this engine where the exhaust valves can even hit the pistons, unless they were rust-seized from sitting a long time, and then the engine was started up. This scenario is, sadly, common with the F2/3 and K7/8 bikes because of the cast-iron valve guides: they wear quickly and rust easily when the oil is old and wet and the bike is parked a long time.
4) Any better chains then DID 219T cam chain (stock?) and reasonably priced?
Bottom End.
5) How do you inspect transmission roller bearings? I know the advice is to replace with new. But looks like that someone before me already went through the trouble and expense, unless NTN with an one random Koyo were stock factory bearings.
6) Keep or replace the RK primary chain at half its lifespan?
Honda's 'distance' spec for primary chain wear on the K7/8 and F0/3 engines was...umm...optimistic. They were in midrange (i.e., about where yours are now) when the engines were first assembled. The gearing is such that they will typically last 80k miles or more if they do not have rust in them.
Attached are a couple of photos to show the wear marks on the case where the bearings sit. Should there be wear marks in these locations? Are the outer races of bearing meant to spin? Similar wear is noted on the outer race of the bearings.
Thank you all.
