johnsimister
Active Member
The engine has done 66,000 miles. Before I took it to bits it blew no blue smoke and used practically no oil. But performance was very sluggish, especially on hills, despite all being correct in the ignition and carburation departments. Compressions varied between 152 and 160psi, some way off the 190psi this 10:1 compression engine should have.
I'm currently refurbishing the head: new valves (slight pitting on some seating faces beyond fixing by simply grinding-in the valves), and new guides (exhaust ones very worn). That should improve compression a bit. Getting the valve timing right should improve it quite a bit more; it was about 8 degrees retarded, which I have learned could reduce compression pressure by as much as 25psi. I'll be replacing the timing chains and tensioners – there was a chain rattle at idle, and the timing discrepancy suggests the chains might be worn – and also the main and big-end shells although oil pressure was good.
So, the bores. There's a wear ridge near the top of all of them, slight but undeniable. Given the foregoing re compression pressures, lack of smoke and oil usage etc, is it viable to leave the pistons and bores alone and still expect performance to be as it should be once the engine is back together? Or do I go the whole way, extract the engine, get it rebored and spend a worrying amount on new pistons? Obviously I would rather do the former, but not if the engine ends up still underperforming.
If a rebore is the only way ahead, is it OK to bore a 2000 block out to take 2200 pistons? I see the 2200 pistons don't have cut-outs for the valves – do they work OK with the flat-face 2000 TC head? Will I end up with the usual 2200 9:1 compression ratio (probably a good thing with today's fuels), or does a 2200 head have shallow combustion chambers so the valves don't protrude as far into the cylinder?
All advice gratefully received.
Thanks, John
I'm currently refurbishing the head: new valves (slight pitting on some seating faces beyond fixing by simply grinding-in the valves), and new guides (exhaust ones very worn). That should improve compression a bit. Getting the valve timing right should improve it quite a bit more; it was about 8 degrees retarded, which I have learned could reduce compression pressure by as much as 25psi. I'll be replacing the timing chains and tensioners – there was a chain rattle at idle, and the timing discrepancy suggests the chains might be worn – and also the main and big-end shells although oil pressure was good.
So, the bores. There's a wear ridge near the top of all of them, slight but undeniable. Given the foregoing re compression pressures, lack of smoke and oil usage etc, is it viable to leave the pistons and bores alone and still expect performance to be as it should be once the engine is back together? Or do I go the whole way, extract the engine, get it rebored and spend a worrying amount on new pistons? Obviously I would rather do the former, but not if the engine ends up still underperforming.
If a rebore is the only way ahead, is it OK to bore a 2000 block out to take 2200 pistons? I see the 2200 pistons don't have cut-outs for the valves – do they work OK with the flat-face 2000 TC head? Will I end up with the usual 2200 9:1 compression ratio (probably a good thing with today's fuels), or does a 2200 head have shallow combustion chambers so the valves don't protrude as far into the cylinder?
All advice gratefully received.
Thanks, John