Rebuild advice

Started By: Richard LeBaron on 2014-01-26 09:44:37

I have a '76 XJ6C that spun a big end bearing on cylinder #1. I was hoping to just work that but one cylinder bore is out of spec by .0015 so I guess I need to bore the block to .020 over. Question: this has HS-8 carbs. Since I will need new pistons with an oversize bore, should I go to 9:1 compression? I still have a BW-65 automatic so does the extra power even matter? Should that slight out of spec cylinder be ignored to save $800?

thanks

Comments

Whre are you located/ If in a smog test state, check the rules. If yes, I would suggest finding an earlier engine in order to make life easier, otherwise you need to rebuild your engine completely.

Define out of spec please.

Do you mean vs original bore or vs maximum permitted wear?

Pete (your fellow NCJOC member)

Thanks for the response and yes those are the HS-8s I got from you. The spec describes 3 different piston possibilities so I took the minimum maximum bore as my measure. All were under that except cylinder 3 which was in spec along the block length and .0015 OOS across the block. No lip at the top of stroke so I thought I was all set. Compression was good before tear down on all cylinders. If I need to bore to an oversize due to this slight OOS should I go to 9:1 or is that overkill for BW65 AT? Also, not a smog state...

Hello Richard.
If your bore is only out by .0015 (15 ten thousandths), it seems like a ,020 (20 thousandths) may not be needed. I suppose it wouldn't hurt though.

The BW65 isn't the most rugged transmission but I'd think it could handle the extra power of a .020 overbore and 9:1 pistons and the HD8s. I'd estimate you'd gain about 20 bhp with those mods - so about 10%? Maybe I'm off on that but even with a 40hp gain, the bands in the tranny are getting an extra 15% torque or so after the converter.

I'd say go for it and build the engine the way you want it. If it blows the trans, you can always upgrade that without much fuss.

The car sounds fine. Remember that your 'tuned' state was normal for everywhere else. Enjoy the car as is and don't worry about 8:1 unless you want/find some good used standard 9:1 pistons to fit with new rings. I would be worried about why on earth it lost a bearing, where the debris is inside the crank and if the rod eye is still round.

The car sounds fine. Remember that your 'tuned' state was normal for everywhere else. Enjoy the car as is and don't worry about 8:1 unless you want/find some good used standard 9:1 pistons to fit with new rings. I would be worried about why on earth it lost a bearing, where the debris is inside the crank and if the rod eye is still round.

Thank you all for your advice. I too am worried what went wrong. The car had not run for 12+ years, all checked out, several shake down runs, then a hard drive at 90 mph on a hot day. Oil pressure slowly went to zero and then engine gently stalled at speed. Oil pump checked out, sump was clean, brass foil in filter and elsewhere (big end bearing extruded around crank pin sides to create foil). Plan to magna flux and CLEAN all oil ways, check rod for round and fatigue, replace rod bolts, turn crank down 0.020 on rod pins & main bearings, new bearings everywhere, line bore, hone bores and rebalance lower end. Sound right?

Richard, you do know the engine is sleeved. You can replace the sleeve & bore to fit. Make sure you remove all the alen plugs from the crank & clean the oil galleys if you have it machined. Check the pressure relief valve in the oil filter housing.
Cheers Tom