Austin's 1977 Tintop Camper

[wwebner]

I was saving this for another topic but here you go. the short version
A number of years ago I was spending some time in the LA area. I spent a Saturday at Mark Stephens shop in Venice.
While I was there I watched as they had 4 T4 motors completely assembled,one in a vehicle,3 sitting aside.
Mark would take off and return about 20 minutes later. where upon they would swap the motor with one of the ones sitting aside. they di this with all 4 engines.

When I asked what they were doing, they said they were trying to find at what deck ht, the piston would kiss the head on a fully warmed up engine. The 4th engine was set at .020 and that is where the piston started to hit.

They determined that for high performance .0250,030 was a good deck ht with no problems. for street use such as our use in buses .030-.035 was optimum. This allows for slight variations in the crank center and small differences in rod length which can be a few thou. when combined.
A shorter deck ht also aids in the air/fuel mixture being compressed into the center of the combustion chamber as opposed to out at the side. Squish.

btw. Mark Stephens was doing type 4 performance when some of the current "gurus" were riding their tricycles.

[Kooper271]

I was saving this for another topic but here you go. the short version
A number of years ago I was spending some time in the LA area. I spent a Saturday at Mark Stephens shop in Venice.
While I was there I watched as they had 4 T4 motors completely assembled,one in a vehicle,3 sitting aside.
Mark would take off and return about 20 minutes later. where upon they would swap the motor with one of the ones sitting aside. they di this with all 4 engines.

When I asked what they were doing, they said they were trying to find at what deck ht, the piston would kiss the head on a fully warmed up engine. The 4th engine was set at .020 and that is where the piston started to hit.

They determined that for high performance .0250,030 was a good deck ht with no problems. for street use such as our use in buses .030-.035 was optimum. This allows for slight variations in the crank center and small differences in rod length which can be a few thou. when combined.
A shorter deck ht also aids in the air/fuel mixture being compressed into the center of the combustion chamber as opposed to out at the side. Squish.

btw. Mark Stephens was doing type 4 performance when some of the current "gurus" were riding their tricycles.

Awesome post, thank you for sharing that. .035" it is. Assuming I hit 70cc for my combustion chamber size that puts me at 7.5:1.

[wwebner]

I assume that your 70cc is your combined chamber volume plus your deck volume. I don't have the time to do the math right now,but your still a little ways away from build up

[Kooper271]

I assume that your 70cc is your combined chamber volume plus your deck volume. I don't have the time to do the math right now,but your still a little ways away for build up

Yeah I was just trying to get a feel for what changing deck height or chamber volume would do to the compression ratio.

Pistons come off tonight and anything else I feel like doing. Tomorrow I'll reorganize and regroup (garage is a mess) and this weekend split the case. Then the crankshaft goes to DPR (quoted me about $225 for my crank work) and the heads go to Delzani's.

I may call a couple local places before sending the crank out. Any recommendations?

[wwebner]

No. I don't know of any local shops that can do the crank work. assuming that you are having it counterweighted.
there are some that can do grinding, but I don't know who they are. All of the shops that I know send the crank out for grinding/polishing. DPR does great work. welding on counterweights without having to regrind the crank journals.
Allow at least 3 weeks to a month.

[Kooper271]

That's about what I figured. Thank you.

[wwebner]

I just went thru some old build notes and found stock1.8 and 2L heads were all measuring 50-54cc.

[Kooper271]

If that is the case for me I should be at a nice 7.7-7.9:1

[Kooper271]

Stupid question, but what does it mean to "lap the cylinder into the head?"

[Josh]

To put a valve grinding paste on the top of the jug and put it in the head and twist it back and forth to help it seal better. Obviously you would want to clean all traces of the compound off before assembly. I've never done it and haven't run into any problems, although I usually only put a few hundred miles on a bus before I flip it.